Light emitting diode control circuit - has emitter-follower, with transistor at input end to prevent excessive increase in collector current for each alternation of control signal

摘要

The control circuit for regulating the light emission from a light emitting diode (LED) uses a binary control signal at the input (SV). The diode is in the collector circuit of a transistor (T) forming the output stage. A resistance (R1) connected to the base of the transmitter is in parallel with a further resistance (R7) and a capacitor (C3). This forms an emitter follower arrangement with a further transistor (T2) towards the input end, which has a resistance (R2) connected between its emitter and the power supply (V2). This arrangement prevents an excessive increase in the collector current (iD) each alternation of the control signal. An additional circuit controls the input signal which can vary in amplitude and length, maintaining a square waveform for the control pulses.