LED driver combines high speed, precision


Posted on Sep 17, 2012

The LED driver in Figure 1 illuminates retinal neurons in a biological experiment that has similar requirements. For a given LED at a given current, the intensity is stable, so switching a stable current is a simple and effective way to obtain the needed function. The circuit provides current pulses to the LED with rise and fall times lower than 500 nsec and overshoot lower than 7%. You can make the current computer-programmable by replacing the potentiometer with a DAC. The circuit comprises an adjustable, regulated current source (IC1 and Q2), an overdriven differential amplifier (Q3 and Q4) acting as a switch, and a level shifter (Q1) to shift the TTL input signal to levels needed to drive the differential pair.






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