How to use a multimeter to test the performance of common transistors

The method of detecting high-power Darlington tubes is basically the same as that of detecting ordinary Darlington tubes. However, since high-power Darlington tubes are equipped with protection and leakage current discharge components such as V3, R1, and R2, the impact of these components on the measured data should be distinguished in the detection quantity to avoid misjudgment. Specifically, the following steps can be followed:
① Use the multimeter R×10k block to measure the PN junction resistance between B and C, and it should be clearly measured that it has unidirectional conductivity. There should be a large difference between the forward and reverse resistance values.
② There are two PN junctions between B-E of the high-power Darlington tube, and resistors R1 and R2 are connected. When using the multimeter resistance block for detection, when measuring in the forward direction, the measured resistance value is the result of the forward resistance of the B-E junction in parallel with the resistance values ​​of R1 and R2; when measuring in the reverse direction, the emitter junction is cut off, and the measured resistance is the sum of (R1+R2), which is about several hundred ohms, and the resistance value is fixed and does not change with the change of the resistance block position. However, it should be noted that some high-power Darlington tubes also have diodes on R1 and R2. In this case, the measured resistance is not the sum of (R1+R2), but the parallel resistance of (R1+R2) and the sum of the forward resistances of the two diodes.
Detection of high-power transistors
The various methods of using a multimeter to detect the polarity, tube type and performance of medium and low-power transistors are basically applicable to the detection of high-power transistors. However, since the working current of high-power transistors is relatively large, the area of ​​their PN junctions is also large. The larger the PN junction, the greater its reverse saturation current. Therefore, if the multimeter's R×1k block is used to measure the inter-electrode resistance of low-power transistors in medium and motor test instruments, the measured resistance value must be very small, as if the inter-electrode short circuit occurs, so the R×10 or R×1 block is usually used to detect high-power transistors.
Detection of damped output transistors
Set the multimeter to R×1, and measure the resistance between the electrodes of the damped output transistors to determine whether they are normal. The specific test principles, methods and steps are as follows:
① Connect the red test lead to E and the black test lead to B. This is equivalent to measuring the resistance of the equivalent diode of the B-E junction of the high-power tube and the protection resistor R in parallel. Since the forward resistance of the equivalent diode is small, and the resistance of the protection resistor R is generally only 20Ω~50Ω, the resistance of the two in parallel is also small; conversely, swap the test leads, that is, connect the red test lead to B and the black test lead to E, then the measured value is the parallel resistance of the reverse resistance of the equivalent diode of the B-E junction of the high-power tube and the protection resistor R. Since the reverse resistance of the equivalent diode is large, the resistance measured at this time is the value of the protection resistor R, which is still small.
② Connect the red test lead to C and the black test lead to B. This is equivalent to measuring the forward resistance of the B-C junction equivalent diode of the high-power tube in the tube. The resistance value measured is generally small. Swap the red and black test leads, that is, connect the red test lead to B and the black test lead to C. This is equivalent to measuring the reverse resistance of the B-C junction equivalent diode of the high-power tube in the tube. The measured resistance value is usually infinite.
③ Connect the red test lead to E and the black test lead to C. This is equivalent to measuring the reverse resistance of the damping diode in the tube. The measured resistance value is generally large, about 300Ω~∞; swap the red and black test leads, that is, connect the red test lead to C and the black test lead to E. This is equivalent to measuring the forward resistance of the damping diode in the tube. The measured resistance value is generally small, about a few Ω to tens of Ω.
Detection of ordinary Darlington tubes
The detection of ordinary Darlington tubes with a multimeter includes identifying electrodes, distinguishing PNP and NPN types, and estimating amplification capabilities. Because there are multiple emitter junctions between the E and B poles of the Darlington tube, the multimeter should be used for measurement using the R×10k range that can provide a higher voltage.