How can I control the heating and coldness of a peltier module?


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steveastrouk6 months ago

Use PWM control, but at high frequency, and well filtered.

What are you saying?

Are you saying, use PWM followed by a low-pass filter?

Or is this some kind of deal where the dynamics of the load kind of act like a low-pass filter, and if that's the case, then how fast, what range of frequency is, "high frequency", compared to the dynamics of the Peltier module?

Analog Technology (author)  Jack A Lopez6 months ago
Thank you very much for your answer. As I am not specialized in the temperature control field, I noticed that my colleagues have ever bought low-pass filter and TEC controllers, can you help me take a look at those products: http://www.analogtechnologies.com/High_Current_Low_Pass_Filter.html
http://www.analogtechnologies.com/tec-controller.html
I want to use these products for outdoor LCD panel.
Thank you again.

I agree with Jack. If you understand the function of the modules, you don't really need to buy them. If its for your own product, buying modules is a pain, because you are held captive by the manufacturer's desire to continue to make the part. We are stuck with an RTD module at work that used to be around $50, and is now end of life - and $500 !!

I also am not a specialist in temperature control, although I guess I could tell you what I think of the product pages you linked to.

The first thing is that the low-pass filter (LPF) does not have to be anything fancy. It is just a handful of inductors and capacitors. In fact if you look closely at the data sheet for the LPF you linked to,

http://www.analogtechnologies.com/document/ATLF20A...

the picture of the filter has a diagram of its circuit printed on top of it. It is this ladder shaped thing with four inductors {L1,L2,L3,L4} and two capacitors {C1,C2}, with the values,

L1=L2=L3=L4 = 2 uH = 2 microhenry

C1=C2 = 100 uF = 100 microfarad

And you know, that is the kind of thing that is so simple you could probably build it yourself, for a lot cheaper.

The Wikipedia pages titled, "Low-pass filter" and "Electronic filter topologies" can give you some hints for that.

https://en.wikipedia.org/wiki/Low-pass_filter

https://en.wikipedia.org/wiki/Electronic_filter_to...

Regarding the controller ICs you linked to,

http://www.analogtechnologies.com/tec-controller.h...

well, i dunno. These look like they'll do what say they'll do, according to what is said in the data sheets, and if these controller ICs have any dirty secrets, the data sheet is often the place where these secrets are revealed.

I'll just mention what jumps out at me.

For the temperature sensor it wants a 10K thermistor. Also the input for the target temperature is an analog input. So if you want some sort of digital interface, then that has to be done with another thing, a microcontroller with some analog inputs and outputs.

The fact that the output of this IC is an H-bridge is kind of interesting. That means it can push current through the Peltier module in either direction, for heating or coooling. Although depending on the application, it might be the case that the Peltier only ever wants current in one direction; i.e. the case when the thing it is attached to always wants cooling and never wants heating.

Yes. PWM and LPF, or the ripple causes the cell temperature to fluctuate too much. Bang - bang is very bad for the cell, and they fail in less than the warranty period....

The cell is almost a pure resistance, so the filter needs to be external. We use them in ultra-precision applications, so my experience is wildly away from most people's needs, but we end up with less than 1mV of ripple on the cells.

Thanks for clarifying that. I guess those Peltier modules like to be fed smooooooooooooooooooooooooth DC.

We get control down to less than 0.03 C, so yes, SMOOTH. However, its not too hard if the switching frequency is nice and high,

If you look at the datasheet of a peltier, power in = heat pumped.

So controlling its temperature starts with an adjustable or fixed thermostat to a control circuit.

After that depending on your need for precision a simple on at a certain point off at a certain point, a thermally controlled PMW, or a thermally controlled regulator.

CP40.pdf283 KB

Details would be nice but a circuit as simple as this will control the temperature of your peltier.

Answer 4.bmp

I would use a thermistor and a comparator circuit to turn the peltier on and off.

The same system used to turn on and off a cooling fan with a relay for the high currents of a peltier.