I'm trying to make 3 PWM circuits to control 3 different thermoelectric coo lers (peltier cooler)
I'm aware that ideally you shouldn't run these with a PWM, that's fine, and I'm only using these in one direction, only as a heater.
So I made a simple PWM, with a Linear Tech. PWM part, a high side FET drive r and a FET.
and the thing works ok for 1 heater, but once I plug three in... it goes ba nanas. Basically it looks like the PWM signal from one heater couples on to my rails somehow and then starts to impact the other heaters... I'm not ex actly sure if that's what's happening, but they defeintely don't play nice together, once I plug two in the PWM goes all out of what, bascially become s super sensitive and almost floats up to 100% duty cycle when I touch the potentiometer
My circuit is on the link below
My circuit is that image 3 times, all common grounds throughout
I've thought about
- Increasing my gate resistor to the FET
- Instead of taking my control signal from the rail take it from a voltage reference (TLV431)
- Increase my input voltage control from 1V to 5V (it's an option on the l inear chip)
- I don't want to, but maybe add isolated supplies?
- OR maybe I should buffer my control signal?