Electronic – H-bridge/buck converter with negative and positive voltage range


as already questioned here, i am still working on peltier controllers.
For that I am using a stepper motor driver (h-bridge) with a low-pass LC filter and the peltier element behind, as Olin Lathrop kindly explained. It works like a charm and is great for what it is designed for.

The schematic for that (I will add that to my older post as well):
(made with circuitlab)

My problem is controlling temperatures close to the room temperature. By now, I have been using the h-bridge as a MOSFET only. That means I need to decide if the Peltier is going to cool my application, or heat it up.
Since the h-bridge is capable of reversing the current I am trying to design a circuit that can go in both directions. The capacitor C1 is an electrolytic capacitor, so negative voltages would blow everything.
I thought of using diodes somehow to detect current direction, but I am not really getting it.
Can anyone help?

Best Answer

I think you missed the point of the diode in Olin's original schematic. It was there to protect the bare MOSFET from the flyback effects of the inductor, and provide a path for the current to flow when the inductor is discharging its stored energy. To do that with an H bridge, you would connect diodes to the supply rails, but that is sometimes handled inside the bridge chip itself. Connecting a diode directly between the H bridge outputs is pointless — and potentially dangerous, as Andy pointed out.


simulate this circuit – Schematic created using CircuitLab

If you want to use large polarized capacitors in your filter, you just need to connect their negative terminals to ground. Each one will see only the correct polarity.


simulate this circuit