100A pulsed constant current regulator

[George]

I'm wanting my PIC to send out pulses which will be regulated to drive 100A output for a laser diode bar. I'm thinking about using maybe an IRF1405 FET (169A continuous @25C or 680A repetitive pulse ) driven from an opamp using the PIC to trigger a transistor which will supply a voltage divider ( with an adjustment pot ) on one input to the opamp and have the other input driven through a sense resistor inline with the load and FET.

My concern that the input capacitance may be slightly too high for the opamp to drive (5.5nF) effectively pulsed. rise and fall times are quite long with this FET also, around 200ns. The pulses I'm looking at giving it will be at shortest around 5ms and longest around 50ms. (in theory the rise fall time is only 0.01% the duration of the shortest pulse if the gate is pumped with 10A so expect 300X that with opamp supply of 30mA? If that's correct rise and fall would be around 2.5% of the shortest pulse.)

Even if I drive the FET with a driver, the regulation circuit would still take that time to stabilize.

Does anyone have a good solution to supplying this large amount of current regulated with pulses from the PIC? Any advice would be greatly appreciated. Thanks

[George]

am actually thinking now I may run continuous which will mean less drama for the turn on/off times - but still need precise current regulation - so would still love any input anyone could give me.

[mackrackit]

An IGBT might be better for this than a FET.

The current could be detected with a current transducer of some sort with the output from there going to the PIC ADC.

Just thoughts.