Testing the Operating Status of a Transistor with a Multimeter
For example, if a power amplifier has no output and one of them only measures the voltage between the base and emitter as 0V (measured on the circuit board), does it mean that the transistor is damaged? From the given conditions, it is impossible to determine whether the transistor is faulty based on existing data. Two points need to be noted: the power amplifier output ensures whether the transistor is used as an amplifier or a switch transistor. In addition, if it is used as an amplifier, the bias circuit of the transistor should be checked first (if there is no bias circuit, the base of the transistor should be negative when working normally).
Can a multimeter be used to determine the quality of transistors on a circuit board? What is the voltage at each pole of a transistor during different stages such as amplification, saturation, and cutoff? Obviously, this method can only be used as a reference. It is also necessary to cut off the power and test the online resistance, or even remove the multimeter from the transistor for retesting. As for the voltage at each pole of the transistor, in the amplified state: Uc>Ub>Ue (PNP) or (Ue>Ub>Uc (NPN), in other words, the emitter junction is positively biased and the collector junction is negatively biased. Satisfied states: Launch junction is positively biased; The collector junction is positively biased. Cut off state: launch junction reverse bias; The collector junction is reverse biased. The specific voltage depends on the actual situation, but it must always meet the above conditions.
Let's briefly talk about the measurement method of a multimeter for a transistor. Firstly, without disconnecting the circuit, the voltage range of the multimeter can be used directly to determine which state the transistor is in.
Measure the collector emitter voltage, which is approximately between 0.3 and 0.6 volts, and is in a saturated state.
Measure the collector emitter voltage, which is almost equal to the voltage and is in the cut-off state.
Measure the collector emitter voltage between 1.0v and (power supply voltage-1) v, in various amplification states.
The voltage between the base and emitter is 0, but it cannot be confirmed that the transistor is damaged at this time, and it needs to be analyzed according to the specific situation.
