Opto-coupler circuit with switch-on time - has phototransistor operating as constant current source by limitation of capacitance using nonlinear devices

摘要

The optocoupler (OK) includes a light emitting diode (LED) and a photo-transistor (FT) which conduits when light from the diode is received. The photo-transistor is driven as a constant current source (KQ). This is achieved by connection of one output (A1) of the optocoupler to the collector of the phototransistor, and the connection of the other ouptut (A2) of the optocoupler via a resistor (R) to the emitter of the phototransistor, and via a non-linear device (D1-Dn) to the base (B) of the phototransistor. The additional components (R,D1-Dn) may be provided externally to the optocoupler or integrated in the same package. ADVANTAGE - Allows direct adjustment of switching characteristic.