I've been looking into MOSFET bridge rectifiers, also known as "zero IQ" rectifiers, as a replacement for traditional diode-based bridge rectifiers.
Here's a simple example:
The benefit, of course, is that the MOSFETs don't exhibit a forward voltage drop like a regular diode does, allowing for significantly higher efficiency in cases where the current is high or the voltage is low.
The major limiting factor for higher power designs seems to be that you can't get MOSFETs with a Vgs(max) high enough to rectify voltages exceeding 80V or so. There are some control ICs that are designed to help with higher voltage rectification (e.g. LT4320, LM74670) but they too are limited to around 75V continuous.
My first thought to solve this issue was to clamp the voltage with zeners, but I ran into the issue that you can clamp the voltage on two of the transistors just fine, but when you try to do all four you just get shoot-through because the diodes provide a path directly across the AC input.
I also thought about using IGBTs instead, but they appear to also have fairly limited gate voltages.
Is there a way to solve this issue, either by designing around the gate voltage limit somehow, or by changing the topology?
Best Answer
This is based on Dave Tweed's now deleted circuit with 4 added diodes.
The diodes in series with the 10k resistors drive the FETs on only when Vmains is above V_DC_out for a given FET by Vf_diode + Vth_FET.
Diagram is a hacked about cut and paste version of Dave Tweed's diagram.
Dave Tweed said:
If you use, say, 10 V 400 mW zeners, they can handle an average current of 40 mA. 10k resistors let you handle around 400 V.
But pay attention to the power dissipation in the resistors, too. Larger values of resistance will dissipate less power, but they'll also slow down the switching somewhat.