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Requirement to determine terminals (base, emitter, and collector) and type (PNP or NPN) transistor using an AVO meter or multimeter or digital multitester, is multitester must have a diode test feature. Diode test feature is usually denoted by symbol of a diode, as shown in multitester's picture below.

multimeter_with_diode_test_feature
We take an example to be measured is transistor type C945, which is quite widely use. We learned to determine terminals and type of transistor C945, and the following steps:

1. Measuring and create tables of measurement
  • Set Multitester the rotary knob of multitester on diode test feature
  • Imagine or describe the position of terminals transistor with sequence numbers 1, 2, and 3
  • Create a table with 6 units of measurement measuring point, ie 1-2, 1-3, 2-3, 2-1, 3-1, and 3-2
  • Specify black probe or negative test probe for the first number, and red probe or positive test probe for the second number, ie the measuring point 1-2, the black probe at point 1, and the red probe at point 2
  • Record the results of each measurements

    measuring_base_transistor_c945


2. Determine terminals and type of transistor
On the measurements table, there are two measurement points that get results, that is point 1-3 at 0.720 VDC, and point 2-3 at 0.716 VDC (see figure above). It is time for us to determine the terminals and type of transistor, by the way:
  • Base is the same number found on the two measuring points
  • Type NPN or type PNP, we can set it to see what probe is connected to the base. If base point connected to black probe, then PNP type transistor, and when base point connected to red probe, then NPN type transistor
  • Emitter-Base forward bias greater than Collector-Base, or EB > CB, that is PNP type transistor. Base-emitter forward bias greater than Base-Collector, or BE > BC, that is NPN type transistor


So we get the conclusion:
  1. At point 3 the transistor base C945
  2. C945 is a NPN transistor, the base on red probe
  3. At point 1 terminal emitter and at point 2 terminal collector C945, because the point 1-3 > 2-3
  4. Terminals and type of transistor C945 as shown in the picture below

    transistor-c945

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3 comments

  1. Pls wat about BC 547 and 2N2222?

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  2. The most basic things we measure are voltage and current. Collector pin will show the continuity with metal case of transistor. Out of remaining two pins, Base and emitter can be identified by setting multimeter in diode mode. For example in case of NPN transistor multimeter in diode mode will show 0.5 to 0.7 V drop if positive pin of multimeter is connected to the base and negative to the emitter pin of the transistor.Thanks.

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  3. Using a portable Fluke device will enable you to measure the values of current at frequent intervals and take necessary action.www.themultimeterguide.com

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