Transistor tester
{{Short description|Electrical instrument}}
File:Tektronix 177 Transistor Tester.jpg 177 curve tracer]]
Transistor testers are instruments for testing the electrical behavior of transistors and solid-state diodes.{{cite book|title=Introduction to Electronics: A Practical Approach|author=Earl D. Gates|year=2000|publisher=Thomson Delmar Learning|isbn=0-7668-1698-2}}
Types of tester
There are three types of transistor testers each performing a unique operation.
- Quick-check in-circuit checker
- Service type tester
- Laboratory-standard tester
In addition, curve tracers are reliable indicators of transistor performance.
= Circuit Tester =
A circuit tester is used to check whether a transistor which has previously been performing properly in a circuit is still operational. The transistor's ability to "amplify" is taken as a rough index of its performance. This type of tester indicates to a technician whether the transistor is dead or still operative. The advantage of this tester is that the transistor does not have to be removed from the circuit.
=Service type transistor testers=
These devices usually perform three types of checks:
- Forward-current gain, or beta of transistor.
- Base-to-collector leakage current with emitter open(ico)
- Short circuits from collector to emitter and base.
Some service testers include a go/no-go feature, indicating a pass when a certain hfe is exceeded. These are useful, but fail some functional but low hfe transistors.
Some also provide a means of identifying transistor elements, if these are unknown. The tester has all these features and can check solid-state devices in and out of circuit.
Transistor hfe varies fairly widely with Ic, so measurements with the service type tester give readings that can differ quite a bit from the hfe in the transistor's real life application. Hence these testers are useful, but can't be regarded as giving accurate real-life hfe values.
= Laboratory-standard transistor tester or Analyser =
This type of tester is used for measuring transistor parameters dynamically under various operating conditions. The readings they give are absolute. Among the important characteristics measured are:
- Icbo collector current with emitter open (Common base)
- ac beta (Common emitter)
- Rin (Input resistance)
Transistor testers have the necessary controls and switches for making the proper voltage, current and signal settings. A meter with a calibrated "good" and "bad" scale is on the front.
In addition, these transistor testers are designed to check the solid-state diodes. There are also testers for checking high transistor and rectifiers.
See also
- Load pull, a colloquial term applied to the process of systematically varying the impedance presented to a device under test
References
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{{Electrical and electronic measuring equipment}}