Small psu for MCU

[gbuilder]

I'm hoping to power a small arduino off the 20V linear supply in my preamp.
I'd like to supply the Arduino with regulated 5V, bypassing its internal regulator.

Initially, I planned to put another LM317 in parallel with the preamp supply, but I'm concerned that the voltage drop from roughly 22V to 5V will create an awful lot of heat, and just doesn't seem a sensible thing to do. Naturally the Arduino won't consume a lot of current, but it will need to drive a motorised volume control, so not totally negligible.

Is there a common way of doing this?
These days most consumer amps have micro controllers in. How do they create the low voltage supply off the high voltage transformenrs?

Many thanks!

 

[Samsara]

Hello.
They use step-down switching regulator.

 

[russc]

LM2596(HV) regulator boards available on Ebay

 

[gbuilder]

Great, thank-you. I wasn't too keen on having noisy switching regulators close to the audio signal, but I can't see another way of doing it. My enclosure does have a steel box in the corner which could house the digital board. Thanks very much.

 

[wealas]

You can always use several regulators in series to split the voltage drop.

 

[Samsara]

I think it's better to use OKI-78SR, you can find it at eBay or Amazon.

 

[gbuilder]

Good point Wealas, although the preamp is built in a small case not cut out for dealing with heat of the combined linear regs, even if they don't need sinking individually.

Hi Samsara, neat module! And available quite cheaply from RS as well. Are you recommending this based on performance benefit over for example the LM2596 mentioned above, or is it just because of the fixed output and convenient pin headers, and because it is quite a common part.
Many thanks.

 

[gbuilder]

Wealas, thinking again, it would be lovely to keep the whole supply linear so I might just knock up a series of LM317s and see how hot they get, and also make sure my smallish transformer is coping with the extra current draw.

 

[Samsara]

it just because of the fixed output and convenient pin headers, and because it is quite a common part.

Right.
For performance, check datasheet https://power.murata.com/data/power/oki-78sr.pdf

 

[wealas]

Can't you split the motor supply to a second circuit? You might be able to run it on 20v so no need for regulators on that circuit.

 

[gbuilder]

Can't you split the motor supply to a second circuit? You might be able to run it on 20v so no need for regulators on that circuit.

Yes, I think you are right. Motor driver is UTC BA6208, which can handle up to 18V, so can use a smaller voltage drop for this supply. Good suggestion.