Patent ID: 8922238

Claim:
A test circuit for testing a bipolar junction transistor (BJT), the test circuit comprising: a first test circuit comprising a first light-emitting diode (LED) and a first resistor, wherein an anode of the first LED is connected to a power supply, a cathode of the first LED is connected to a collector of the BJT through the first resistor, an emitter of the BJT is grounded; a base of the BJT is connected to the power supply; and the first LED is turned on or off to indicate a type of the BJT; and a protection circuit used to protect the BJT from being damaged due to an over-voltage, wherein the protection circuit comprises an optical coupler (OC), a first transistor, and a second transistor, the OC comprises a second LED, and a phototransistor, an anode of the second LED is connected to the power supply, a cathode of the second LED is connected to the collector of the BJT via a fourth resistor, a collector of the phototransistor is connected to the power supply by a fifth resistor, an emitter of the phototransistor is connected to a base of the first transistor, an emitter of the first transistor is grounded, a collector of the first transistor is connected between an end of a sixth resistor and a base of the second transistor, the other end of the sixth resistor is connected to the power supply, an emitter of the second transistor is grounded, a collector of the second transistor is connected to the power supply through a seventh resistor.