I'm participating in project of create small thermal calibration chamber. I would like to get to know this topic. At this point I know that peltier module will be driven by voltage not PWM. That's because of provide general stability of the system.

How I can create such circuit? I don't think about temperature sensor just microcontroller that drives this peltier module. Let's say that my stm32 doesn't have DAC. Do any digital volrage regulator exist? Would it be nice to use adc and then drive voltage regulator or opamp? Do voltage regulator would be sufficient for peltier module?

 

STM32 MCU has DAC.
If you do not wish to use DAC you can use PWM and an integrator.
You can also use digital outputs and resistors to create a DAC.

 

I have heard conflicting information about using PWM to control a Peltier device. But the document seems to cover it quite well.

Peltier FAQ

AsI read it, if you use a PWM voltage of Vmax, use a single sided driver so that the Pletier does not operate a a generator during the off portion and use at least 2KHz frequency, PWM is a good method of controlling Peltier performance.

 

That's because of provide general stability of the system.

How stable do you need?

There are many kinds of "PWM".
One kind, say you want 5 degrees. It turns on/off at 5/6 degrees. So it turns on/off every couple of seconds.
Another kind will run at 100% duty cycle until it is very close to temp then drop the on time back to hold at temp. It might be turning on/off 1000 time a second.

 

Ron, check out the doc I linked. Turning the current on and off at a low frequency creates thermal stress. Using a higher frequency and having it operate at that frequency continuously would be better.

 

I just read that PWM is less efficient than using DC. This problem is not important to me because it only happens near 50% and not near 0 or 100%.
I had not though about thermal stress. I think if you hold the cells to within 2 degrees there will not be much stress.

 

Thank for your answers. I'm using DC to control a Peltier device, so linear drive. Then I will pick up a proper microcontroller with dac.

How stable do you need?

The best I can. It a student practice project.

 

My temperature chamber has a low cost thermostat that holds to +/-1 degree. No micro.

 

Do voltage regulator would be sufficient for peltier module?

Need to know the maximum current and voltage the Peltier requires.

 

I have found out a lot from your answers and document. I will talk about circuit and Peltier with employer. At this point, I have no knowledge about details. I hope he will easy share his knowledge with me.

 

The Peltier is 100W. Is it possible to use voltage linear regulator? Would you recommend any?

 

Solved. We decided to use PWM instead of external programmable power supply or LDO.

 

does not operate a a generator during the off portion

Did you mean H-bridge can cause issues? (heat / cold option) What about the need of use LC filter on output? 8A is a quiet a lot for inductor.

 

What about the need of use LC filter on output? 8A is a quiet a lot for inductor.

Such inductor found on Digikey.
It is good for 32 kHz frequency.
https://www.digikey.com/en/products/detail/würth-elektronik/74437529203101/8134289?s=N4IgTCBcDaIOwBYEGY4FYwE4wAZkEYd8QBdAXyA

 

I'm participating in project of create small thermal calibration chamber. I would like to get to know this topic. At this point I know that peltier module will be driven by voltage not PWM. That's because of provide general stability of the system.

How I can create such circuit? I don't think about temperature sensor just microcontroller that drives this peltier module. Let's say that my stm32 doesn't have DAC. Do any digital volrage regulator exist? Would it be nice to use adc and then drive voltage regulator or opamp? Do voltage regulator would be sufficient for peltier module?

Hi,

Wouldnt you want to measure the temperature and use that as feedback? That's the best way in thermal systems. You can get the temperature to be nearly perfect and if it is a constant temperature, really really near perfect.

If you decide to measure the PWM itself, that's probably easy because you are generating the PWM. Just use a little math. I would think you might measure the current too though or at least create a calibration table to look up the current with a given voltage. Since the PWM peak is constant, this should be easy. And with that in mind, the PWM peak should not and need not go above that which causes the maximum current you will get that with the PWM duty cycle set to 100 percent.