how to switch some high power LEDs quickly?

I'm trying to flash some high power LEDs at a constant current off of an external trigger (at a fairly high frequency). I'm trying to use the LT3741 LED driver, but I'm having trouble with the discharge rate above 40 Hz. I'm trying to use the standard application circuit. Any ideas on how to discharge faster?

That driver doesn't have any way of discharging the LEDs. I am guessing that you have the LEDs in series, and the string of LEDs in parallel with the outout capacitors.

Those capacitors will keep the LEDs turned on for ages. You need to reduce them and it's a good idea to fit a discharge circuit.

You are using a switching regulator which is relatively slow to turn off because of the filter caps. For faster switching you can use a transistor at the output. Since the power supply output is a constant current, you would connect the transistor from the power supply output to common. This will shunt the current from the supply to ground to turn off the LEDs (a constant current supply does not like to be open circuited and is not damaged by being shorted to ground). It will require a small power transistor to carry the LED current plus discharge the output cap.

I am not quite clear on what you are doing, are you trying to switch the LT3741 on/off at some frequency (40hz and above) to flash the LEDs?

If so, I think you are using the wrong approach.

Having looked at the datasheet, there is no specification for switching to output on/off.
If you look at the 20A LED driver circuit in the datasheet, there is a 680uF capacitor on the output, there is no way that you are going to charge/discharge this at a fast rate.

I think you need to use the LT3741 to provide the current, and a separate switching circuit such as a transistor or MOSFET to switch the current in the LED.

JimB

Thanks guys. To be clear, what I'm trying to do is use the ctrl 1 pin of the driver to switch between two currents from an external clock as demonstrated in the spec sheet. The capacitors are definitely what are holding up the voltages, so I'll try swapping them out for lower capacitance ones.