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I am a hobbyist and I'm trying to make a power supply that withstands a few amps load, that also has a slow turn-on and low ripple. I'm powering up an ESP32-Cam that's pretty sensitive to ripple and voltage drops, so after scavenging the internet for circuits and some documentation, this is what I came up with:

Schematic

Is this schematic going to work?

C2, C4 and C8 are tantalum caps, would that help with ripple?

Are the transistors properly wired?

I have seen some schematics with and without low 0.1ohm resistors coming out from the emitter

What is the reason of those resistors?

Should I add them?

I don't have proper knowledge on electronics, so any help or guidance would be highly appreciated! Thanks!

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    \$\begingroup\$ Have you simulated the circuit? There are freeware software out there (lots of -ares, sorry) that can help you simulate what you need. \$\endgroup\$
    – user103380
    Commented Jan 27, 2020 at 18:51
  • \$\begingroup\$ i haven't! what do you recommend? \$\endgroup\$
    – marsex
    Commented Jan 27, 2020 at 18:56
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    \$\begingroup\$ @KingDuken It's not going to matter much if the OP simulates and it doesn't do, as hoped. And since the OP "tinkered" with this circuit, who knows? The OP admits not having "proper knowledge," so the simulator will just be hunt and peck to the OP. Kind of like throwing mud at the wall to see if it sticks, or not. \$\endgroup\$
    – jonk
    Commented Jan 27, 2020 at 18:57
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    \$\begingroup\$ @marsex You can download LTspice for free. There may be other good, free simulators. But I don't use them, so can't speak for them. I think there's an LM317 in LTspice but it is shy on BJT models. You may need to search the web for them. And in any case, learning to use Spice (LTspice or another other one) takes some investment on your part. If you are in some kind of rush, you'll need to take a breath and and press hard on yourself. \$\endgroup\$
    – jonk
    Commented Jan 27, 2020 at 19:00
  • \$\begingroup\$ @marsex What does your 12 V power supply "look like?" Where is it sourced? Are you using a device or is it a transformer and bridge rectifier with capacitors? What exactly is it? \$\endgroup\$
    – jonk
    Commented Jan 27, 2020 at 19:02

1 Answer 1

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  • Yes it most likely work.

  • It doesn't make much difference in linear power supplies because you don't have much of ripple at the input. tantalum capacitors usually used for switching power supplies, where ESR matters.

  • The resistor on the emitter is to match the transistors. it's called fixed bias which you can read more about in here. and for this design you don't need it.

As a hobbyist who is also in the process of building a power supply based on LM317, I'll share some of my experiences:

Lab PSU, PCB design

If you are going to draw more than 1 A from the supply and as you mentioned for cam which is going to run 24/7, using linear power supply is really wasting energy and money.

I suggest that you use a switching power supply with high frequency and design a filter for it's output to reduce the ripple to minimum. and that is going to be another question.

Edit:

If you want to draw only few mA, you can simplify your circuit and remove the bypass transistor. LM317 can provide up to 1.5 A, just make sure it's installed on a proper heatsink.

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  • \$\begingroup\$ ohh very nice, thanks you for your input! \$\endgroup\$
    – marsex
    Commented Jan 27, 2020 at 19:23
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    \$\begingroup\$ I think you should reconsider your answer, now that the OP has told us that their 12V source is rated at 1A but they want "a few amps" out. \$\endgroup\$
    – Elliot Alderson
    Commented Jan 27, 2020 at 20:04
  • \$\begingroup\$ @marsex See the edit. you can also use LDO regulators which are more efficient than LM317 and produce less heat. \$\endgroup\$
    – ElectronSurf
    Commented Jan 27, 2020 at 20:22
  • \$\begingroup\$ thank you very much! The idea behind using transistors was to protect the regulator from miss usage and poor heat disipation. Ill check out some LDO regulators then. I'm sorry about the few amps thingy hahaha, ill be more specific from now on! \$\endgroup\$
    – marsex
    Commented Jan 27, 2020 at 20:46
  • \$\begingroup\$ @marsex Good luck with your project. \$\endgroup\$
    – ElectronSurf
    Commented Jan 27, 2020 at 21:04

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