Temperature controlled TEC PSU design help - Page 1
Forum section: electronics / projects

author: BitShard
author_rank: Contributor
timestamp: July 14, 2017, 10:57:03 am
content: Hi all,I'm trying to design a circuit with jellybean parts (with or without a microcontroller), that supplies power to a peltier unit used as a CPU cooler. I'm not particularly worried about maintaining a constant temperature, I basically just want to set up a circuit that has a temperature "floor", such that the temperature of the cold side doesn't drop below a certain point. (Read by a thermocouple/thermistor etc).I've considered some sort of op amp circuit, though I'd have to dig out my electronics books and dust them off, alternatively I could possibly overkill it by using a microcontroller. A secondary consideration would be to have a display showing thermocouple temperature and power draw.Can anyone guide me on this please?Thanks!

author: BitShard
author_rank: Contributor
timestamp: July 14, 2017, 05:33:15 pm
content: Sorry for the bump, I have some discoveries.Peltier units essentially need to be driven with a relatively stable DC source, so I guess the best solution would be some sort of controllable current source, from 0 - 6A, (0 - 12V).I could go the analog route and use a thermocouple + thermocouple amplifier -> voltage normalisation amplifier -> voltage controllable current source.Alternatively I could go digital, and use some sort of microcontroller to read the thermocouple and control the current source.In either case, I would need some sort of controllable current source, any suggestions?

author: MK
author_rank: Regular Contributor
timestamp: July 14, 2017, 08:50:25 pm
content: As the loop control does not need to be that fast you could use a well smoothed switching supply or a dc capable class D audio amp to power the peltier unit. but the switcher does need to be smoothed/low pass filtered quite well to stop any more than a few mV of ripple across it.

author: kony
author_rank: Regular Contributor
timestamp: July 14, 2017, 10:15:23 pm
content: Go search older threads about TEC controllers, there was already plenty of discussion about this. But basically it boils down to highres PWM and very low impedance push-pull stage followed by lowpass filter. You want reasonably low ripple in the drive current. You don't really want to drive it by linear CC source, it is horribly inefficient at its task as it is already. Off the shelf class-D integrated amps tend to get inefficient as they are designed for (sometimes order of magnitude) higher load impedances.You can try winging it around TL494 if you want to go MCU-less, second error amp used as foldback mechanism for overheating protection on the hot side.Thermocouple is bad idea for precision temperature control, stick with platinum RTDs.

author: ocset
author_rank: Super Contributor
timestamp: July 15, 2017, 08:26:44 pm
content: For peltier, id just do two current regulated buck converters, each one able to push current in one direction through the peltier element.Activiate whichever one when you need to.(Also As you know, usually we dont care how cold our CPU gets, the colder, the better, usually)I take it you are doing analysis on CPU temperature though.

author: BitShard
author_rank: Contributor
timestamp: July 16, 2017, 04:37:21 pm
content: The temperature floor is to avoid condensation, not because I'm worried about the CPUSo this is going to be powered from a 12v rail off of the computers PSU, and the max voltage for the peltier is 15v. Would my best bet be to use a boost converter to get the voltage up to >20V, then use some sort of voltage/I2C/SPI etc controllable buck converter?