Measuring Voltages in a Transistor (INS038E)

To measure voltages at the terminals of a transistor connected to a circuit, we need only a multimeter. With this test we can check the state of the junctions and eventually determine if any polarizing or coupling component of the transistorized stage presents problems.

We recommend an analog multimeter of at least 10 kohm /V or digital for measurements on RF transistors, low power and of power.



The figure shows how to use the multimeter in the indicated tests.






For a silicon NPN transistor we have the following possible measures:

a) Emitter voltage between 0 V and some Volts

b) Base voltage - approximately 0.6 V above the measured voltage at the emitter. For germanium transistors approximately above 0.2 V.

c) Collector voltage - greater than the base voltage up to the value of the supply voltage if the collector charge is of low impedance.



a) Base voltage equals to the emitter - short transistor

b) Zero Voltage - Transistor Open or Short

c) Collector voltage nil or equals to the emitter - short transistor

d) Collector voltage equals to the supply with load that is not of very low resistance - open transistor.