FAST, High Energy Pulser
This circuit is designed to provide very fast, high current
pulses into laser diodes and LEDs. It can be modified to drive
ultrasonic transducers as well. The light pulses from the laser are
typically used for range-finder applications as well as fluorescent
excitation sources. Some blue LED's from Nichia will generate UV
energy when overdriven with short, high-current pulses.
The circuit is designed around a transistor designed for this
application: the DE150 from Directed Energy, Inc (www.directedenergy.com). The circuit works as follows:
the 78S40 forms a basic 15V to 100V flyback DC to DC converter. The
100 volts is then used to charge the four, 1000pf caps connected to
the source pins of Q1. When Q1 is turned on, the caps discharge
through the laser diode dissipating 1/2*C*V^2 of energy. JP1 can be
used as a current monitor. Multiply the observed voltage by four to
determine the current through the diode.
Careful attention to layout will yield the best turn-on times.
Keep the leads short and the traces fat. For more information on
designs of this type, we strongly recommend a visit to the DEI site
referenced above.