How to Test the Quality of a Transistor with an Analog Multimeter (Pointer Type)
The pins of the transistor must be correctly identified, otherwise, the connected circuit not only cannot function properly, but may also burn out the transistor. The method for determining the quality of a transistor using a pointer multimeter with known transistor types and electrodes is as follows:
① Testing NPN transistor: Set the multimeter ohm range to "R × 100" or "R × lk", connect the black probe to the base, and then connect the red probe to the other two poles. If the resistance values measured twice are both small, then connect the red probe to the base and the black probe to the other two poles. If the resistance values measured twice are both large, then the transistor is good.
② Testing PNP transistor: Set the multimeter ohm range to "R × 100" or "R × lk", connect the red probe to the base, and then connect the black probe to the other two poles. If the resistance values measured twice are small, then connect the black probe to the base and the red probe to the other two poles. If the resistance values measured twice are large, then the transistor is good.
When the markings on the transistor are unclear, a multimeter can be used to preliminarily determine the quality and type of the transistor (NPN or PNP), and distinguish the three electrodes e, b, and c. The testing method is as follows:
① Using a pointer multimeter to determine the type of base b and transistor: Set the ohm range of the multimeter to "R × 100" or "R × lk", assume that one of the poles of the transistor is the "base", connect the black probe to the assumed base, and then connect the red probe to the other two poles. If the resistance values measured twice are very small (or about several hundred ohms to several thousand ohms), then the assumed base is correct and the tested transistor is an NPN transistor; As above, if the resistance values measured twice are both very large (about several thousand ohms to tens of thousand ohms), then the assumed base is correct and the tested transistor is a PNP type transistor. If the resistance values measured twice are one large and one small, the original assumption of the base electrode is incorrect. In this case, it is necessary to re assume the other electrode as the "base electrode" and repeat the above test.
② Determine the collector c and emitter e: still set the ohm range of the pointer multimeter to "R × 100" or "R × 1k". Taking an NPN transistor as an example, connect the black probe to the assumed collector c and the red probe to the assumed emitter e. Pinch the b and c poles by hand (do not make them directly in contact), connect a bias resistor between b and C through the human body, read the resistance value shown on the meter head, and then connect the two probes in reverse to retest. If the resistance value measured * * times is smaller than * * times, it indicates that the null hypothesis holds, because the resistance values of c and e indicate that the current passing through the multimeter is large and the bias is normal. Nowadays, multimeters with pointers have interfaces for measuring the amplification factor (Hfe) of transistors. Can you estimate the amplification factor of the transistor.
