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I am designing TEC controller which both COOL and Heat. This will be control with PWM from microcontroller. I have two questions:

Spec: TEC will be run between 6V-12V max current 2.5A

  1. What type of capacitor should I pick for both direction and why (Tantalum, Ceramic, Aluminum)
  2. Do I need both Inductor DCR and Capacitor ESR to be as low as possible.
  3. Do do you think below schematic works

schematic

simulate this circuit – Schematic created using CircuitLab

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    \$\begingroup\$ I'm going to be blunt and say that you don't need any filtering at all. Connecting the TEC directly to the controller will work fine. But feel free to convince me I'm wrong and that you need filtering. You will need to provide good reasons. \$\endgroup\$ Oct 28, 2021 at 15:36
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    \$\begingroup\$ A TEC isn't a motor, no magnetic fields generated or collapsing, no brushes arcing. So it's just the current in the conductors to the TEC being PWMed. No real need to filter that. Just twist the wires and run the traces together for good coupling on the power conductors and you should be good. \$\endgroup\$
    – Aaron
    Oct 28, 2021 at 15:52
  • \$\begingroup\$ There is couple document regarding using PWM vs constant current. Let take look at ti.com/lit/an/slua979a/slua979a.pdf?ts=1635385955344. "Using constant current is 39.2% more efficient than the PWM current." but at long term is different story \$\endgroup\$
    – Shahreza
    Oct 28, 2021 at 16:00

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I'm dealing with similar project and bumped into this question.

Yes, PWM filtering is needed, not only due to power saving, but also to avoid overstressing the PN junctions - large currents during raw PWM on-state heat device up quickly, while off-state lets it cool. Each of these phases introduce expansion/shrinking which leads to eventual cracks in ceramic. Thus you should strive to DC with minimum ripple.

The configuration you have drawn is called "bridge-tied load (BTL)". These are quite popular in class-D amps. And yes, it will work.

Since you are PWM-ing into inductor, it sees effectively DC for %duty_cycle. DCR thus burns power during on-state. Lower DCR should reduce losses in your filter.

As for low ESR - this "eats" the high-frequency noise (lets it pass through to the ground). It also affects ripple current.

I couldn't find the driver you are referencing (DCR8876), so no idea about switching frequency. LP filters are usually designed with a certain corner frequency in mind, this gives you values, which further restrict your choice of devices.

I suggest you have a read from SLAA701A which deals with LC filter design for class-D amps

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