I am trying to design a H-bridge circuit for my project to drive a thermoelectric cooler (TEC). Basically, I am trying to control the TEC with a voltage source driven by PWM.
Now the problem is, I have a 5V DC source but my microcontroller (ESP8266) uses 3.3V logic. Since the space for components is limited, I would like to drive the MOSFET directly from the microcontroller.
I have built a circuit based on some things I have found on the internet but am not exactly sure if it is correct. The TEC I am using is expected to draw up to 1A at 1.7V (maximum); the MOSFETS I am using are ROHM RZR040P01TL (p-type) and RUR040N02TL (n-type) which are rated at 4A, have Vgs(th)~=1.3V and built-in GS protection diodes.
- Since I have never designed an H-bridge before, my first question would be about the design. Does it look like something that would work or I am missing something here?
- When I increased the PWM signal above zero, there was a high pitch noise coming from the MOSFETs. Is this something to be expected or does that signal an issue in the circuit?
I have tried sending low duty cycle PWM from the microcontroller (1-10%) which seemed to be working fine - while the MOSFETs were still buzzing, the TEC was working fine and there was around 0.4V voltage accross the terminals (which you would expect). However, when I increased the duty cycle to 20%, one of the N-type MOSFETs blew out.
I am guessing that this either happened because the MOSFET overheated or because I have done something horribly wrong in my circuit design.
I would appreciate some advice on building MOSFET H-Bridge circuits in general as well as some specific recommendations for this particular design.
I have redesigned the circuit to have each MOSFET switch separately as @WhatRoughBeast suggested. I also have added two N-type MOSFETs to control the P-type gates which should solve the voltage difference problem. This appears to have solved the noise issue - now buzzing only appears if I reduce the switching frequency to 5kHz or lower.
In the current configuration I am trying to control the direction and voltage by:
having B1 and B2 set to LOW, A2 to HIGH and PWM-controlling A1
having A1 and A2 set to LOW, B1 to HIGH and PWM-controlling B2
While the MOSFETs appear to be working now (as in not overheating and blowing up), it seems I have another problem - with 5V supply, whatever PWM duty cycle I use, the TEG always receives the full 4.5V (using 10-20kHz).