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LM317 digital control

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Maobuff:
Im working on my own power supply project. I want to control output voltage of LM317 via microcontroller (PWM or DAC). Can some one help me with it?

jdraughn:
All the datasheets I have seen for the LM317 cover this. The schematic shows a few transistors which pull different value resistors to ground to change the output voltage. You could get 256 values with 8 transistors. Using a buffered DAC would give you finer control with less parts.

danadak:
One limitation of the DAC approach is the min output voltage of a LM317 will
be ~ >-1.25V, its reference voltage. On way of handling this is an OpAmp summer,
operating off split supplies, with 2 inputs, DAC and an offset you generate of 1.25V.


Regards, Dana.

Maobuff:

--- Quote from: jdraughn on May 19, 2016, 10:20:16 am ---All the datasheets I have seen for the LM317 cover this. The schematic shows a few transistors which pull different value resistors to ground to change the output voltage. You could get 256 values with 8 transistors. Using a buffered DAC would give you finer control with less parts.

--- End quote ---

Can you show a circuit for solution with dac

danadak:
Very simple. take the V output of the DAC and tie it to the LM317 ref pin.


Regards, Dana.

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