I have a temperature controller (Chino DB1000) which has a PID output of 4-20 mA. With this, I want to control the current going to a Peltier thermoelectric module (15V, 6A).
I am doing this via an ON-OFF circuit with a DC solid state relay, a 15 VDC power supply, and a temperature controller for SSR. But I don't want to keep doing this since the ON-OFF is not good for the thermal control or for the Peltier itself.
Is there any simple circuit to convert the 4-20 mA from controller to a regulated current to the Peltier? The 4-20 mA are not the sensor signal, but the processed PID control signal from the controller
After searching similar questions, I think that the answer might be towards PWM or MOSFETs.
Thanks a lot!
Best Answer
When you PWM a peltier you run an already relatively low-efficiency device at an even lower efficiency. The heat pumped across the peltier is \$\propto I_p\$, while the losses due to joule heating are \$ \propto I_p^2\$, namely (\$ I^2R\$).
If you don't need to run your peltier at its peak efficiency for your application PWM is a much simpler approach.
You will have to decide if you wish to have a bi-polar output, namely source/sink current or uni-polar where it just sources current in one direction proportional to your 4-20 mA control signal.
A 4-quadrant programmable power supply like some of the Kepcos is one approach.
An LED constant current driver with a dimming input would be a lower cost approach.
Of course you can design a full custom amplifier with a bipolar output stage, or run the peltier as a bridge-tied-load.
EDIT:
If you go the pwm route, a sample PWM modulator LTC6992 simulates directly in LTSpice, and has a component configuration to make life easy.