1590A/LM7809 regulated power supply

[Plexi]

Hi forum!

Last week my sister give me a 12v @1A switching power supply (wi-fi router).
My idea is to build a functional power supply, since my old DC-Brick is fully feed pedals almost all the time.
- 4 regulated 9v outputs, from 4x LM7809 regulators.
- 1590A enclosure that I've already purchased.


- D1/D2: 1N4007
- C1: 220/470uF
- C2/C5: 100nf
- C3: 100uf

My principal priority is the safety.
Any suggestion, advice, experience, etc, will be greatly welcome 

[bluebunny]

I can't see your picture from work, but by the list of components you wrote down, I would imagine it will be fine.  You might want to consider dealing with switching noise, though.  Wifi routers don't care too much about audible noise.

My principal priority is the safety.

Unless you rip your chest open and attach those 12V to your pericardium, you have no worries.  (And if you *do* rip your chest open, frankly a little 12V tingle is the least of your worries!  )

[Phoenix]

Don't need to use C2 or C4. C3 need only be 10uF for stability - making it larger serves no purpose.
You might also want a CLC filter on the input, as the 78xx series is intended for linear supply work - good rejection at 100-120Hz, but very little at the high operating frequencies of switch mode power supplies. Another good idea would be a reverse-biased doide on the output to protect against reverse voltage being applied to the output (center positive pedal with cap charged by battery or something is a possibility).

[greaser_au]

Don't need to use C2 or C4.

Standard electro caps usually have a bit of ESR at higher frequencies, so it's common to see a parallel monolithic or film cap anywhere from 10n to 1u used in certain applications.

In particular with this application, some of these regulators can oscillate, especially with weird loads (long pieces of wire, anyone?).  As per the datasheets it is good practice to include a film or monolithic ceramic right up nice and snug to the regulator on both input and output. 100n is as good a value as any.  The TI datasheet recommends 0.33u and 0.1u respectively.

I have soldered the monos directly to the pins a couple of times  

david

[antonis]

Plexi, maybe you're the only person I've seen drawing red line for negative supply... 

IMHO, D2 makes no sense..
(it comes right after full wave rectification and is simply added on previous possitive pair of diodes..)

I'm not sure if any OUT-IN over voltage could be be settled through LED/Current limiting resistor on time....

[anotherjim]

D2, R1, LED and C1 can be common to 4 regulators.
Keep 100nF at regulator pins - it will reject hf noise from the supply. Those router PSU's ARE noisy.
D1 doesn't need to dump current anywhere, only clamp any backward volts across the regulator at a safe value.
Agree C3 should not need to be too big - the circuits it's feeding ought to have RC filtering on power inputs - but we know many don't. Maybe compromise at 47uF?

- 4 regulated 9v outputs, from 4x LM7809 regulators.

Now then, it's a 1A supply and 7809 are self limiting at 1A each. You only need 1 regulator. 4 separate reg's won't reduce ground loop hum when they all have common ground. Might as well have only one 7809.
78L09 will limit at (what is it, 300mA?) which is better protection for the power supply and leaves 3 outputs working if one shorts out. I think the little L version would be better if you must use x4 regs. The 12v SMPS brick ought to have it's own current limit protection too, but can you be certain?

[EBK]

Just going to throw this reckless thought out there:
Many (most?) of the circuits we build for 9V will happily work at 12V....

[bloxstompboxes]

Just going to throw this reckless thought out there:
Many (most?) of the circuits we build for 9V will happily work at 12V....

Better watch out for those pedals with charge pumps who's IC uses 10V max before melting. But, yes, most others should be ok.

[EBK]

Better watch out for those pedals with charge pumps who's IC uses 10V max before melting. But, yes, most others should be ok.

That's one of many reasons I couldn't bring myself hit "Post" without adding "reckless". 

[Plexi]

Thanks everyone for your suggestions!

I can't see your picture from work, but by the list of components you wrote down, I would imagine it will be fine.  You might want to consider dealing with switching noise, though.  Wifi routers don't care too much about audible noise.

My principal priority is the safety.

Unless you rip your chest open and attach those 12V to your pericardium, you have no worries.  (And if you *do* rip your chest open, frankly a little 12V tingle is the least of your worries!  )

Sure..!
That's what I think too: I have in unused one 9v switching power supply because of noise. There's no cap or filter to save it: maybe it's dying.
No problem, the safety is for my pedals :-) (says the man that received 220v from christmas lights...)

Don't need to use C2 or C4. C3 need only be 10uF for stability - making it larger serves no purpose.
You might also want a CLC filter on the input, as the 78xx series is intended for linear supply work - good rejection at 100-120Hz, but very little at the high operating frequencies of switch mode power supplies. Another good idea would be a reverse-biased doide on the output to protect against reverse voltage being applied to the output (center positive pedal with cap charged by battery or something is a possibility).

Great!
Usually I use the reverse voltage diode protection on 9v input on pedals, but will be good here.
I'll search for any CLC Filter; I think I have one of those in my Miscellaneous disassembly drawer (pc monitors, tv's, pc power supply's, etc).

Don't need to use C2 or C4.

Standard electro caps usually have a bit of ESR at higher frequencies, so it's common to see a parallel monolithic or film cap anywhere from 10n to 1u used in certain applications.

In particular with this application, some of these regulators can oscillate, especially with weird loads (long pieces of wire, anyone?).  As per the datasheets it is good practice to include a film or monolithic ceramic right up nice and snug to the regulator on both input and output. 100n is as good a value as any.  The TI datasheet recommends 0.33u and 0.1u respectively.

I have soldered the monos directly to the pins a couple of times  

david

I'll keep c2 and c3, and reduce c4.

Plexi, maybe you're the only person I've seen drawing red line for negative supply... 

IMHO, D2 makes no sense..
(it comes right after full wave rectification and is simply added on previous possitive pair of diodes..)

I'm not sure if any OUT-IN over voltage could be be settled through LED/Current limiting resistor on time....

I want to keep it "original" 
Should I move the LED after the regulator?

[Plexi]

D2, R1, LED and C1 can be common to 4 regulators.
Keep 100nF at regulator pins - it will reject hf noise from the supply. Those router PSU's ARE noisy.
D1 doesn't need to dump current anywhere, only clamp any backward volts across the regulator at a safe value.
Agree C3 should not need to be too big - the circuits it's feeding ought to have RC filtering on power inputs - but we know many don't. Maybe compromise at 47uF?

- 4 regulated 9v outputs, from 4x LM7809 regulators.

Now then, it's a 1A supply and 7809 are self limiting at 1A each. You only need 1 regulator. 4 separate reg's won't reduce ground loop hum when they all have common ground. Might as well have only one 7809.
78L09 will limit at (what is it, 300mA?) which is better protection for the power supply and leaves 3 outputs working if one shorts out. I think the little L version would be better if you must use x4 regs. The 12v SMPS brick ought to have it's own current limit protection too, but can you be certain?

Sure! C3 reduced to 47uf
You're right, but better prevent than lament 
Sorry my ignorance: only to limit and distribute? In which way they will for better protection?
I've already bought 4 LM7809's... my bad! I'll go for the smaller version, they aren't too expensive.

[rankot]

78L09 will limit at (what is it, 300mA?) which is better protection for the power supply and leaves 3 outputs working if one shorts out. I think the little L version would be better if you must use x4 regs. The 12v SMPS brick ought to have it's own current limit protection too, but can you be certain?

Not good, 78Lxx regulators have only 100mA output.

[Plexi]

78L09 will limit at (what is it, 300mA?) which is better protection for the power supply and leaves 3 outputs working if one shorts out. I think the little L version would be better if you must use x4 regs. The 12v SMPS brick ought to have it's own current limit protection too, but can you be certain?

Not good, 78Lxx regulators have only 100mA output.

Should I use 10 of them, to not "overheat" the 4 ones?

[bool]

See if you can make use of 78M09 version (note the "M" designator; "medium current" ... 0.5A).

[Plexi]

Sadly, where I live, I can only get the regular LM78.
With luck, and too expensive, some LM78L (mostly 78L05, for PT2399 delays)

Should I use the LM78 anyway?


Which filter can I use?

[anotherjim]

It's irrelevant if you don't have 78L's, but 4x100mA outputs can run a lot of pedals.

So use only one 7809 and have some spare? ...or carry on with x4 if you think you might be able to get a more powerful brick in future. It's just that x4 7809's can happily take a total of 4A which you will hope your 1A brick can handle without bursting into flames. It should protect itself properly - if it was supplied with a name brand router. Just that cheap OEM Chinese SMPS  have been known to catch fire - read about dodgy i-phone chargers!

You don't really need any inductors. Without knowing what they are you might build in instability/oscillation.  I would keep it simple.

[Plexi]

Sure.. I get it.
The power supply looks robust, and I didn't test it (I'll try with a reg in the breadboard to see if they produce noise).
Ironically the brand is "Ruidir", sounds similar to "ruido"/"ruidoso" in spanish, that means "noise"/"noisy"

I assume the 1A at the input will divide into the amount of regulators, feeding 0.25 to each one... am I right?
Will this increase/decrease, or the regulators will mantain it constant on each out?

After your comment, I made the improved version, follow the advise of @Phoenix.
Should I use there a fuse (1A/250v) instead inductor?
I saw that some people use a 33R in line with the input, before each regulator: this act as fuse?

[anotherjim]

A fuse would probably be the way a lot of commercial designs would protect. 1A slow blow might be best - a fast blow might act in haste.

The brick current will divide according to load on each output.
Say...
A takes 50mA
B takes 950mA
C takes 100mA
D takes 0A (not used)
Then total from the supply is 1.1A
The supply's 1A rating is exceeded while none of the 7809's are reaching their own 1A limit.

Something like 33R to each regulator will improve noise filtering of the capacitors. If they are low wattage, they "might" act as fuses. You will need to calculate the power dissipation at the current you want that to happen. Watts=I²R
*Strictly, the resistors should then be "flame proof" (ceramic coated) types*

[Plexi]

Ok...an update here.
Tested power supply with the noisiest pedal in the history of noise pedals: EHX Pitchfork with one LM7809 breadboarded, no filter or caps.
Zero noise, nothing, cero: leave it connected a few hours, no heat.

A fuse would probably be the way a lot of commercial designs would protect. 1A slow blow might be best - a fast blow might act in haste.

The brick current will divide according to load on each output.
Say...
A takes 50mA
B takes 950mA
C takes 100mA
D takes 0A (not used)
Then total from the supply is 1.1A
The supply's 1A rating is exceeded while none of the 7809's are reaching their own 1A limit.

Something like 33R to each regulator will improve noise filtering of the capacitors. If they are low wattage, they "might" act as fuses. You will need to calculate the power dissipation at the current you want that to happen. Watts=I²R
*Strictly, the resistors should then be "flame proof" (ceramic coated) types*

Great... thanks for the explanation!
Just when I was considering the 1/6 watt small ones
(sorry my ignorance)

[duck_arse]

I have a question which may prove unhelpful. if we have a transistor like the BC548, it is rated ~500mA maxx collector current and can be series-pass [?] wired to boost the current capacity of a regulator. can we wire say 3 transistors series-pass w/ one reg, and provide 3 outputs w/ higher current rating than the nude reg, or will we lose control of the regulation?