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I am trying to control a 12V Peltier (6A maximum current, but I am unlikely to need to use anywhere near that) element with a 5V PWM supply (from an Arduino at the moment).

I am using a logic level MOSFET (IRLZ44N) to allow the 5V (low current) to control the 12V (high current) load. That seems to work ok and the MOSFET stays cool even without a heatsink.

One side of the Peltier is getting hot as expected. However, the other side is not getting very cold. I am given to understand that powering a Peltier element by PWM is not ideal, and a steady DC voltage would be much better.

My first thought is to use a low pass filter, however, I am having difficulty choosing the correct type and components to use.

As standard the Arduino produces PWM frequencies of 490Hz and 980Hz, although it can produce up to 65KHz with a bit of additional work.

Am I correct in thinking that a higher frequency would be better and make it easier for a low pass filter to smooth out the pulses? As long as the MOSFET can handle the higher frequency (I believe the IRLZ44N is for switching below 100kHz).

I have been told an inductive low pass filter would be best for this application, but I don't know how to choose the values for the resistor or inductor. I know they are dependant upon my desired cut-off frequency, but I don't understand how I should be determining that. I'd assume that I'd want as low a cut-off frequency as possible for a steady DC voltage? 1Hz? And then, I would also assume that I want a high value resistor, but that results in needing a huge inductor (several Henrys).

Please can someone tell me how I should be choosing these variables? Or should I be approaching this from a different direction entirely?

I have considered just turning the Peltier fully on/off for set time intervals but that doesn't provide a stable temperature and there is suggestion that it even damages the Peltier element.

Thanks.

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    \$\begingroup\$ A peltier creates a temperature differential, so if you want one side to be cold, you need to keep the other side from becoming too hot. Do you have a heatsink and/or fan on the hot side? \$\endgroup\$
    – Mattman944
    Jul 23, 2022 at 14:14
  • \$\begingroup\$ I don't really understand what that has to do with my question. When I actually start using it properly I know I will need to attach a heat sink. No I don't currently have a heat sink on it because it is not getting too hot (still cool enough to hold). I am just testing it at low power levels at the moment. \$\endgroup\$
    – Gravitate
    Jul 23, 2022 at 14:48
  • \$\begingroup\$ You need to go to high tens of kHz or your inductor would be ginormous. \$\endgroup\$
    – winny
    Jul 23, 2022 at 15:24

1 Answer 1

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If you add an inductor and a diode to your circuit you have a buck converter. The inductor value can be smaller at higher PWM frequencies, the relation is linear.
10 mH at 3A is a very big inductor, so try to produce at least 10 kHz. Even higher frequencies need a proper gate driver between the MCU and the MOSFET which adds complexity.
Play with the simulator and change the values of L1, C1 and V1 to see the effects on the output waveform.

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ Thanks. This is really helpful (although my trial is now over for today :(). If I set it to 9KHz (10KHz seems to break it), 5mH inductor, 100uF cap. it seems to produce, what appears to me to be, a fairly good result. \$\endgroup\$
    – Gravitate
    Jul 23, 2022 at 15:44
  • \$\begingroup\$ One question regarding the resistor... won't it need to be able to dissipate a significant amount of power - Approx. ~18W at peak? The Peltier element has an approx. resistance of 2 Ohms. \$\endgroup\$
    – Gravitate
    Jul 27, 2022 at 9:27
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    \$\begingroup\$ @Gravitate The resistor R1 is a placeholder for your Peltier element, not an extra component. \$\endgroup\$
    – Jens
    Jul 27, 2022 at 12:35
  • \$\begingroup\$ Hahaha. Sorry. I was being thick. That makes more sense. I don't know why but I was thinking it was in series with the Peltier. Thanks again. \$\endgroup\$
    – Gravitate
    Jul 27, 2022 at 14:46

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