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LM317 digital control
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Maobuff:

--- Quote from: ZeTeX on May 20, 2016, 05:00:34 pm ---Don't forget minimum load requirements (the circuit I posted covers that) , capacitors and protections. read very carefully the datasheet.
I don't think you need the op amp as a buffer because the adj pin is going to and internal op amp.
just because you got it working without minimum load does not mean it is stable, especially if this is your bench power supply you want to build it as stable as possible.

--- End quote ---
Yea but later I can use op amp as an amplifier to adjust output range of supply. Im planning to use MCP4821(DAC) which have output range of 0 to 2.048V, then i just amplify it to get a range of 0-10.75V (~5.25 gain). Which give me a output voltage 1.25-12V.
I put a 750Ohm dummy load in my test.

BTW can I use this circuit in my power supply for constant load?
ZeTeX:

--- Quote from: Maobuff on May 20, 2016, 06:32:32 pm ---
--- Quote from: ZeTeX on May 20, 2016, 05:00:34 pm ---Don't forget minimum load requirements (the circuit I posted covers that) , capacitors and protections. read very carefully the datasheet.
I don't think you need the op amp as a buffer because the adj pin is going to and internal op amp.
just because you got it working without minimum load does not mean it is stable, especially if this is your bench power supply you want to build it as stable as possible.

--- End quote ---
Yea but later I can use op amp as an amplifier to adjust output range of supply. Im planning to use MCP4821(DAC) which have output range of 0 to 2.048V, then i just amplify it to get a range of 0-10.75V (~5.25 gain). Which give me a output voltage 1.25-12V.
I put a 750Ohm dummy load in my test.

BTW can I use this circuit in my power supply for constant load?

--- End quote ---
Yes, you can use this circuit with slight modification to test a variable load.
C1 + R15 Is there for compensation, without them the circuit might oscillate.
https://www.eevblog.com/forum/projects/yes-another-dummy-load-%29/?action=dlattach;attach=59947;image
Maobuff:
This is my finnal design. IC is current control, VC is voltage control, I is measuring current.
What about heat generating from Q1 and Q2. I think for Q1 it is 1.2Ohm * Icoil^2 which is around 0.012watts.And for Q2 its (Vmax-1V)*I=(12-1)*0.01=0.11watts. From datasheet i get junction to ambient which is 150K/W. So Q1 get 1.8K hotter that ambient and 16.5K for Q2. Is it true?
Maobuff:
And here is my controller board
Kleinstein:
The analog part has a few problems: the OP does not like a 100 nF cap at it's output. So some additions are needed here, to alow the OP to drive such a capacitive load.

Turning of the supply to the regulator in case of over-current is risky. A inductive load might give quite some kickback and thus damage the regulator. So there should be some over-voltage protection, at least a diode from the input to main filter cap.

The way the current is measured is also not that great: the resistive divider introduces quite some error and reduces the already small voltage at the shunt. So errors are rather large.  To prevent the overcurrent turn off part to activate directly when turning it on, there likely need some filtering caps / delay. With a relay you also need to have this part to be latching - otherwise the relay will immediately turn on again.

The µC might need a crystal to reliably work with the UART. With some tweaking it works without if the temperature range is not to large. The 2 DACs would need separate latching / CS signals to give different outputs.
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