Easy circuit voltage split(s) using only regulators.

FirstSpear

Sep 13, 2014
5
I've got a power supply from a laptop. It's 20VDC, 2.5A. I intend to use it to power two 9V guitar pedals (Sounds daft, that - What, your guitar's got pedals?) Rather than fiddle about with dividers and other complicated stuff, I'm thinking of simply attaching two 9 volt regulators (inputV up to 35V) to the power supply's output, and off you go. Two, one for each output, in order to enable maximum current availability of the regulators. The Boss pedal's current draw is 55mA, the Behringer's is 30mA, so one each might seem excessive, but I don't know what other stuff I might want to drive in the future, and the regulators are cheap as chips, and, further, the protection provided within the regulators is worth having. Over-engineering is why steam trains still run while diesel models lie rotting in scrapyards, by gum.
It seems an obvious and simple approach, and I can't see a flaw in my logic, but is it too simple? Have I missed something?
I'm thinking of doing similar using multiple 5V regulators to supply charging to various USB devices using other power supplies or transformers; including a PC power supply I have doing nothing but gathering dust.
It seems to me that the only maths that need doing are the voltage and current additions - totals not to exceed the supply's output specs. Is that the case?
Seems too easy, though.
(I had to search online to find the current ratings of both devices as neither gave that information on the bodies. I've got a scanner - Canoscan Lide 30, and I had to write that in permanent marker on the underside because the model number was not printed anywhere. The same for my Sony Ericsson phone. Each time I needed the model number, I had to lift out the battery. Why? Tut, damn, blast and flip!)

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,507
Just connect up a single 9V regulator and power both pedals from the one 9V supply. This is not a problem because the current draw is so low.

For a 5V USB supply you would be better looking fora switchmode regulator because the higher current drawn by USB devices and the large differential voltage (20V to 5V means that there will be a lot of wasted power -- heat) if you use a simple linear regulator.

BobK

Jan 5, 2010
7,682
For a 5V USB supply you would be better looking fora switchmode regulator because the higher current drawn by USB devices and the large differential voltage (20V to 5V means that there will be a lot of wasted power -- heat) if you use a simple linear regulator.
And by the time you have done that, you might as well have bought a 5V USB charger for less money.

Bob

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,507
And by the time you have done that, you might as well have bought a 5V USB charger for less money.

True. I was actually contemplating suggesting this.

If you do a little due diligence you may find that these will operate from the 20V rail with no (or little) modification.

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Rich Grise, but drunk
R