Electronics > Beginners

LM317 Based Digitally Controlled Power Supply

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TerrySt:

--- Quote from: Zero999 on April 23, 2024, 06:47:34 pm ---I'd just ditch the LM317 and replace it with an emitter follower. I chose the BD437 because it has a high enough hFE to be driven by the LM358, even with a collector current of 1A.

It's designed so neither op-amp gets driven into saturation, which can take awhile to recover from. D2, R8 & R9 form another feedback loop when it's in current mode. This limits the voltage over-shoot, during recovery.

The peak current due to the speed limitation of the current op-amp is limited by D3 and D4 which clamp the base voltage to around 1.4V above the output.
(Attachment Link)

--- End quote ---

That looks like a good approach.  Many ways to go about this for sure.  I like the way the voltage control sums with the current control.

I added models for 'real' op amps to my version and tweaked the component values to make it work with a range of output (load) capacitance (up to at least 10,000uF).
I'm posting the latest.  It could still use some fine tuning, but since the OP hasn't been back, probably no reason to carry this further.

Terry

TerrySt:

--- Quote from: MrAl on April 24, 2024, 01:23:38 pm ---
Hi there,

Actually I was referring to the accuracy of the set point of the voltage that would be controlling the LM317.  If the user wanted to output say 5 volts then they would have to apply about 3.75 volts to the ADJ pin.  If it was just 3.70 volts then the output would be 4.95 volts.  If the design could get that right though (3.75v) I don't think there would be any worry, but that could easily require feedback which brings in the issue of control stability into the picture.  If the designer wants to use feedback then it's going to be their responsibility to get it stable.  That means the uC will have to sample the output and make adjustments, and that means there will be a delay.

As far as regulating once the right voltage is actually applied, that may be ok but I have not looked into that in detail.

--- End quote ---

Yep.  I hope the OP realizes the issue and has a plan to deal with it.

Terry

aliarifat794:
Here is also an adjustable power supply design featuring LM317 and LM337. You can see it for further improvement. It uses two voltage regulators, an LM317 for positive voltage and an LM337 for negative voltage.
https://www.pcbway.com/project/shareproject/LM317_AND_LM337_ADJUSTABLE_POWER_SUPPLY_CIRCUIT_BOARD_904eaf4a.html

EthannCraftt:
Thanks all for replying!! I got caught up in my high voltage work and was a little busy with that.

I'm not necessarily opposed to replacing the lm317 with discrete components, I just thought it would be a fun design challenge and a nice way to use the ones I had on hand ;D

I did plan on adding a feedback on the output to the microcontroller (and one across the 1ohm resistor from the current limiter circuit), I just didn't know how to integrate that into a digital schematic.

The main problem that I've noticed based on the replies was the fact that inputing a voltage puts the internal voltage refrence in series, and to be frank I doubt the accuracy of my own voltage input. How would I go about voltage regulation with PWM another way that doesn't have this issue? I couldn't figure it out with my tinkering in simulation software. Can it even be done while maintaining use of the LM317?

Again, I would be perfectly okay with changing out the voltage regulator with discrete circuitry, so long as it's accurate(ish). Thanks!

MrAl:

--- Quote from: EthannCraftt on April 26, 2024, 02:25:23 am ---Thanks all for replying!! I got caught up in my high voltage work and was a little busy with that.

I'm not necessarily opposed to replacing the lm317 with discrete components, I just thought it would be a fun design challenge and a nice way to use the ones I had on hand ;D

I did plan on adding a feedback on the output to the microcontroller (and one across the 1ohm resistor from the current limiter circuit), I just didn't know how to integrate that into a digital schematic.

The main problem that I've noticed based on the replies was the fact that inputing a voltage puts the internal voltage refrence in series, and to be frank I doubt the accuracy of my own voltage input. How would I go about voltage regulation with PWM another way that doesn't have this issue? I couldn't figure it out with my tinkering in simulation software. Can it even be done while maintaining use of the LM317?

Again, I would be perfectly okay with changing out the voltage regulator with discrete circuitry, so long as it's accurate(ish). Thanks!

--- End quote ---

Well it does make an interesting linear series pass power element as compared to a regular power transistor.

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