Switchable PS

kiltro · Post by **kiltro** » 15 Feb 2023, 16:01

Hello,

I'd like to desig a PS for my pedals.

Apart from the usual 9V outputs, I'd like a swtcihable 9-18V (9-12-18V).

I was wondering what's the most efficient way to do this. I was going with the usual variable regulator, but at 9V it would have to dissipate 9V...

Is there any better way? Multiple secondary transformer maybe?

FiveseveN · Post by **FiveseveN** » 15 Feb 2023, 16:08

https://en.wikipedia.org/wiki/Buck_converter

kiltro · Post by **kiltro** » 15 Feb 2023, 17:13

FiveseveN wrote: ↑15 Feb 2023, 16:08 https://en.wikipedia.org/wiki/Buck_converter

Forgive my noob question... wouldn't that make it very noisy?

plush · Post by **plush** » 15 Feb 2023, 17:29

kiltro wrote: ↑15 Feb 2023, 17:13
FiveseveN wrote: ↑15 Feb 2023, 16:08 https://en.wikipedia.org/wiki/Buck_converter
Forgive my noob question... wouldn't that make it very noisy?

Properly designed switch-mode converter can have as little noise as a linear power supply, or even less.

kiltro · Post by **kiltro** » 15 Feb 2023, 21:04

Nice, but not so easy probably.

So the switch would activate or baypass the converter, right?

FiveseveN · Post by **FiveseveN** » 16 Feb 2023, 06:59

kiltro wrote: ↑15 Feb 2023, 21:04 So the switch would activate or baypass the converter, right?

And feed your pedals the unregulated output? Have you thought this through?
Google says About 2,920,000 results for "adjustable DC buck converter", and as far as I can tell most are adjustable. There are many many chips to choose from, which is why I've kept it vague: you'd have to pick whichever suits your voltage, current, efficiency, noise, frequency etc. requirements.

plush · Post by **plush** » 16 Feb 2023, 07:20

kiltro wrote: ↑15 Feb 2023, 21:04 Nice, but not so easy probably.

Quite easy, actually.
You'll just need to invest a couple of hours for your research and use automatic calculators, such as TI Power stage designer tool.
Most of the stuff has already been done for you.

phatt · Post by **phatt** » 16 Feb 2023, 10:21

Hi Kiltro,
An LM7809 would have no trouble dropping 9volts, They are rated up to 1Amp. FWIW, I use a Laptop power supply which delivers 19VDC at 4Amp and then use an LM7809 for the lower voltage pedals.
IIRC I just added a series 220R resistor before the Reg chip and a small heat sink to be on the safe side but it only runs warm.
My Pedal board is silent and has run flawlessly for the last 6 years.

Phil.

kiltro · Post by **kiltro** » 17 Feb 2023, 12:57

Thanks Phil

Fender3D · Post by **Fender3D** » 17 Feb 2023, 17:40

LM317 just need swapping 2 resistors...

ansil · Post by **ansil** » 22 Feb 2023, 01:11

Perhaps I am unclear were you wanting to be able to switch this for all the outputs or do you want it To have 3 separate taps.
Depending on how much current you are looking for have you thought about using an old laptop power supply one that actually has a transformer in it.
I have an old gateway transformer power supply 19 V 6 amps.
It seeds a small circuit board that has a few 78L05s On it. I also have a 15 Volte line. But I'm just using a zener diode and the cap.
Now keep in mind I did choose this particular power supply so it could run my entire pedal board including charge my ipad, But also because of its really clean output on the Oscilloscope.
Really it is overkill but I had a lot of projects I was powering back in the day. Ipad single ended computer, And monitor. As well as a small amplifier that I built.