Single PWM input signal to H-Bridge DC/AC inverter

Question

Im attempting to follow some of the multitude of h-bridge designs out there to create an inverter using power mosfets. While I can get the circuit to invert the polarity using the design in the first answer here: H-bridge - concern about mosfets, I'm only seeing .2v coming from a 24v supply. (I'm using IRF1405PbF n-channel and SUP53P06 p-channel fets) - from what I've read I'm not saturating them properly so they get hot and don't fully switch.

The outcome I'm after is to convert a DC voltage to AC at a higher than 50hz frequency in order to drive some Christmas light strings that have half the leds in each polarity without flicker.

Could anyone point me to a bridge schematic that would allow for a single PWM input (to control freq and most likely provided by a rasp pi). Or, anther way to generate a greater than 50hz AC supply from DC at around 24-30v/5A?

Answer 1

While not a direct answer to your question, you should look into the IRS2453. It is a self-oscillating full bridge driver with built in gate drive. You can set the switching frequency with just a resistor and cap. Pretty easy to use. Adjust frequency with a variable resistor or the like.

Otherwise, if you want to use the RasPi, you can take a single GPIO and put that into a NOT gate and a buffer. The NOT output would go to one pair of FETs and the buffer to the other. I would suggest using gate drivers to speed up the turn on times in this case. This way requires 3 to 4 ICs instead of just 1.

I'd suggest the first option as the second will not have any dead time between switching and is therefore more likely to have shoot through issues. If "faster than 50 Hz" means 100Hz or something then you should be fine either way.

Just remember, if the voltage you're switching is higher than the voltage you're driving the top FETs with, you'll need a high side driver to actually get the top FETs to turn on. The IR2110/2113 does high and low side switching but you'll need 2 of them to do all 4 FETs.