Electronics > Beginners
PWM for LM317 - how to increase resolution?
joeyjoejoe:
Regarding the LM317, I did put a 400ohm resistor on the output for now for testing purposes so I have a minimum load - gives ~12mA load. The regulator seems to be working well with just the buffered PWM input.
I'm going to apply some of your ideas for scaling and see how that works out - I will try it with the LM358 as a buffer for fun, but I am wondering if I could ditch it all-together.
Definitely appreciate this feedback, I will give it a shot tonight! :)
Zero999:
--- Quote from: joeyjoejoe on August 28, 2018, 02:58:38 pm ---Regarding the LM317, I did put a 400ohm resistor on the output for now for testing purposes so I have a minimum load - gives ~12mA load. The regulator seems to be working well with just the buffered PWM input.
I'm going to apply some of your ideas for scaling and see how that works out - I will try it with the LM358 as a buffer for fun, but I am wondering if I could ditch it all-together.
Definitely appreciate this feedback, I will give it a shot tonight! :)
--- End quote ---
The previous circuit I posted will not work with the LM358. It is designed to work without any buffering and relies on the impedance of the potential divider to form the lower resistor to set the minimum output voltage for the LM317.
joeyjoejoe:
Noted, thanks!
With this scaling, might even get away with 8-bit PWM, as that will give me about 6mV (1.5v/255) per step. Plenty of resolution!
joeyjoejoe:
Wow, totally works! Thanks so much for all your help, this gives me plenty of resolution to work with.
Next, ADC's, reference voltage, current sense shunt...
joeyjoejoe:
So update on this, it's working GREAT! With some smoothing I'm really able to control this thing - it takes about 80% duty cycle to hit 4.20v, although some cells are 4.3 or 4.35v so I might tweak it slightly. For now, good enough!
I've cooked up another thread on getting a 5V reference going so I can continue the project! Thanks again for your help on this.. I still need to keep re-reading what you've put down to get it figured out :)
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