Electric load protection system - has series connected transistor switch inserted in one input lead to guard against polarity error

摘要

The application is primarily to small loads connected to low voltage d.c. supplies where connection of the supply with reversed polarity is possible, and where such a connection could result in damage or malfunction. The line input terminal (UV) of the load (V) is connected to the collector of a transistor (T) whose emitter is connected to the supply terminal (UB). The base connection is joined to the zero volt or opposite polarity supply terminal (O) through a limiting resistor (W). With correct supply connection the transistor saturates and turn on, but with reversed polarity, it remains in the non-conducting state and thus acts as a polarity sensitive switch.