Controlling Variable Voltage Regulator L200 or LM317 Using PIC Microcontroller?

Finally PWM output via low pass filter given to LM324 and i was able to get upto 0-23V per step 0.5Volt increment it worked......Thanks...guyz.....Special thanks to Fragrance for the designs....Reference.. The output of the LM324 can be directly connected inplace of Variable of LM317.

manishanand14 said:

Hey kripacharya!


Can you tell me the part no. of some generic digital non-volatile potentiometers for this purpose.

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from analog device the best is ad8402,03,04




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asking said:

Finally PWM output via low pass filter given to LM324 and i was able to get upto 0-23V per step 0.5Volt increment it worked......Thanks...guyz.....Special thanks to Fragrance for the designs....Reference.. The output of the LM324 can be directly connected inplace of Variable of LM317.

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if you don't mind can you share it here for other user benefit

regards
Fragrance

yes surely i would be updating the circuit diagram...

asking said:

yes surely i would be updating the circuit diagram...

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R2 IS 220R NOT 120R PLEASE MAKE SURE...

asking if your using this as a power supply I would recommend you add some sort of current limiting in your software so if the unit under test as a short or draws to much current shut of the PWM to your op-amp. It's not good when your freshly built design goes with a bang or a puff of smoke.
You have made good progress and it would be a shame not to make it a better design

wizpic said:

asking if your using this as a power supply I would recommend you add some sort of current limiting in your software so if the unit under test as a short or draws to much current shut of the PWM to your op-amp. It's not good when your freshly built design goes with a bang or a puff of smoke.
You have made good progress and it would be a shame not to make it a better design

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Yes Dear,

Work is under progress...this topic was just how to control digitally LM317, Complete prototype would take a little longer....will update with the best but for now this is basic idea how to control adj pin of LM317 digitally using microcontroller

asking said:

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R2 IS 220R NOT 120R PLEASE MAKE SURE...

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interesting circuit. However here's some thoughts i had --

1) why do you need the R2 resistor at all ? It serves no purpose except to feed an additional fixed current into the opamps output. The output of the LM317 will simply be Vadj + 1.25v always

2) your opamp uses strange resistor values, is setup as non-inverting with a gain of 5. I suppose so that 5x5=25 which is above your max desired voltage. You could use any combination of R3, R4 for this gain. Or even a slightly different gain (use PWM period mods to get your step size & voltages correct).

3) The lm324 with a +24v supply might have difficulty reaching (23 - 1.25v = 21.75v). You should design for a bit more headroom.
3a) similarly the lm317 needs more than ( 24-23 = 1v) differential to operate properly at the high end.

4) since the lm317 is simply behaving as current amplifier with voltage determined by its Vadj pin, why not simply replace it with a higher power NPN bjt? As in all conventional power supply designs ? Additional benefit is the the Vbe drop is smaller too, and you can get better current output.

5) as is, the output ripple will be as bad as 4x the residual ripple on your pwm RC filter and no better.
5a) you could use a small cap on the opamp output, and take advantage of the cap-multiplier effect. As long as the voltage changes are not too fast, the opamp should be able to handle it... maybe add a current limiting resistor.

6) on the lower end, i don't see how you achieve 0v (??). Lm324 output can go close, but not exact 0. But worse .. don't forget the 1.25v addition by the lm317 ! You could use some strategic diodes to offset this...

Fragrance's schematic in post#17 does all of this...

1) why do you need the R2 resistor at all ? It serves no purpose except to feed an additional fixed current into the opamps output. The output of the LM317 will simply be Vadj + 1.25v always

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I stumbled upon the same thing at first sight. But a minimum load current is required according to LM317 specification, otherwise the output voltage might rise above intended value. The current must not necessarily be sunk by the OP, however.

See R2 is necessary as per their Datasheet it should be ideally 220R or 240R. This circuit which i designed is just the driver. Actually m using it with TIP35 Pass Transistor to get 15-20AMP Output and it works fine i tested it with 30 minutes on continous load @ 5amp. Output i am getting is 22-22.5Volt maximum output. Input voltage is 24.54Volt.

Actually all of your points might not be verified by me...but i tried BJT as you refered...but it jumps variable form 5v to 9v and 18 to 24v i donno why...so i used op-amp and i got what i was needed. Actually i have driven 12V Halogen Lamp so i might not be very precise about each reading.......

About the Output Ripple, i have fixed 50V 4700uF Cap...and output is pure....without any ripples. This is the simplest and low cost design till now...Further modification as mentioned above are really useful for future upgrades...

take idea from this and improve your design

Thanks for you design reference...will check and make the best out of it