So why don't we use NE555 for voltage doubling and negative voltages?

[frequencycentral]

FACT: The go-to devices for +/-9 volts from a 9 volt supply and +18 volts from a 9 volt supply in stompboxes are MAX1044, TC1044, LT1054 etc...........

I was just re-reading some old threads I'd bookmarked and this caught my attention:

Hello Rick, for making a negative voltage using a 555 timer, have a look at:

http://www.circuitsonline.net/circuits/view/139

Should be good for up to 30 mA, which should be enough for negative biasing, I suppose. 1N4148 should work, according to the text: will give you a slightly higher voltage (-11,8 or so, I guess). You could add two voltage multipliers to this to get to to -36Volts (or even closer to -33 when using 1N4148's). Just observe polarity of diodes and capacitors: should be directed opposite to your positive multiplier.
Maarten

Here's the voltage doubler link: http://www.circuitsonline.net/schakelingen/138/voedingen/spanningsverdubbelaar-met-ne555.html

.....and here's the negative voltage link: http://www.circuitsonline.net/schakelingen/139/voedingen/negatieve-spanning-met-ne555.html

The text is in Dutch, so you'll need to use Goggle's translation feature, but the schematics are in the international language of electronics.

Compared to a dedicated charge pump chip, the additional parts count is negligable, and the 555 is very cheap and possibly to most plentiful chip on the planet - and unlikely to go out of production any time soon.

I was actually re-reading that post to see if there is a way to get a negative voltage from a 555 already set up as an SMPS, I'll have to do some experimenting there.....

Maybe it's also possible to use additional voltage doubling stages to get higher voltages too?

So.........why are we using MAX1044, TC1044, LT1054 etc to do this job, and not NE555? I know there are issues with 555's crowbarring the supply - but this can be worked around pretty simply. Additionally, 555's are used in a few stompboxes already, eg, Crash Sync, Uglyface.

[gmoon]

Using a 555 for a negative supply definitely works; I build one 3 or 4 years ago for an 40x2 display LCD that required a negative reference. Not much current was required, of course.

I don't see why a doubler wouldn't work...

[frequencycentral]

Both the linked circuits run at around 20kHz, if whining occurs (like in an unboosted MAX, or an ICL7660) it should be possible to lower the value of the timing cap to get the 555 oscillating at a frequency higher than human hearing.

[synthmonger]

I'll get around to testing this out with my circuits this week. I tried using a 4049 that output +/- but the current draw was too much for it to handle and it worked very sloppily. I wonder if CMOS 555 would be better to use.

[R.G.]

The 555 works fine as a driver for a doubler/inverter/pump. This has been a favorite dodge of the EE in trouble for another voltage at the last minute for decades. I once designed in a 555 to run a capacitive discharge auto ignition. You appreciate that this was before cars all came with electronic ignitions, right? 

The problem is that a stock 555 does not play well with audio. It produces current spikes on the power supply and ground leads when it switches that are quite difficult to keep out of audio circuits. This is why the CMOS 75555 is recommended every time someone tries to use a 555 circuit here and finds out that it ticks.

Getting it over 20kHz is a good start, but even then you can see aliasing back down to audio in some circuits.

The 555 is an amazing chip. It's been the electronic tinkerer's wonder for almost 40 years. But be prepared for those spikes.

[frequencycentral]

I just successfully added a -12 volt output stage to the 555 based SMPS I'm using for my submini tube amp experiments. Actually, just a touch under -12 volts, more like -11.7 volts. Just two 10uF caps and two 1n4148. That's cool! Now I need to add some more stages to it to get to around -33 volts to negative grid bias my 5902. Thanks maarten - it didn't sink in right away, but I'm on it now!

electronic tinkerer

For electronic tinkerer read monkey with a machine gun!

[frequencycentral]

Now I need to add some more stages to it to get to around -33 volts to negative grid bias my 5902. Thanks maarten - it didn't sink in right away, but I'm on it

Haha! Cracked it!

[frequencycentral]

OK, I just posted a schematic for a SMPS with a -33 volts charge pump section: http://www.diystompboxes.com/smfforum/index.php?topic=74088.msg661075#msg661075

What I want to do now is to develop a 555 charge pump with multiple doubling sections delivering around 80 volts. So far not so good - just fried a 555.    Any suggestions?

[puretube]

This??? 

[frequencycentral]

This??? 

Yeah - but how to add more +ve stages?

[R.G.]

Yeah - but how to add more +ve stages?

Google "%^&*croft-Walton".

[maarten]

Hello Rick,
have a look again at the link Renegadrian provided - http://w1.859.telia.com/~u85920178/power/vconv_01.htm. I am curious to learn what a negative bias will do to the 5902, currently I am still enjoying experimenting with just cathode bias. This works fine for me, even though it is an SE amp, it still puts out more noise than my family cares for.

Let me know if you need some help with the dutch text - I picked up some knowledge of this along the way...

Maarten

[Cliff Schecht]

Yeah - but how to add more +ve stages?

Google "%^&*croft-Walton".

Gotta love that autoedit. The C0ckcroft-Walton multiplier is a nifty little circuit. It's an inexpensive way of deriving negative and high voltage supplies without taking up a lot of board real-estate (IC based designs still need those big caps!). More inverters used equals more drive capability too, which is nice to know when you're "HV" line starts sagging under load .

[earthtonesaudio]

You could also replace the inductor in your switcher with one side of a transformer.  If the other side is center-tapped, you can get symmetric + and - high voltages out.  Just be mindful of the current going through those windings (i.e. cut power if you smell burning).

[Cliff Schecht]

If you're trying to supply any amount of current then that is pretty bad practice. Typically one goes through a whole process of laying out the specifications for their switcher design before you start and part of the process is calculating things like inductance (Volt-seconds per amp), number of turns, wire size, winding area of the core, required magnetic flux density and permability of the material and the temperature rise of the core. This is all for a disconinuous-mode flyback supply.

Now, a discontinuous boost supply is VERY similar design-wise to a discontinuous flyback and the conversion from one to another isn't all that complicated, but there are a lot of factors that one needs to take into account to make a truly safe and reliable supply. Throwing in a random transformer will probably work if the inductances and ratios work out correctly but you're going to have a pretty lossy supply that probably won't be able to deliver its full load current. Also, you want to avoid accidentally making a continuous-mode boost supply (current control) which has a right-hand plane zero that is impossible to completely compensate for. If one ends up accidentally in continous mode with their boost supply (inductor current never goes to zero) then you're going to have a very unstable power supply as there is excessive phase shift in the feedback loop (aka you have an oscillator instead of a regulated supply).

[frequencycentral]

What I want to do now is to develop a 555 charge pump with multiple doubling sections delivering around 80 volts. So far not so good - just fried a 555.    Any suggestions?

Yeah - but how to add more +ve stages?

Google "%^&*croft-Walton".

I think I confused myself yesterday doing the negative charge pump first, all those wrong-way-round caps and diodes. I'll take a fresh look later this week. It should be easy.....

[frequencycentral]

What I want to do now is to develop a 555 charge pump with multiple doubling sections delivering around 80 volts. So far not so good - just fried a 555.    Any suggestions?

Yeah - but how to add more +ve stages?

Google "%^&*croft-Walton".

I think I confused myself yesterday doing the negative charge pump first, all those wrong-way-round caps and diodes. I'll take a fresh look later this week. It should be easy.....

Should this work? I haven't got the opportunity to breadboard it for a few days...............

[earthtonesaudio]

It's gonna be a lot of work for the 555 to charge up 60uF (all those 10uF caps in parallel) initially, but after that I don't see why it wouldn't.

If the 555 can't handle it, you might try adding some buffers or converting part of the cap section to series (at the cost of increased ripple).

[rustypinto]

What I want to do now is to develop a 555 charge pump with multiple doubling sections delivering around 80 volts. So far not so good - just fried a 555.    Any suggestions?

Yeah - but how to add more +ve stages?

Google "%^&*croft-Walton".

I think I confused myself yesterday doing the negative charge pump first, all those wrong-way-round caps and diodes. I'll take a fresh look later this week. It should be easy.....

Should this work? I haven't got the opportunity to breadboard it for a few days...............

Rick did you get this or the inverter working yet?

I just breadboarded a bipolar 555 timer and its very noisy and unregulated. In a voltage inverter topology, i was able to see -13V to -4V over a 0-70mA load. RG's comments about spikes were definitely true, there was lots of clock bleed through when i powered an opamp. I also measured a lot of spikes on the 9V and generated negative supplies. I'm gonna try the CMOS version tonight.

[frequencycentral]

I was able to add a -33 volt charge pump output to a 555 based SMPS, which I detailed in this thread (halfway down page 6): http://www.diystompboxes.com/smfforum/index.php?topic=74088.100

I had a couple of stabs at using a 555 as a charge pump for positive voltage doubling with multiple doubling stages, but didn't get it completed before (as usual) I got sidetracked by another project.