Peltier with Mosfet - Heat Issues and Alternatives

Question

I'm interested in using a Peltier device in conjunction with arduino as a precise temperature controller. I've followed the example below and have switched out batteries with a 12v power supply. After switching to the power supply the temperature gradient improved but the Mosfet became scorching hot. Although you might be inclined to say throw a heatsink on and all will be well, the end use would be a compact solution that would not favor the use of a heatsink. Are there any design changes that could be made so that I can avoid this heat issue?

http://garagelab.com/profiles/blogs/how-to-use-a-peltier-with-arduino

Answer 1

You don't show the circuit, but it seems you are trying to linearly regulate the Peltier current. That is going to cause significant dissipation in the pass element.

A more efficient way is to use PWM, although the pulses need to be filtered so that the Peltier sees the average. I go into a lot more detail about this here.

Answer 2

You're probably using a MOSFET that does not switch on completely with the Arduino output voltage level. You need a MOSFET that is guaranteed to turn on 'completely' (guaranteed and low Rds(on)) at 3.3V or 5V or whatever your MCU is outputting.

If your MCU uses a 5V supply, you can use something like a IRLB8748PBF which has a guaranteed Rds(on) of 6.8m\$\Omega\$ at 25°C, so probably less than 10m\$\Omega\$ even hot. That means power dissipation (when 'on') will be less than 1.0W at 10A, so a small heat sink should suffice -- or if the Peltier only draws 6A, it should run cool enough to not require a heat sink at all (provided you don't switch it frequently).

If your MCU is 3.3V, you'll probably need to pick an appropriate SMT part to get guaranteed performance at Vgs =3.3V, few modern low voltage parts are made in the old through-hole packages.