# Designing a fast LED-driver from scratch

I plan to build a LED driver that can pulse a high-power LED (3W) down to the 100s of nanoseconds pulse regime, yet also allows longer pulses (up to 100ms) should be possible. The LED should be driven off a TTL/GPIO signal.

I’m admittedly a bloody beginner in electronics but did some reading upfront. I came to the following conclusions so far, which also might be wrong:

• buck/boost driver are too slow
• timer or avalanche circuits have fixed pulse width
• single mosfet driver can introduce oscillations
• my best bet is a push-pull mosfet driver
• shunt drivers might also be an option

Sadly, I haven’t found a comprehensive tutorial on designing such a driver specifically for driving high-power LEDs. If there is one I have overlooked I would be happy if someone could push me in the right direction. If there really is none, I have the following questions:

1. Which transistor pair would be good to drive a 3W LED in push-pull?
2. How do I calculate the resistors specifically for the LED (3.5V, 700mA)?
3. What type of power supply can I use to drive the circuit? Are voltage regulators interfering in such circuits?

Independently from this: what do I need to do to step such a circuit up to drive a 30W LED?

Thank you!

• It's not possible to pulse <1us with power LED's due to high capacitance. not even close. But you modulate a Laser after it activates. Consider the ESR*Cjcn =T value. 1A white LEDs need a good heatsink but Vf ~ 2.8V+If*0.5Ohm +/-50% – Tony Stewart Sunnyskyguy EE75 Dec 5 '16 at 23:48
• @TonyStewart.EEsince'75 - White LEDs are not suitable for microsecond pulsing due to phosphor persistance. – WhatRoughBeast Dec 5 '16 at 23:57
• that's right about 8ms decay time – Tony Stewart Sunnyskyguy EE75 Dec 6 '16 at 0:03
• Start with a buck circuit with hysteretic control, do not use output capacitor, use a shorting/shunting switch across the LEDs. That can comfortably produce a regulated current pulse of a few hundred ns. In particular, look at the datasheet of LM3409, there are examples and waveforms showing the fast current switching. – rioraxe Dec 7 '16 at 6:20
• What is your app? High-speed photography? – user1890202 Feb 18 '17 at 9:52