DIYstompboxes.com

Hello
Earlier I asked about the power filter, and I was given a magnificent response with detailed information that helped a lot.
I decided to ask more details about the protection against reverse polarity.
There are a variety of ways, but in stoppboxes the most popular are 2 ways (the diagrams below).
(https://1.bp.blogspot.com/-k4Hg3LuFsY4/WHLWe-6PhVI/AAAAAAAABGA/1XmTsTcStB4QN3vKtV5C7yeKDFUMGLr0wCLcB/s1600/power2.png)
(https://pp.vk.me/c636731/v636731754/3f5d2/yNbDn51SbHE.jpg)

These schemes are used both in DIY projects, and in boutique manufacturers and even from large manufacturers (BOSS / EHX / MXR).
The method using 1N4001 + resistor 10-100 ohm allows to protect the scheme circuit from reverse polarity. Its main advantage is that it does not lower the voltage and the effect gets as much as the power supply gives, but at the same time, judging by the feedback from the forums, it has a number of drawbacks:
1) In case of polarity error - the resistor burns out
2) There is a risk of burning the power source
3) If the diode dies before the resistor, then the probability of destroying full effect.

The scheme using 1N5817 is considered (again on forums) more advanced and reliable.
But has the following drawback - reduces the voltage by 0.45V.
When working with germanium fuzz and AIAB, it seemed to me that when the battery was sitting down (it was more than 8v, but I do not know how much exactly), problems were noticed
1) Oscillation of fuzz (Hello Fuzz Factory)
2) The amplifiers in the box sounded less convincing.
In the near future, I want to start studying the modulation, some circuits require a small power offset, for example 5V in Phase 90

So I'm not sure that the effects will work stably (although the site Madbean has now transferred its projects to 1N5817, although previously actively used 1N4001).

In general, I appeal to local gurus and experienced users with questions:
1) What method do you use?
2) Is there a way to improve reliability when working with 1N4001
3) Please tell us more about the principle of 1N5817 - its advantages and disadvantages, is it really reliable.
4) there may be good Schottky diodes that eat less than 0.45 volts (the power requirements I indicated below).

P.S.
1) The effects with which I work have negative earth, power from 9 to 18 volts, consume no more than 100mA
2) Yes, I heard about 2 circuits R G Keen using mosfet or 2 bipolar transistors. The circuit with bipolar transistors is very large and it is inconvenient when working with small pcb and a lot of details. MOSFET BS250P is very expensive, maybe it has the appropriate analogs, which cost not $ 3.

I was sure I already answered these same questions in your other thread, but here we go again.

Quote from: POTL on September 07, 2017, 06:21:29 PM1) What method do you use?

I use a modified version of RG's Cheap but Good circuit.

Quote from: POTL on September 07, 2017, 06:21:29 PM2) Is there a way to improve reliability when working with 1N4001

For low current applications like effects pedals, there is no way to improve the reliability of reverse-biased diode polarity protection. It provides adequate protection against momentary reverse polarity from a battery (with it's high source impedance relative to a power supply) accidentally connected backwards briefly, but that is all. Relying on a resistor to burn out is a bad idea, too slow, and will create a mess and damage anything else nearby. Fusing at low currents is tricky and unreliable, and low current fuses have high resistance, which given your insistence on absolute minimum voltage drop, will cause higher voltage drops than a series schottky.

Quote from: POTL on September 07, 2017, 06:21:29 PM3) Please tell us more about the principle of 1N5817 - its advantages and disadvantages, is it really reliable.

Series diode provides essentially perfect protection. It will only fail if the Vrrm (reverse voltage) is exceeded (20V for 1N5817). If you require higher reverse voltage protection, then the 1N5818 (30V) or 1N5819 (40V) are available, as are many other types. A 1N5817 has a forward voltage drop of around 0.18V at 10mA (some pedals will draw more, many will draw less), it'll only start dropping 0.45V around 1.5A! So don't know where you got that idea from.
So yes, it is really, really reliable. It's about as foolproof as you can get.

Quote from: POTL on September 07, 2017, 06:21:29 PM4) there may be good Schottky diodes that eat less than 0.45 volts (the power requirements I indicated below).

Yes, there are plenty of other schottky's out there, many with lower forward voltage at whatever current than the 1N581* series. They can all have different current/voltage curves, so you can't really make generalisations about which one will always have the lowest forward voltage, as that will be dependent on the current (and how much you want to spend).

Hopefully this answers your questions.

What he said.

New info. There is a variation of the MOSFET protection scheme that uses some active circuitry to make the forward drop of the MOSFET very low indeed. In fact, there are some  chips now that are intended solely to do this task (a) for a single series MOSFET, and (b) a long ago idea of mine that I got nowhere with, a full wave bridge of MOSFETs to make a pedal power supply be polarity-agnostic.

There are some gotchas on this front, but there's good news here for pedal power protection.

However, neither is a single diode. Sorry.

Quote from: Phoenix on September 07, 2017, 08:46:06 PM
I was sure I already answered these same questions in your other thread, but here we go again.

Quote from: POTL on September 07, 2017, 06:21:29 PM1) What method do you use?

I use a modified version of RG's Cheap but Good circuit.

Quote from: POTL on September 07, 2017, 06:21:29 PM2) Is there a way to improve reliability when working with 1N4001

For low current applications like effects pedals, there is no way to improve the reliability of reverse-biased diode polarity protection. It provides adequate protection against momentary reverse polarity from a battery (with it's high source impedance relative to a power supply) accidentally connected backwards briefly, but that is all. Relying on a resistor to burn out is a bad idea, too slow, and will create a mess and damage anything else nearby. Fusing at low currents is tricky and unreliable, and low current fuses have high resistance, which given your insistence on absolute minimum voltage drop, will cause higher voltage drops than a series schottky.

Quote from: POTL on September 07, 2017, 06:21:29 PM3) Please tell us more about the principle of 1N5817 - its advantages and disadvantages, is it really reliable.

Series diode provides essentially perfect protection. It will only fail if the Vrrm (reverse voltage) is exceeded (20V for 1N5817). If you require higher reverse voltage protection, then the 1N5818 (30V) or 1N5819 (40V) are available, as are many other types. A 1N5817 has a forward voltage drop of around 0.18V at 10mA (some pedals will draw more, many will draw less), it'll only start dropping 0.45V around 1.5A! So don't know where you got that idea from.
So yes, it is really, really reliable. It's about as foolproof as you can get.

Quote from: POTL on September 07, 2017, 06:21:29 PM4) there may be good Schottky diodes that eat less than 0.45 volts (the power requirements I indicated below).

Yes, there are plenty of other schottky's out there, many with lower forward voltage at whatever current than the 1N581* series. They can all have different current/voltage curves, so you can't really make generalisations about which one will always have the lowest forward voltage, as that will be dependent on the current (and how much you want to spend).

Hopefully this answers your questions.

Hi again
I was advised to create a separate topic so that it does not intertwine with the power filter.
In fact, in that topic everything was perfectly stipulated (regarding the power filters) and it can come in handy for a beginner in the future as an FAQ, because there is a lot of useful links =)
Regarding the information on the voltage drop of 0.18V - it's fine (much better than 0.45) I could not test today, but I'll try to do it tomorrow =)
Please tell me about the shortcomings and pros in more.
In the case of destruction of the diode, what is the probability that an ok passes through its stakes.
Is there a problem with the burnout of the power supply (as when using 1N4001).

I'm more interested in working with a power adapter than using a battery.
Thank you! =)

Hi POTL,

reverse polarity protection is basically a part of power supply filtering and what type of power supply filtering is best really depends on the pedal you need the power for.

The parallel diode method (because the diode is parallel to the power supply), as in your schematic with the 1N4001, is only really useful for very short term protection. The kind that happens when the poles of a battery quickly touch the wrong contacts. When using an external power supply, I would not do it like this.

The series diode method (low-drop diode such as 1N5817 in series with power supply) is essentially perfect except for the voltage drop you seem very worried about. But the fact of the matter is, that the 0.2-0.4V or so are rather small compared to the actual voltage difference between different supplies. When you buy a "9V" supply, that may actually put out 10V or 8.5V. And the voltage will change depending on how much current your circuit consumes and how linear the voltage output of the supply is. And batteries can drop to even lower voltages. So when you really need 9.00V at all times to feed your circuit, you need to do a whole lot more. It is possible but I cannot think of any instance where this would be remotely useful for a circuit that otherwise fits on a tiny PCB. Chances are, if your circuit is small, its probably a fuzz, booster, distortion or something of that nature. Those circuits are totally fine with quite a range of different input voltages. Sound will change a little bit but that can easily be compensated elsewhere in the circuit. In fact many fuzzes often sound better at lower voltages.

If you need 9.00V or some other precise voltage for some reason (some digital circuits may need that), I would use a series diode reverse polarity protection or better yet a bridge recifier, followed by a simple 5V voltage regulator, followed by a charge-pump, followed by noise filtering, followed by an adjustable precision voltage regulator set to 9.00V. But again, this is complicated and bulky and offers no benefit over the simple series Schottky diode for all but very, very few exotic effects.

Andy

Quote from: R.G. on September 07, 2017, 10:02:19 PM
a full wave bridge of MOSFETs to make a pedal power supply be polarity-agnostic.

More info, plzzzz ...  :icon_wink:

Oh, another thing that came to my mind: With a suitably sized precision rectifier you should be able to get exactly the input voltage but with always the correct polarity, no matter what polarity you feed it with. However, I have no idea what to watch out for in terms of design when they are being fed DC instead of AC. R.G. and PRR are the experts on that sort of thing, if I'm not mistaken. But this method too seems like a lot of unnecessary hassle.

Andy

@ antonis

This here explains that quite well:
https://en.wikipedia.org/wiki/Diode_bridge

But with that you have of course twice the voltage loss because you always have 2 series diodes. May or may not be a problem.

Quote from: Fancy Lime on September 08, 2017, 04:38:31 AM
Oh, another thing that came to my mind: With a suitably sized precision rectifier you should be able to get exactly the input voltage but with always the correct polarity, no matter what polarity you feed it with. However, I have no idea what to watch out for in terms of design when they are being fed DC instead of AC. R.G. and PRR are the experts on that sort of thing, if I'm not mistaken. But this method too seems like a lot of unnecessary hassle.

Andy

You'd also need a supply voltage for the precision rectifier, so how are we going to do polarity protection for that?
And it's voltage rails would need to be higher than the input voltage to be rectified, etc, etc. Sounds good at first suggestion, but quickly falls apart.

Quote from: Fancy Lime on September 08, 2017, 04:42:16 AM
@ antonis

This here explains that quite well:
https://en.wikipedia.org/wiki/Diode_bridge

But with that you have of course twice the voltage loss because you always have 2 series diodes. May or may not be a problem.

:icon_biggrin: :icon_biggrin: :icon_biggrin:
Thanks Andy but my concern is focused specifically on MosFets and more specifically on polarity-agnostic supply..  :icon_wink:

Quote from: antonis on September 08, 2017, 04:53:34 AM
:icon_biggrin: :icon_biggrin: :icon_biggrin:
Thanks Andy but my concern is focused specifically on MosFets and more specifically on polarity-agnostic supply..  :icon_wink:

Here you go Antonis, sorry about the ugly schematic!
(https://s26.postimg.org/xf04zf1ah/Mosbridge.png)

PMos...!!!  >:( :icon_evil:

Quote from: antonis on September 08, 2017, 06:41:12 AM
PMos...!!!  >:( :icon_evil:

And that's not the only downside unfortunately, you also can't power more than one device with the wall-wart/power adapter if this mosbridge is used, as there is a ground offset voltage. Even if all the devices powered all use the same mosbridge with the same mosfets and draw the same current, device tolerance means that the ground offset voltage will always be different between devices, and will cause serious ground-loop issues. Nice concept, in practice though, not really practical at all.

Quote from: Phoenix on September 08, 2017, 06:48:32 AM
Even if all the devices powered all use the same mosbridge with the same mosfets and draw the same current, device tolerance means that the ground offset voltage will always be different between devices, and will cause serious ground-loop issues.

Maybe not such a problem when deal with "foating" loads but we diverge from topic..  :icon_redface:

QuoteYou'd also need a supply voltage for the precision rectifier, so how are we going to do polarity protection for that?
And it's voltage rails would need to be higher than the input voltage to be rectified, etc, etc. Sounds good at first suggestion, but quickly falls apart.

Hi Greg,
right... I had not thought of that. But you're totally right, we'd need a second power supply, rendering the whole exercise ever more useless than I thought it was. So everybody please just forget what I said about the precision rectifier.

Andy

QuoteThanks Andy but my concern is focused specifically on MosFets and more specifically on polarity-agnostic supply.

Hi Antonis,
sorry, I thought you meant the general principle of polarity agnosticism. Anyway, as you can see in Greg's schematic it basically works the same with MOSFETS as it does with diodes, if you replace each diode with a MOSFET-resistor pair like you would use in a simple series diode protection to MOSFET conversion.

To get back to the original topic:
I still don't quite get what the drawbacks of series diode protection with a 1N5817 are. Loosing 0.2V or so? Where would that be relevant, all things considered? I have used PMOS protection in the past but gave up on that because I could never tell any audible difference to a plain old diode. The OP lists "Oscillation of fuzz (Hello Fuzz Factory)" as a problem. I never experienced anything like that, can anyone explain how a series diode in the power line cause that? To me that sounds like a capacitor related problem. Or one that could be fixed by a capacitor to ground in the right place.

Andy

Quote from: Fancy Lime on September 08, 2017, 09:38:42 AM
I still don't quite get what the drawbacks of series diode protection with a 1N5817 are. Loosing 0.2V or so?

That makes us - at least - two of a kind...  :icon_wink:

The issue of small ground offsets leading to noise and circulating DC currents is why I stopped developing the active bridge. What's different with the active drivers for the active bridge is that (a) they drive the MOSFETs HARD to give the lowest forward voltage possible, and (b) newer MOSFETs can achieve much lower forward resistances, so in combination the ground offsets ...can... be driven down into the millivolts. Will that be enough??? Who knows? Worse yet, there is the issue of "tolerance" on the tolerance of pedals for offsets. Today's pedal market, with literally tens of thousands of cottage pedal makers trying to sell on the pedal market ensures that some of them will be intolerant of even microscopic offsets in either voltage or resistance, and the protection mechanism or the power supply, not the IN-tolerant pedal will be blamed.

It's an insoluble problem, not because of the power supply technology, but because of the pedals.

As to whether losing a small amount of forward voltage is a problem, again the answer is a question: Which pedal are you talking about? Some will, some won't. Besides, losing a fraction of a volt is more of an issue when using batteries, where the voltage is certain to change over time, than when using active adapters, where the voltage will not change over time. As an "industry", where that's the term as used by anthopologists and archeologists, not techies, the pedal "industry" has moved to where batteries are a special purpose and slightly unusual answer, not what is the main-line answer to powering pedals. So losing a fraction of a volt is not as big an issue as it was when you forgot to change batteries and your 9V PP3s were down at 7.5V.

On the other hand, a PMOS transistor or a bipolar is good insurance for the issue of changing batteries; so is the single reverse-polarity diode.

What a reverse polarity diode is NOT good insurance for is someone with a giant pedalboard containing a L!ne & 9V>>AC<< pedal adapter connecting that adapter up to pedals with a reverse polarity diode. That scenario runs like: AC adapter overheats the diode, causes the diode to short; continuing high current burns the diode open; reverse polarity pulses now kill ICs; then they kill capacitor; then ....

The presence of AC-output adapters is the big issue. It doesn't get a lot of press, though. Only series protection - series diode, series transistor, etc. - can help you much with AC.  But then if you're not using batteries, you're not so worried.

This is one of those issues that isn't amenable to quick answers in a pedal forum. It needs some thought.

It would really be nice to get away from 9 volt batteries and positive shell connections for power.  If you are building a unit for yourself, a 12 VDC or 15 VDC wall wart supply makes everything better.  You don't need a Schottky diode because you can permit several volts of drop, so a 1N400X in series will do.  Even if you are stuck with batteries, many circuits can tolerate 18 volts as a power supply and others may only need a simple change of capacitor voltages to permit use at 18 volts.  I don't know any other industry that has stayed with a legacy power requirement for more than five decades.

If you are using a wall wart because the current consumption precludes batteries, maybe a relay with a diode in series with the winding would be a good protection switch - the diode in series with the winding to ground only permits current flow in one direction.  The switch only turns on with the correct polarity.  You could make it so the wrong polarity turns it off, but if the voltage is in the wrong direction but not enough to pull the relay in, you still get reverse voltage.

@amptramp

QuoteI don't know any other industry that has stayed with a legacy power requirement for more than five decades.

I don't know many other industries that are as traditionalist as (rock) music. We still build fuzzes that are trying to sound "exactly like Jimi at Woodstock", for cryin out loud. No, no, "live at Monterey was waaaay better, that was the ultimate, never to be surpassed guitar sound!". And lets face it, the real money to be made in stompboxes, guitars and amps is in selling millions of teenagers (some of them are in their 60s, mind you) stuff with which they supposedly sound like their heroes. Thank goodness we don't HAVE to abide by the traditionalist rules in the DIY world but can choose if we want to. Damn it, I'm ranting, aren't I. So, yes, I agree, there are good reasons to move away from 9V for some pedals. For others, it doesn't really make a difference, so we keep what we have. Inertia is a powerful force.

BTW: Is there something about power supply filtering and polarity protection methods in the Wiki of FAQs? I'd be willing to write something about the basics if someone would be willing to read the thing and correct mistakes and such. Don't want to confuse novices with poorly written half-truths.

Andy

Quote from: Fancy Lime on September 08, 2017, 03:21:29 PM
@amptramp

QuoteI don't know any other industry that has stayed with a legacy power requirement for more than five decades.

... there are good reasons to move away from 9V for some pedals. For others, it doesn't really make a difference, so we keep what we have. Inertia is a powerful force.

You'd be shoveling sand against the tide. This is one of those things you can't fix. It has to wear away, like eroding stone. Have you ever contemplated how different things would be if the early amplifier designers had used a single dual triode as a differential input, instead of a single ended amplifier input? Noise issues we struggle with would never have existed. Or that the "Japanese transistor radio" revolution in the early/mid 1960s had not happened, with the resultant rise in availability of the PP3/9V battery? The earliest pedal makers used AA or AAA cells. Then we got silicon, and the 9V battery was handy, and now the most coveted vintage effects demand 9V, so every older commercial pedal used 9V, and then the pedal hacker/solderer/cottage industry would not have been tied to 9V, and then...

The first entity selling something sets the standard. That's how Boss got us the center-negative polarity on adapter input plugs. But it is a truism that you simply can't rewrite history, nor change every one of the every user's minds. So the whole I'm-a-new-pedal-seller industry simply must use 9V because of the history, and there is no one with the clout to do things differently, excepting pedal makers who had to do it for other reasons - the digital people who needed vastly more power.

Sigh. Like I said, the unspoken "standard" is eroding over time, as the BUMS (Blind Urge to Mod Syndrome) crowd expands to using 12V and 18V to "improve" their 9V pedals. In that way, the standard is eroding. But you can't un-make thevintage fuzz face, nor can you un-convince people of what fuzz sounded good 50 years ago. You probably have to wait 20 years for the majority of those marginal players to age out of playing.

Quote
BTW: Is there something about power supply filtering and polarity protection methods in the Wiki of FAQs? I'd be willing to write something about the basics if someone would be willing to read the thing and correct mistakes and such. Don't want to confuse novices with poorly written half-truths.

I tried to do a lot of that with all of the "how tos" at Geofex, but the internet runs on new bodies, so the newbies go only to the newest pages, ignore the FAQs, and don't read the stickies. Teaching novices is hard. Getting their attention is even harder.

Hi
Thanks to everyone who responded, today I checked 1n5817 - this method on two mock-ups of three, my multimeter showed a drop of about 0.7V (what?), The layouts were powered by batteries.
The tone has really changed, but not globally, the low and high frequencies have slightly decreased.
In general, the difference is small, but my fuzzy model obviously does not like it, it starts to give oscillations when it drops below 8.6.
I decided to give up this protection.
The only way I came up with this is the detailed information next to the power socket.
In general, my observations - circuits using operational amplifiers do not pay attention to falling, when working with field effect transistors and germanium, the difference is more palpable.


Thanks for the advice.
In any case, I'm sure that the information voluminously submitted at work with one section of the scheme will be practical for other users.
This is much more convenient than ripping it to pieces from large sources.
This led me to think that it would be great if experienced users created a FAQ on different parts of the scheme, with brief but useful information.
For example, much can be pulled from my previous topic about power filters, there are links to calculators and a detailed explanation of the principle of operation of all components =)

Quote from: POTL on September 08, 2017, 04:01:11 PMtoday I checked 1n5817 - this method on two mock-ups of three, my multimeter showed a drop of about 0.7V (what?)

Did you purchase your 1N5817's from a reliable source like Digikey, Mouser, element14/Farnell/Newark/CPC, RS Components, Smallbear, etc. Or did you get them from eBay or Alibaba or something? 1N5817's don't drop that much voltage until about 1.5A, and that's only an instantaneous rating, not continuous. Sounds to me like you've got yourself some 1N400* that have been mis-labelled or you've been sold fakes.

Quote from: POTL on September 08, 2017, 04:01:11 PMit starts to give oscillations when it drops below 8.6.

I don't mean to insult, but if the design is intolerant of a 400mV drop, it is a bad design and needs revision. There's no reason such a small voltage drop should cause oscillation. You may need further decoupling, or to work on your layout.

@ R.G.
True, baby birds want to be fed directly to the mouth and would starve in front of a buffet. If that were not so, the we wouldn't need teachers in school, just books. Although that can be a bit frustrating, all is not in vain, I learned pretty much all I know about electronics from your and Mark's and Aron's and Craig Anderton's and Tim Escobedo's and Joe Davisson's and Jack Orman's articles, posts and schematics and I greatly appreciate the great work you guys have assembled there. But it would of course have been easier to just go to a forum and ask for directions from the senseis.

@ POTL
Greg is right, if your 1N5817 really drops 0.7V, then its not a 1N5817. And if your fuzz circuit starts to oscillate when supply voltage drops, there is something wrong with the fuzz circuit, not the supply protection. That should never cause a fuzz to oscillate. And it would also mean that an aging battery or simply using a different wall wart than you did when prototyping might cause oscillation. You need to get rid of this problem first, else the whole thing is practically unusable, imho. Have you accidentally built an oscillator into your fuzz, that is controlled via the input voltage and if voltage is high the oscillation is supersonic? Happens quite easily in a high gain circuit when there is positive feedback where it should not be (either by faulty design or short circuit on the board). If you could post the schematic, that may make the problem easier to diagnose.

Cheers,
Andy

It seems that I'm taking my words back =)
Today I decided to once again measured the voltage change when connecting 1N5817 and 1N4001
1N5817 ate about 0.1-0.12V
1N4001 ate about 0.4-0.45V
Either my multimeter deceived me, or the last time I measured it wrong.
Well, if my fuzz will work well, I definitely choose the side 1N5817
Once again, thank you all!

Quote from: Fancy Lime on September 09, 2017, 04:22:43 AM
@ R.G.
True, baby birds want to be fed directly to the mouth and would starve in front of a buffet. If that were not so, the we wouldn't need teachers in school, just books. Although that can be a bit frustrating, all is not in vain, I learned pretty much all I know about electronics from your and Mark's and Aron's and Craig Anderton's and Tim Escobedo's and Joe Davisson's and Jack Orman's articles, posts and schematics and I greatly appreciate the great work you guys have assembled there. But it would of course have been easier to just go to a forum and ask for directions from the senseis.

@ POTL
Greg is right, if your 1N5817 really drops 0.7V, then its not a 1N5817. And if your fuzz circuit starts to oscillate when supply voltage drops, there is something wrong with the fuzz circuit, not the supply protection. That should never cause a fuzz to oscillate. And it would also mean that an aging battery or simply using a different wall wart than you did when prototyping might cause oscillation. You need to get rid of this problem first, else the whole thing is practically unusable, imho. Have you accidentally built an oscillator into your fuzz, that is controlled via the input voltage and if voltage is high the oscillation is supersonic? Happens quite easily in a high gain circuit when there is positive feedback where it should not be (either by faulty design or short circuit on the board). If you could post the schematic, that may make the problem easier to diagnose.

Cheers,
Andy

I fully agree with your request to RG, I would add to this list Brian Wampler.
My fuzz is a germanium Tone Bender MKII with a switch to Fuzz Face / Tone Bender MKI
In Fuzz Face mode, he does not pay attention to the voltage drop, in TB MKII mode
he begins to create such sounds

I used this scheme
(http://fuzzcentral.ssguitar.com/mkII/mkIIschematic.gif)

The only change I made was the replacement of the resistor at the base of the first transistor, instead of the nominal value of 100K, I installed 22K.
This rating proved to be the best, it lowered the volume of the TM MKII to the FF level, while the level of the gain was the same, so it allowed to reduce noise (although it's worth trying to install a shunt capacitor in front of the base of the right transistor).
What characteristically I collected and other fuzz, the problem only occurs with TB MKII.
I used Russian transistors MP42B and GT402 (letters).
They sound great, easily accessible, cheap, in principle they can be obtained for free, because people who do not make music stompboxes just throw them away or give away for free. :D

I recently traded 3PDT for 10 GT402
And the other day I have to bring a box of different germanium transistors  8)

Using this thread, may I ask:
I've been using 1n5819 and 1N4007

I'm wasting my time?

1N400* series: as I read, the difference is in the amount of voltage inverse they can reach before breakdown (smoke like an old train..)
Normal Vf is ~0.7V

1N4001 = 50V
1N4004 = 400V
1N4007 = 1000V

About the 1N4148: Vf 1V

What about the 1N581* series?

20/30/40V for 1N5817/8/9.

I'm a bit late to the party but the 1N5817-scheme is not necessarily as perfect as assumed.

I already commented in another thread (here (http://www.diystompboxes.com/smfforum/index.php?topic=100033.msg1090763#msg1090763)) that I bought a whole bunch of an SMD variant of that diode (datasheet (https://www.vishay.com/docs/85682/sd103aws.pdf)) because I thought that would be perfect – super small, low voltage drop, cheap – but then a customer just tried any PSU he had lying around and hooked an (suspected) AC source to the pedal. The diode didn't burn through but opened up and took a precious LT1054 with it. Now I made myself some pcbs for RGs cheap and reliable reverse protection. But I must say: one diode was easier!

How would AC harm the reverse polarity protection? How can a diode open to reverse polarity without burning through?

I had a (maybe) similar case, when a customer kept returning a pedal with burned out op-amps (bloated and scorched) despite power protection. He insists he only ever used a correctly polarized 9V PSU. Yet I could never replicate the problem because I never managed to burn the thing with any of my PSUs. I suspected a faulty PSU back then that put out a lot more than 9V. That is the only reason I could think of because the pedal had reverse polarity but no over-voltage protection.

Andy

The short answer is:
- series protection use Schottky for lower drop.
- parallel protection use silicon rectifiers like 1N4004 - as in most cases you are wasting your money using a Schottky.

Quote from: lars-musik on September 15, 2017, 05:24:15 AM
I'm a bit late to the party but the 1N5817-scheme is not necessarily as perfect as assumed.

I already commented in another thread (here (http://www.diystompboxes.com/smfforum/index.php?topic=100033.msg1090763#msg1090763)) that I bought a whole bunch of an SMD variant of that diode (datasheet (https://www.vishay.com/docs/85682/sd103aws.pdf)) because I thought that would be perfect – super small, low voltage drop, cheap – but then a customer just tried any PSU he had lying around and hooked an (suspected) AC source to the pedal. The diode didn't burn through but opened up and took a precious LT1054 with it. Now I made myself some pcbs for RGs cheap and reliable reverse protection. But I must say: one diode was easier!

Quote from: Fancy Lime on September 16, 2017, 09:01:14 AM
How would AC harm the reverse polarity protection? How can a diode open to reverse polarity without burning through?

The power supply was an AC wall-wart, so was small, and therefore had poor regulation. Remember, a 9VAC transformer actually puts out ~12.7V peak, and higher off-load. An LT1054 has a max voltage of 15VDC, so it would only take 18% regulation to exceed its max voltage and burn it out. Once it had gone short circuit, it would destroy the schottky.
Typical AC wall-warts have regulation as poor as 30%, so this is not at all surprising.

If my logic is correct, then RG's cheap but good circuit wouldn't have protected the device in this instance, because it does not have over-voltage protection, however, with the addition of a couple more parts, RG's circuit can be made to also provide very robust over-voltage protection too.

Quote from: Rob Strand on September 16, 2017, 09:44:13 AM
The short answer is:
- series protection use Schottky for lower drop.
- parallel protection use silicon rectifiers like 1N4004 - as in most cases you are wasting your money using a Schottky.

Where do you buy your diodes? Where I usually buy, a 1N5817 costs a whopping 0.06€ more than a 1N4001. I would have to buy over 100 diodes to save enough money to buy one beer at a bar by going with the cheaper diode. Granted, even in series mode using a 1N400x is not going to have an audible effect in most cases. But when voltage drop is a concern and you want to avoid more expensive and/or complicated protection measures, I think the advantages of series protection by far outweigh the minuscule savings of going parallel with a 1N400x.


@Phoenix
Ah, that explains it. in the end, the dilemma with protection is how much to trust the user. Are we nice and try to make it absolutely idiot proof or are we cynical and say "if you cannot or will not follow clear instructions about which power supply to use, you do not deserve to play this thing anyway". Unfortunately, in my experience at least, many musicians are complete technical (or electrical) dyslexics who struggle with the concept that electricity comes in different forms and strengths. I once spent quite a while explaining to a guitar player that "having different looking connectors" is not the only difference between a wall power outlet and a 9V Boss-connector.   

Andy

Quote from: Fancy Lime on September 16, 2017, 09:01:14 AM
How would AC harm the reverse polarity protection? How can a diode open to reverse polarity without burning through?

When the "don't use AC" issue came to light, it came up with customers from my day job calling in to tell us that our extensively-protected and tested DC power supply for pedals was killing their pedals. I spent quite a lot of time doing lab work to find out what was happening. I'm sure other people might have found this out first, but to the best of my knowledge I brought this issue to light in the pedal community. It works like this.

AC-only supplies are simple transformers, not active power supplies with current limiters. An actively regulated supply will limit its output current to some value simply to protect itself, and its load. Transformers do not.

So a transformer feeding a circuit with a reverse-polarity diode feeds the circuit a half-sine wave in the forward direction, but is "shorted" by the reverse protection diode in the reverse direction. The only limit on how much current flows in the diode is the diode's forward resistance, which is deliberately as small as it can reasonably be made, the resistance of the lead wires, and the resistances of the transformer windings. These are all, in fact, as small as they can reasonably be made. So the reverse current in the diode is not  just the limited current that a reversed regulated DC supply will produce at limiting, but "large".

That's OK for a while, as the pulsed current rating of a silicon diode is quite a bit larger than its DC average current rating. But it does cause heating, and the diode heats up. The diode's thermal time constant is short, as it's small and low mass, so in a short time, the diode heats quite a bit. A couple of things can happen. One is that the diode can de-solder itself. I've seen this happen in a couple of experiments. Another possibility is that the very hot diode can exceed the thermal rating of the silicon chip inside the diode, and the junction will get over the 150-200C that the junction can stand, and you'll get large enough currents in the chip that it will punch through.

When that happens, the diode conducts as a relative short in both directions. This doubles the currents going through it, as it now has large currents in both directions. So the diode gets even hotter.

What can happen then is heavily dependent on tiny differences in the setup - a kind of "Butterfly Effect" for thermal disaster. The diode can simply sit there heating, and char a spot on the PCB under it. If the transformer feeding it has enough current capability into a short, it can even burn through the PCB. Mostly the transformers are small and can't quite do this. It can unsolder itself in the second phase of thermal disaster. Or it can burn through the bonding wires or open the wire-to-chip solder connections on the chip itself. In any case, it can burn open.

While the diode is shorted, it has been protecting the circuit from the reverse polarity half-cycles. When it opens, it is no longer part of the circuit and the AC starts killing chips and other polarized things in the rest of the circuit. How far this goes depends on how long they heat. Opamps die pretty quickly. Other things take longer.

I did experiments with out power supplies and diodes, leaving them reverse collected for long periods of time. The diodes only got a bit warm, as the protection clamped the currents to the supply max, the supply shut down and waited to retry. I could never damage a diode with our supplies. I connected diodes to 9Vac 1A wall warts, and the would smoke in minutes.

The real crux of the problem is that the plug on the 9Vac adapters as used by L!&# 6 is a 2.5mm center pin, 5.5mm outer barrel, and this can be forced into most DC 2.1mm/5.5mm sockets. Grab the wrong plug and plug it into your daisy chain, and you start killing pedals.

Hi R.G.

thanks for the detailed explanation. Just to be clear: does that apply to both single diode protection schemes, series and parallel, or just parallel? For the parallel case I see how the scenario you describe would play out. But for series protection there should be no current through the diode during the reverse polarity half-cycle of the AC, correct? And during the forward polarity half-cycle the current is limited by the effective load resistance of the circuit, isn't it?

Thanks,
Andy

Quote from: Fancy Lime on September 16, 2017, 10:44:35 AM
thanks for the detailed explanation. Just to be clear: does that apply to both single diode protection schemes, series and parallel, or just parallel?

Yes, just the reverse-parallel situation. For series diodes, the polarity is always in the correct direction, even though with a 9Vac pedal, the peak voltage is larger than the "9v", about 12.7V nominal.

The only objection to a series diode is the voltage drop. Schottky diodes are good for having a lower voltage drop, but they have a reverse breakover level of as little as 20V. Not a big deal, but still there.

The point of more complicated series protection schemes is that they can give the same series protection without the forward drop. The MOSFET series scheme can be as low a voltage drop as you want to pay for the MOSFET, and the "Cheap But Good" bipolar scheme got down in the tens of millivolts, although it also has its own reverse voltage breakdown issues.

I really liked the idea of an active MOSFET bridge, because polarity is no longer a concern, full stop. All variants just work, given that you can provide too much voltage with an AC power supply fed to it and full wave rectified to the peak of the AC. There are still those issues of millivolts of ground offset, but hey, nothing is perfect.

Quote from: Rob Strand on September 16, 2017, 09:44:13 AM
The short answer is:
- series protection use Schottky for lower drop.
- parallel protection use silicon rectifiers like 1N4004 - as in most cases you are wasting your money using a Schottky.

Often I hear that the Schottky is more expensive, but I see the price tag at 1N4001-0,05 $ / 1N5817-0,07 $, when buying several hundred the price will be equal to half.
Funny difference in price.

Once we're at the "complicated but awesome" circuit protection topic: I was wondering why not use two relays that are controlled by transistors in such a way that with no voltage the circuit is cut off from the power supply (+ and - leads) and then two relays switch the appropriate power input lead to the right rail of the circuit, depending on polarity of the power supply. Expensive, bulky, complicated and (unlike diode or mosfet bridges) too slow to deal with AC, but on the other hand: DC power can be connected either way round and there is (nominally) no resistance in the ground wire. Not that this is really practical or necessary but it should be possible. Yet I have never seen this used and normally it seems that if it's complicated and could be sold as "more advanced" and it's at all possible, someone is using it, no matter how unnecessary.

Cheers,
Andy

I think there is a hidden catch with the series diode scheme. You may have gone to the trouble and expensive of getting a really well regulated, smoothed, low noise DC supply. Does the series diode in the pedal +9v affect the supply at the pedal in any way, apart from the diode voltage drop?

The supply will almost certainly be using a reasonable amount of capacitance on it's outputs. When the pedal circuit is sucking DC current, the series protection diode is forward biased and as much current as it needs will pass. But, what about AC signal current? We have put a rectifier in there.

Stop and consider all the ancient & not so ancient pedal circuits that have zero power rail capacitance built in. They worked fine with a battery, because that comes with a lot of capacitance built in for free. They work ok too if a DC supply with sufficient capacitance isn't too far away and may also benefit from other pedals on the same DC that do have supply capacitors. However, the existence of the series protection diode means that signal currents (though they may be tiny) are blocked in one direction by the diode. This can easily result in audible distortion. That distortion can be really horrible where signal currents are not small, such as 9v practice amps.

I think series protected pedals must have relatively large local supply capacitors to handle all the signal current needs. 100uF is good without taking too much space and use a 25v rating so it won't mind an 18V supply accidentally or deliberately employed.
Chip amps need a lot more C. At least 1000uF will keep them happy.

Hi Jim,

you mean an additional cap between the rails before the diode? Or just the "normal" one after the diode (and series R), which imho should always be there, no matter what the protection scheme.

Andy

Definitely after the diode - the diode would block the capacitor if it were before the diode.

QuoteWhere do you buy your diodes?

QuoteOften I hear that the Schottky is more expensive,

The price certainly depends on your sources.
Some small vendors want near $1.00 each and people's local store in some countries might not even keep Schottky's.

The small-time hobbyist and one-time builders have different limitations to people doing production.

My post stands from a technical perspective but there are of course many other factors.  Like a design might *have to* use 1N4004s in one location so in order to minimize part you might choose an 1N4004 in another location.  When you use surface mount parts you might not want to buy 4k reels of two parts.  Reducing the number of parts can help reduce supply problems as well.

I only wanted to give a short answer!

> The only limit on how much current flows in the diode is the diode's forward resistance, which is deliberately as small as it can reasonably be made, the resistance of the lead wires, and the resistances of the transformer windings. These are all, in fact, as small as they can reasonably be made.

For clarity of theory, or for folks doing smoke-tests at home......

"as small as ...reasonab[le]" can be read "as small as you PAID for". You pay for V times A, and get just low enough resistance to get what you paid for.

Transformers in general can output 10 times their rated current, into a short, for a short time.(*) For the "1 Amp" tranny mentioned, 10 Amps.

Transformers are massive, take a long time to burn up, minutes. OTOH, as R.G. says, diodes heat quickly.

So, as R.G. says, a "1A" AC wall wart can usually burn-up a "1A" diode. And (as said) melted diodes often go "short" both ways, at least for a while. Sometimes they eventually burn open, sometimes they don't (depending maybe on just how much current flows).

(*) "10 times" is a starting point for thinking/guessing. In practice, small transformers are cheap, in every way, including excess winding resistance. If you smoke a few, you may find that ~1A warts may "only" deliver 5X rated current into a short. OTOH, big transformers are more about efficiency. The 100 Amp street transformer feeding my house can deliver 50X rated current. Partly for low loss at nominal load, and also so a short will burn-up a drop-wire quickly and save the transformer.

QuoteTransformers in general can output 10 times their rated current for a short time.(*) For the "1 Amp" tranny mentioned, 10 Amps.

Transformers are massive, take a long time to burn up, minutes. OTOH, as R.G. says, diodes heat quickly.

So, as R.G. says, a "1A" AC wall wart can usually burn-up a "1A" diode. And (as said) melted diodes often go "short" both ways, at least for a while. Sometimes they eventually burn open, sometimes they don't (depending maybe on just how much current flows).

Very true.

I have a very old plug pack rated at 300mA, with known poor regulation and hence lowish short circuit current. The short circuit current is 1A.   Once the output got shorted for many hours.  It got freakin hot..  However because it was from the bad old days it didn't have the (one shot, non-replaceable) thermal fuse you see in modern units.  It survived.

The short circuit current/rated current ratio goes up disproportionally as you increase the rating.

I have several plug-in doorbell transformers rated from 10 to 14 volts.  They are distinguished by the fact that they have enough series leakage inductance that they can operate with a shorted output because the current does not rise to a value they cannot tolerate.

These could be a good choice for a pedal power supply since you could have the supply (either AC or DC) plugged into a pedal with the centre pin grounded then have the barrel of the output grounded accidentally, maybe for some time.  It would also be good for parallel protection since the input current is strictly limited and could be set to a value a diode could carry permanently.  Some of them plug directly into a wall outlet and have screw terminals on the back for the output so they are like wall warts from before the days of wall warts.

Quote from: Fancy Lime on September 08, 2017, 03:33:58 AM
The series diode method (low-drop diode such as 1N5817 in series with power supply) is essentially perfect except for the voltage drop you seem very worried about. But the fact of the matter is, that the 0.2-0.4V or so are rather small compared to the actual voltage difference between different supplies.

+1
I used to worry about the series diode drop when I was a beginner. Since then I've matured, series Schottky is fine and gives best value for money IMO. Worrying about <0.5V drop on the rail is misdirected attention; it's bugger all and you can always claw back more than that by swapping to rail-to-rail opamps. Except nobody bothers with that because <0.5V is bugger all!

QuoteWorrying about <0.5V drop

It does waste battery capacity. (Not that I use batteries much.)
With the cost of 9V batteries these days the % loss adds up quite quickly.
The more elaborate solutions give you payback quite quickly!

Quote from: Rob Strand on September 20, 2017, 05:24:35 PM
The more elaborate solutions give you payback quite quickly!

Does it, though? For a low-draw fuzz or something similar, batteries can have years of life in them and I for one would always use cheap zinc-carbon batteries for that. For a Flanger or whatever, that draws a lot of current, battery operation makes no sens anyway, economically, ecologically or just plain practically.

Andy

"Elaborate solutions" - and schottkys - can both give you a slight un-ease. When you think about it, and simplify, you have to deal with two major nuissances: the reverse leakage thing, and the failure mode. Both can (and most probably will) damage the circuit they are supposed to protect, in case "something goes wrong" and exploit precisely those two weaknesses.

When you think about it some more, and you seek a "stupidly simple & reliable" - and possibly affordable solution, you really can't ignore the exactly "wrong" thing to do: two (or more) ordinary Si rectifiers in parallel (!!) It's cheap, and lower leakage compared to schottkys, withstands significantly more reverse voltage etc. etc.

If you proportion the circuit current consumption to fall within the lower forward drop knee of the diode, you can of course minimize the said drop.

In short: SM4004's and SM5404's are a cost effective and sturdy solution that wastes a little portion of your PCB real estate.

You can beat around the bush as much as you want, but that's the way it is.

Hi bool,

I'm afraid I don't quite follow.

Reverse breakdown voltage (which I assume you mean with "failure mode"?) is 20V for a 1N5817 or 40V for a 1N5819. So enough for someone plugging in a 9-18V universal PSU with the polarity switch in the wrong position. And if someone insists on hooking their stompbox up directly to 220V AC power, there is not much hope of reliable protection anyway. But that will hardly happen by accident. Thats why vastly different voltages and power ratings use different connectors.

I could not find reverse leakage data quickly but I would be surprised if enough voltage came through to destroy even a sensitive circuit. Definitely not for anything discrete transistor based and almost certainly not for most common modern op-amps. If it does, there is something else wrong with the circuit.

If you have two diodes in parallel, wouldn't just one open? The voltage drop across one diode is exactly what the other diode of the same type would nominally need to open. So unless they are exactly identical, only the one with the slightly lower drop will open, leaving you with the same 0.7V as before. Things change when the forward drop increases due to high power draw, then you can open both. But then again, if your stompbox eats 3 amperes, you have a whole other sort of problems.

I see your solution work and be relevant for a space heater, kitchen stove, dryer or other high power appliances, but for a 9V stompbox, I don't see how this would be useful. So, to beat around the bush some more: no, I really don't think that thats the way it is.

Respectfully,
Andy

Think whatever you like... that's your constitutional right :)

What it is that makes the described configuration work is the fact that diode junction resistance somewhat varies with the passing current; and if diodes are over-specified in that regard just enough (i.e. for a couple milliAmps or couple tens of milliAmps), said diodes will act somewhat as paralleled resistors; sharing the passing currents.

By reading the datasheets, it won't be too difficult to locate (and extrapolate) the combined V drop at a specified passing I ...

And the combined V drop will be a little lower for paralleled diodes than for a single diode.

Quote from: bool on September 21, 2017, 09:07:36 AM
Think whatever you like... that's your constitutional right :)

What it is that makes the described configuration work is the fact that diode junction resistance somewhat varies with the passing current; and if diodes are over-specified in that regard just enough (i.e. for a couple milliAmps or couple tens of milliAmps), said diodes will act somewhat as paralleled resistors; sharing the passing currents.

By reading the datasheets, it won't be too difficult to locate (and extrapolate) the combined V drop at a specified passing I ...

And the combined V drop will be a little lower for paralleled diodes than for a single diode.

You can't simply parallel diodes like that though - that's NOT how they work. Diodes are like any other semiconducter material, there are always slight variances, regardless of if the diodes have come off the same reel, been made at the same factory, made from the same bool of silicon. There will be slight variations in their doping, and therefore their forward voltage, it's just the nature of the beast. This is why high power diodes are made, and we don't just use lots of little diodes in parallel.

Now, in high power stuff, doides often ARE used in parallel, however, they MUST have ballast resistors in series with them (so the diodes themselves aren't actually in parallel, it's a series diode-resistor pair in parallel with others), because otherwise, whichever diode has the lowest forward drop will conduct ALL of the current, while the others in parallel sit there and do basically nothing, until the first one burns up, and then the one with the next lowest forward voltage steps up to the plate to sacrifice itself in a vain attempt to save the others. The difference in forward voltage only has to be microvolts, it doesn't make a difference.
However, if you have some ballast resistors in series with each diode, they will help to balance the current between the diodes, because if any one diode is conducting more current than another, the voltage drop across the resistor will increase, leading to some self-balancing.

Andy's quite correct, the forward voltage will always be the same, the only time that you use parallel diodes (with ballast resistors) is when you can't get one with the current ratings you require for a price you're willing to pay, or in a form-factor that's suitable for your application. Yes, forward voltage increases with increased current, but even for high-current digital pedals that's frankly a non-issue, any of your typical rectifier diodes that can be had for $0.005 each in 100's of quantity are nowhere near their knee at the currents we demand of them. Seems you have a fundamental misunderstanding of how diodes work.

That's correct whent diodes run at their rated pass currents.
Their junction parasitic R will increase when ran at significantly smaller currents compared to their rated current; and consequently this internal parasitic R will accomplish what otherwise externall added ballast resistors would.

(JK: If it wasn't so; diode bridge compressors wouldn't exist).

[pardon]

Quote from: Phoenix on September 21, 2017, 10:25:07 AM
....  made from the same bool of silicon. There will be .......

ohhh, well played.
[/pardon]

Well played indeed. But it is Mr. Phoenix who is coming along as a bit too smart for what he is preaching. (I would just quietly move along as if I didn't notice it if you didn't push it like that).

What I described above is a mechanism that is a basis of operation of some very expensive (with a reason) studio compressors - diode bridge compressors. So guys, learn more before you serve generic text-book answers.

Exact same parasitic characteristics of diodes can be used to drop the forward drop a little (usually a couple tens of millivolts) cheaply. The answer to what I described is staring at you right from the datasheet.

F.e, download here
www.vishay.com/docs/88503/1n4001.pdf
Look at Fig.4; and extrapolate. Take f.e. a passing current of 20mA.

The current-sharing balance between several un-padded diodes (as will be the case with crude paralleling) won't be ideal, but just from the graph, it is obvious that the voltage drop is going to be lower than compared to a single diode. A soon as you move current-wise into the lower portion of the fw. characteristics knee, what I described is just how it works.

It's a no-brainer really.

@bool

I and I'm sure many others before me have had your idea as well and wondered: Why does no-one use this obvious and perfect solution? General rule of thumb that I and I'm sure many others before me have learned along the way: If it's obvious and perfect and nobody has ever thought of it, it's almost certainly not going to work. Not to discourage anyone of course... but if someone tries to tell me that they invented a perpetuum mobile, cold fusion, the levitation machine or that a Nigerian Prince wants to give me half his inheritance for a small service fee, I have to make a conscious effort keeping to take them seriously.

I don't see what Fig.4 has to do with this. It shows the instantaneous forward current vs instantaneous forward voltage. What you are describing has to do with resistance vs forward current (like in a diode bridge compressor).

Quote
What I described above is a mechanism that is a basis of operation of some very expensive (with a reason) studio compressors - diode bridge compressors. So guys, learn more before you serve generic text-book answers.

Well, partly but not quite. The poblem is, that you are missing a different, much more important factor. Let me try to explain:

The solution you propose relies on the parasitic resistance increasing with increasing current. For this to balance the currents between two diodes, this relationship would have to be stronger than the dependence of the breakdown on the voltage. And that is simply not the case in anything that can reasonably be defined as a diode. It is not like the effect you describe does not exist, its just that there is another much stronger effect canceling it out. What you describe assumes that a diode behaves mostly like a resistor. But it doesn't. It behaves a little bit like a current dependent (or voltage dependent because those two are coupled as well) resistor but it also behave a lot like a diode. In a diode bridge compressor that does not matter because there are no identical parallel paths and we can use the little bit of resistor behavior without the diode behavior messing things up. I won't say hat there are no diodes with which your technique would work. But those would be diodes that are terrible at being diodes. With a modern Si power diode, I don't see this happening. Just try and measure it. If you parallel several diodes you will get a drop that is slightly below the drop of a single one because one diode is open but still has some resistance and the other is closed but lets a tiny bit of voltage through due to the small parallel resistance it sees.

Hope that was comprehensible,
Andy

Let me put it that way: have you ever seen a circuit that uses a BAV70/65 or a BAS40-05/06 that has both halves in parallel? It happens, I'm afraid.

Otoh, you have already given yourself half of the answer when pondering on the Fig.4. Just think a little deeper. It's simple.

Disclaimer: just don't ever do this to "up" the diode current ratings on the cheap.

Hi. I don't want to clutter up this forum with regular silly topics, on this I will revive the old one.
I was looking for a replacement for the 1N5817 in a compact smd package.
And found this diodes MBR130LSFT1 & MBR120VLSFT1
I looked at the specifications and it seems to me that it is even better, but I am not an engineer and could have missed something.
It will be used in conjunction with icl7660s / max1044 to double the voltage.
what do you think?
https://www.onsemi.com/pub/Collateral/MBR120VLSFT1-D.PDF
https://www.onsemi.com/pub/Collateral/MBR130LSFT1-D.PDF
and classic
https://www.onsemi.com/pub/Collateral/1N5817-D.PDF

nobody?

I have some SMD 5817 diodes that I use, give me a second and I'll find the part number for you. They absolutely exist.

Try out the SM5817 or B5817. Same thing as 1N5817, SMD package.

https://www.mouser.com/ProductDetail/Micro-Commercial-Components-MCC/SM5817PL-TP?qs=sGAEpiMZZMtQ8nqTKtFS%2FEo19YTfnJP1ysRBdx90Swg%3D

Quote from: vigilante397 on May 01, 2019, 07:25:58 PM
I have some SMD 5817 diodes that I use, give me a second and I'll find the part number for you. They absolutely exist.

Try out the SM5817 or B5817. Same thing as 1N5817, SMD package.

https://www.mouser.com/ProductDetail/Micro-Commercial-Components-MCC/SM5817PL-TP?qs=sGAEpiMZZMtQ8nqTKtFS%2FEo19YTfnJP1ysRBdx90Swg%3D

Hi, thanks, I know that 1N5817 exists in the form of smd.
I just wanted to use a more compact body, not that it is an urgent need, but sometimes it can be useful  :)
I looked for possible replacements and found 2 models from the same series, they look good, but I'm afraid I can miss something in their specifications.

Quote from: POTL on May 01, 2019, 07:51:05 PM
Hi, thanks, I know that 1N5817 exists in the form of smd.
I just wanted to use a more compact body, not that it is an urgent need, but sometimes it can be useful  :)
I looked for possible replacements and found 2 models from the same series, they look good, but I'm afraid I can miss something in their specifications.

Ah, gotcha. Just took a quick look at the datasheets, either of those diodes should work fine as a replacement for 1N5817.

Quote from: vigilante397 on May 02, 2019, 12:00:10 PM

Quote from: POTL on May 01, 2019, 07:51:05 PM
Hi, thanks, I know that 1N5817 exists in the form of smd.
I just wanted to use a more compact body, not that it is an urgent need, but sometimes it can be useful  :)
I looked for possible replacements and found 2 models from the same series, they look good, but I'm afraid I can miss something in their specifications.

Ah, gotcha. Just took a quick look at the datasheets, either of those diodes should work fine as a replacement for 1N5817.

thank
As for the datasheet, I was afraid that there are pitfalls in the spirit of heat dissipation and other things. thanks again)
P.S. 1N5817 is sold in my country only as a DO-213AB, it is still big.

Quote from: POTL on May 02, 2019, 12:05:25 PM
P.S. 1N5817 is sold in my country only as a DO-213AB, it is still big.

Do you even need a 1A diode? A BAT54 is rated for 200mA... And you can use a BAT54A and connect the two devices in parallel for lower drop.

No, just 5817 proved to be a good solution, MBR130LSFT1 & MBR120VLSFT1
look no worse, and the voltage drop is even smaller.
I was just looking for the closest-in-band analogue in the smd package and the minimum voltage drop, that's all.

I don't suppose anyone ever took a DMM to the "parallel diodes" hypothesis?

Andy

> I don't suppose anyone ever took a DMM to the "parallel diodes" hypothesis?

Not for this application; but general theory suggests ~20mV less drop. (Which is probably not worth a second part, but Merlin cites a dual-diode so it is just one added connection.)

I think Merlin's suggestion was to increase the current handling of the device by paralleling the two in the package. This would bring the total current limit to 400mA. The slight Vf drop is just a beneficial side effect.

Quote from: Phoenix on September 08, 2017, 06:48:32 AM
And that's not the only downside unfortunately, you also can't power more than one device with the wall-wart/power adapter if this mosbridge is used, as there is a ground offset voltage. Even if all the devices powered all use the same mosbridge with the same mosfets and draw the same current, device tolerance means that the ground offset voltage will always be different between devices, and will cause serious ground-loop issues. Nice concept, in practice though, not really practical at all.

I decided to re-read this topic.
Did I understand correctly that mosfet polarity protection devices are unsuitable for pedalboard work?
If I want to power different effects from one power supply and there will be at least one pedal with a stack of protection among them, can there be problems?
What is the point?

I use TO92 P MOSFET reverse polarity all the time. Works great for me.

It's correct if you're using N-channel MOSFETs and low-side switching, as there is no such thing as an RDS-on of 0, so there will be a ground offset between devices, potentially making things wonky. Granted if you used a P-channel MOSFET and did high-side switching it would be fine.

Personally I like using schottkey bridge rectifiers for polarity protection. Low input voltage drop, and it not only won't be damaged by the wrong polarity, there is no wrong polarity so it can work with anything 8)

Quote from: vigilante397 on July 06, 2020, 06:47:38 PM
It's correct if you're using N-channel MOSFETs and low-side switching, as there is no such thing as an RDS-on of 0, so there will be a ground offset between devices, potentially making things wonky. Granted if you used a P-channel MOSFET and did high-side switching it would be fine.

Personally I like using schottkey bridge rectifiers for polarity protection. Low input voltage drop, and it not only won't be damaged by the wrong polarity, there is no wrong polarity so it can work with anything 8)

Problem only with N-channel mosfets?
I thought everyone uses only p-channel mosfets.
Ok p-channel = no ploblems
thank

https://youtu.be/IrB-FPcv1Dc (https://youtu.be/IrB-FPcv1Dc)
Good reference video. Note the end about the RDS on.

Yes, I am aware of RDS.
It is good that this protection does not create problems for use with other pedals.
In my store now available bsp250 and irfr9024 at a price of a little less than $ 0.5, I'll definitely try.

Hey hey new member....

Hope it´s ok to do this, posting a question in a half-dead thread. 

I somehow seems to have given my RAT a dose of juice with the wrong polarity.  The little resistor closest to 9v in on the card has blown, a load of gunk had shot out around it and it´s pretty much charcoal now !!...I first thought it was a diode but thats just next to and it is ok...tested with multimeter. 

I read somewhere, electrosmash maybe, that it will be fine with any resistor up to 100 0hm .. can anyone confirm this ??

Everything else seems to be fine but im no expert...anything i should check out in perticular.

Sorry if this post is not ok...

// M Wenander

Hi & Welcome.. :icon_wink:

That resistor forms a Low Pass Filter with 100μF capacitor and also serves as a "fuse" (like in your case)..
Original is (was) 47R but any value up to 100R should be fine..
Actually, the bigger resistor the better LP filtering, as long as you can afford the extra voltage drop..
(which drop is resistor value times circuit total current draw..)

Quote from: antonis on December 06, 2022, 04:04:27 PM
Hi & Welcome.. :icon_wink:

That resistor forms a Low Pass Filter with 100μF capacitor and also serves as a "fuse" (like in your case)..
Original is (was) 47R but any value up to 100R should be fine..
Actually, the bigger resistor the better LP filtering, as long as you can afford the extra voltage drop..
(which drop is resistor value times circuit total current draw..)

Thank you.

47R ???  whats the R ??? 

i found a 102 ohm resistor .. the closest match i have found. 

Are there any risks involved with trying to use it ??  or is the only risk that nothing happends ?? 

I´m thinking with a battery it should be safe ??  or doesnt it matter if i use a pedalpower thingy ?? 

(and off-topic .,.. how do know that someone has answered ??  i had to go search for the thread and manually look here to find this?!?)

47R is just a common way of writing 47 Ohms.  R is also sometimes used as the decimal point so 4R7 means 4.7 Ohms.

Antonis suggested a 100 Ohm resistor but 102 Ohms is fine as a substitute for your purposes.

Quote from: Wenander on December 13, 2022, 07:28:59 AM
......

(and off-topic .,.. how do know that someone has answered ??  i had to go search for the thread and manually look here to find this?!?)

also welcome. at the top of each page, under your username, is two links - one of which is:

Show new replies to your posts.

clik that and it shows all the topics you have posted in that have had any activity since.

and - at the top and bottom of each thread page is a bar of buttons, thusly [but horizontal]

REPLY
ADD POLL
NOTIFY
MARK UNREAD
SEND THIS TOPIC
PRINT

I don't use it, but I imagine the "notify" button, when clicked will, well, notify you of a reply or something.