Polarity identification and quality testing of 3

If it is an NPN transistor, simply swap the meter rod for measurement, that is, use the black meter rod to touch the pin to be tested that is pinched by hand. In the two tests, the pin corresponding to the red meter rod with the lower resistance is the emitter. (3) The test threshold for thermal stability and amplification capability represents the current amplification factor of the transistor. The larger the maximum value, the better the amplification performance of the transistor. Penetration current represents the thermal stability and noise of a transistor. The smaller the penetration current, transistor the better the thermal stability of the transistor. The more stable the penetration current, the smaller the noise of the transistor. ① Testing of penetration current. To determine the magnitude of the penetrating current, two resistance values are commonly measured: first, test the reverse resistance of the collector junction, and then test the resistance between the emitter and collector. First, contact the red gauge rod with the collector C and the black gauge rod with the base B, as shown in Figure 5-78 (a). At this point, the resistance value should be above 200 ka,transistor  and the larger the value, the better; If the resistance value is very small, it indicates that the reverse saturation current is too large, while the penetration current is larger and should not be used;transistor  If the resistance value is close to zero, it indicates that the collector junction has been broken down. The red gauge rod still contacts the collector electrode C, and then the black gauge rod contacts the emitter electrode E, as shown in Figure 5-78 (b). At this point, the higher the resistance value, the better. If it remains stable above 50 kn, it indicates that the penetration current is small and stable, which means that the thermal stability of the transistor is good and the noise is low.transistor