I have an idea for a design which I'm curious to get some feedback on. Without worrying about support circuitry, consider the following MOSFET h-bridge:
My questions about this concept have to do with the behaviour and properties of MOSFETs:
- What are the consequences for power consumption and heat? My understanding is that most of the losses in a MOSFET occur during switching. If Q2 and Q5 are continuously conducting, does that mean that the losses mostly occur in Q1, or are the others effectively "switching" too, when the upstream supply is being switched by Q1?
- Similarly, what are the consequences for the timing attributes of the devices? Will the rise and fall times be just that of Q1, or is it the max of Q1, Q2, and Q5, or worse, some sum of them?
The specific application being considered is a class D amplifier, but I'm looking to understand these things better generally, as the principles apply to power supplies, motor controllers, etc.
Edit to add: The reason this design (if it works) would be particularly excellent for an amplifier is that the PWM for an amp must be 200kHz to 1MHz to achieve accurate sound reproduction, but the direction will only need to be capable of changing as fast as the fastest sampling rate (48kHz). A full-bridge design also enables building an amp with a single power supply.
This design is a way to sidestep the usual objection to full-bridge amplifiers, which is that it takes twice as many of the expensive, audio-grade FETs.