Fast Led Driver With Led And Step Recovery Diode in Series Connection With Current Source Switched by Transistor
Original Publication Date: 1985-Mar-01
Included in the Prior Art Database: 2005-Feb-19
A driver circuit for an LED (light emitting diode) has a tran- sistor with a resistor connected in its emitter circuit and the LED connected between the emitter terminal and collector terminal of the transistor. The resistor forms a current source that supplies current through the emitter-collector circuit of the transistor when the transistor is on and supplies current through the LED when the transistor is turned off. A step recovery diode is connected in the LED branch circuit. When the transistor turns off and the voltage across the LED branch circuit rises, the step recovery diode delays turning on until its voltage has reached a threshold value, and it then turns on rapidly and thereby produces a fast voltage rise across the LED.