simple
MAKE A PROPPER GATE DRIVE!!!!
I have said this time and time again abt the Power-electronic cct that are flying around this forum. They all have common problems and that is complete lack of gate-drive to the power-switch!
This isn't low-power infomation that is getting delt with here THIS is POWER, be it only a few watts its a damb sight more then the uW contained within a LOGIC on/off or analogue signal
To switch a FET in anger (ie with real current through it) take energy/power to do that job and THAT requires a decent GATE-drive. IT can be as simple as a BJT push-pull. IT NEEDS TO BE PUSH-PULL!!! not like what is in this cct
**broken link removed**
The gate-drive ( or the incompetance of) in this cct is its main problem! a 10k is used to turn-OFF the N-types as well as a 10k to turn-ON the P-types. That is HUGH!!!! you need a push-pull (with gate resistor of a few 100R) to enable the charge to be pushed into and pulled out of the FET correctly
Anyway enough of the RANT
What is needed: a floating gate-drive
required:
1x OPTO (6n137 are good)
1x isolated DC
C converter, NVU/C&D do fantastic very small DC
C converters at around 1W, they have 5Vin to +/-12V out, 12Vin 5Vout lots-o combinations
1x PNP BJT
1x NPN BJT
and the odd few resistors and capacitors.
So for the top two FETS you now have a floating gate-drive which you connect the isolated 0V to the FET-source and the output of the PUSH-PULL to the GATE, isolates/floating power via the DC
C, isolated/floating signal via the opto
All in all kids, think of the gate-drive.