Methods for testing differential pair transistors

Methods for testing differential pair transistors

The differential pair is a semiconductor device that packages two transistors with the same performance into one. It can form a differential amplifier with excellent performance in the simplest way, and is often used in the input and preamplifier of instruments and meters. There are two structural forms of differential pair tubes, one is silicon high-frequency low-power differential pair tubes, typical products include 3CSG3, ECM1A, etc.; the other is silicon low-power differential pair tubes, domestic models include 3DG06A-O6D.

The main contents of using a multimeter to detect differential pair transistors are: (1) identifying electrodes; (2) determining whether they are PNP or NPN; (3) estimating amplification capabilities; and (4) comparing the consistency of the parameters of the two paired transistors. Among them, (1) and (3) are the same as those of ordinary transistors and will not be repeated here. Only (4) is a newly added measurement item.

Note:

(1) When testing differential pair tubes, you should select the multimeter's range. This is because the normal operating voltage of the differential pair tube is relatively high, otherwise the current gain cannot be increased. The battery voltage of the range is too low, and even if the bias resistor is connected, it is not easy for the tube to enter the amplification area, so the value cannot be measured.
(2) Because the test current provided by the range is very small, it can only estimate the amplification capacity of the differential pair tube and make a relative comparison. If the value is calculated according to the formula, it will be much lower than the typical value.
(3) When measuring differential pair tubes, the positions of the two test leads should be swapped.