Here you will find our development for a bipolar power transistor tester. It measures the short-circuit forward current ratio (Iout/Iin @Vout=0) commonly known as h21E.
Commonly in everyday practice we need to use two or more bipolar power transistors in parallel, in a push-pull schematic. In order for the transistors to work with identical parameters of currents and gain, as well as to minimize the non-linear distortions, and to reduce heat peaks, they must be with the same h21E parameter.
The unit works like a current generator and measures the base current of bipolar power transistors N or P type. By reading the milliammeter you can quickly compare the h21E values of the measured transistors and to select those with similar parameters for work in a couple or in parallel.
The parameters in the schematic are for a milliammeter with 100 microamperes and internal resistance of 1000 ohms. If you need to use a meter with different values from the above, you need to recalculate R 3,4,5,6,7,8 depending on the new internal resistance. The device and the schematic are easy to implement.