![]() The article was first published in June 2006 and has recently been updated. ![]() Table II shows the pin-outs of some common transistors. In various transistors, the pin configurations are different, so it is necessary to go through the datasheets to identify the pins. Construction & testingĪssemble the circuit on a general purpose PCB and enclose it in a small case. The cathode of one LED forms the anode of the other, so depending on the direction of current flow either red or green LED lights up. This is an automatic Transistor Tester, to identify pinout and characteristics of various discrete semiconductors ( Transistors NPN, PNP, MOSFETs, etc ). The tester can also be used as a GO/NO GO tester to match unmarked devices. An audible signal gives an indication of gain. The status of bicolour LED1 for different conditions of the transistor is shown in Table I.īicolour LED1 used in the circuit is a two-lead version with red and green LEDs connected in inverse parallel inside a common case. Transistor Tester for Polarity: This tester checks the transistor for polarity (PNP or NPN). ![]() ![]() This is because output pin 4 of N2 is at low level. This happens due to the high state of outputs at pins 10 and 11 of gates N3 and N4, respectively. If the transistor is pnp type, the current flow is reversed and the red half of bicolour LED1 glows. If the TUT inserted in the socket is npn type, the current flows from output pin 4 of gate N4 through bicolour LED1 and its green half glows.
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