Forward direction is jointed the switching circuit 1st

摘要

The invention provides a simple and stable infrared light emitting diode (LED) drive circuit for preventing an LED from emitting a continuous intense infrared light when a fault occurs. The driver circuit comprises a voltage source 2, a first transistor 5 connected in series with an LED 4, a second transistor 7 connected in parallel with the LED and a set of operation keys 8 for generating pulse signals. During normal operation when any of the operation keys are pressed a pulse is applied to the base of the series transmitter resulting in current flowing to the LED. If the emitter and collector of the series transistor are short circuited however, the parallel transistor becomes active to prevent current flowing to the LED when operation keys are not pressed. Application is to a remote control transmitter or other communication appliance such as an electronic notebook or personal digital assistant.