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Terminating an LED for fast pulses

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pastro

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Hi All,

I'm using a DG535 to pulse an LED with 10ns pulses ~4V tall in order to test a photomultiplier tube. However, the problem is that the reflections re-trigger the LED in an unwanted way. I need to terminate the LED, but I'm not sure how to get the best combination of maximum LED brightness and minimum reflections. I'm using 50 ohm cable.

Does anyone have experience with this, and if so, would you please suggest a circuit to do this?

Thanks!
 

What you need is a fast LED driver. 10 ns means 100 MHz, so you need a RF power amplifier.
You do not offer any details of the LED you use. IR LEDs typically require 2..3 V and the current is important to know for a specific LED.
A small LED lights with 10-20 mA, high-power LEDs need one amp.

Depending on duty cycle, you may overdrive your LED with 10-ns pulses so it can cool down.
I would try to make a fast driver using a RF power transistor; its e-b input is close to 50 Ohms, and pulse of 0.5 V can open the collector circuit to a desired current.

Be ready to kill some LEDs before you find the best adjustment.
 
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