High energy pulse output

Want to switch the output of a photoflash capacitor (100 uf, 300 v) into a 10 ohm resistive load. Very low duty cycle <1% using isolated FET or other device with a TTL signal. Thinking FET output optoisolator. Looking for part suggestions.

Hello brahrens, Welcome to the TechForum!

I took a look at our optoisolators with FET outputs and came up with the options in the link below, take a look and see if any are good for you.

Thanks again for choosing Digi-Key!

Hi Nate,

My nominal output voltage is 300 V. Switching the output from a 100 uf capacitor charged to 300 V. These all have a max output voltage of 30 v or less. Am I reading the specs right?


Hi brahrens,

No, I think you’re reading that right. I think what you need is either and isolated gate driver or possibly a photovoltaic isolator to drive a discrete FET of appropriate size.

An isolated gate driver can switch at much higher frequencies than a photovoltaic isolator, but it typically requires a power supply of 15-20V on the isolated FET side of the circuit to drive the gate of the FET. This can come from an isolated DC-DC converter.

If you don’t need to switch fast (faster than a millisecond or so), the photovoltaic isolators can be effective. They generate their own isolated voltage kind of like a tiny solar cell internally. If you go this route, make sure the FET you select can be fully enhanced with a gate voltage of about 5V, as they are typically not guaranteed to produce much more than that.


I’ve come to the same conclusion. I’m looking at an isolator that will take the TTL input and then drive an N-channel power MOSFET. I’ve found a simple circuit using a zener and a gate drain resistor that makes sure the FET comes on hard when you want and it only adds a couple of components. I appreciate your comment, though. It confirms what I was thinking.