Circuit for producing 10ns pulses of several amps

Mr.CRC · 2012-07-20T17:52:32+00:00

Hi:I have been using MOSFET drivers to pulse LEDs at currents of up to 21A(for 100s of ns to several microsecond pulses) and down to about 22nsfor 1A pulses into 1mm^2 power LEDs.I can't get any faster with the drivers I've tried than about 20ns for"parity" optical output power with the 1.0A CW max current typical ofblue 1mm^2 LEDs. (see note 1 below)I wish to achieve 10-20ns pulses of 1-10 amps.Three circuits that come to mind are:1. Capacitive discharge by MOSFET switch such as the Directed EnergyPCO-7110 driver.This circuit has the drawback of a slow trailing edge.2. Discontinuous current mode flyback circuit. The stored current inthe inductor is switched into the LED when the MOSFET turns off.This circuit also has a slower tail than a symmetric drive, but isbetter than RC. I have gotten 30ns or so 3-4A pulses in a LTspice sim,with 100-1000pF in parallel with diode loads.3. Continuous current mode flyback circuit. The stored current in theinductor is switched into the LED when the MOSFET turns off, thenshunted back through the FET when it turns back on.This circuit produces a nice sharp pulse. I have gotten 15ns or so 3-4Apulses in a LTspice sim, with 100-1000pF in parallel with diode loads.At this point I have no idea if the simulated performance can berealized with a physical circuit.Also, much of the challenge is in the MOSFET gate drive. Hence, I keepcoming back to the fact that if the gate driver is fast enough, justhook the LED to it and be done!I did buy some Directed Energy (IXYS) laser diode driver assemblies totest, but haven't gotten to spend much time with them. I still want tobe able to build my own, to meet custom mechanical requirements.Just wondering if there are any completely different approaches to thinkabout?I'm aware of transmission line pulse generation approaches, and wouldconsider them. But that should be a last resort. Those still require afast switch. So it seems all of this boils down to "how to switchon/off several amps in...

Jul 20, 2012 42 Replies

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krw 13 years ago

parallel with the LED. Therefore the current can only flow through the LED for a short while until the all the current available is shunted through the inductor instead.

That's a pretty big inductor. Why would you burn power unnecessarily?

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jc.al.robbins 13 years ago

In case this has not already been cited, I have successfully used the following circuit as the laser driver in a distance measuring application

UHRING W., ZINT C.V., BARTRINGER J., A low-cost high-repetition-rate picosecond laser diode pulse generator, Proc. SPIE 5452, 2004, pp. 583-590, Photonics Europe 2004, Strasbourg (France), April

26-30, 2004, edited by D. Lenstra, G. Morthier, T. Erneux, M. Pessa, ISBN 0-8194-5375-7. Lien

JohnR

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Mr.CRC 13 years ago

Thanks for your reply. I saw it but the idea seemed a bit obscure for my to spend time on. My limitation, not yours.

I'll have a look at your sim below, but it may take me a couple days...

Thanks for the consideration!

_____________________ Mr.CRC crobcBOGUS@REMOVETHISsbcglobal.net SuSE 10.3 Linux 2.6.22.17

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