High School Electronic Technology - Transistor Multimeter Polarity Measurement (Pointer Multimeter and Digital Multimeter)

Since the pins of the transistors are not unified, a multimeter is needed for testing.

1. Pointer multimeter

1.1 Determine the base and transistor type (NPN or PNP)

Here’s how to do it:

First, set the multimeter ohmmeter to "R x 100" or "R x 1K".

First assume that one leg of the transistor is the "base" and connect the black test lead to the assumed base b.

Connect the red test lead to the other two poles in turn and measure the resistance.

The judgment is as follows:

If the resistance values ​​measured twice are very small (about a few hundred to a few thousand ohms), the assumed base is correct and the transistor type is NPN.

If the resistance values ​​measured twice are both very large (approximately several thousand to tens of kilo-ohms), the assumed base is correct and the transistor type is PNP.

If the two measured resistance values ​​are one larger and one smaller, the assumed base is wrong, and you should reselect the base for measurement.

1.2 Determine the collector and emitter

The base and type of the transistor have been known through the above operations. The remaining two legs are the collector and emitter. The method of judging the two is as follows:

First, set the multimeter ohmmeter to "R x 100" or "R x 1K".

Connect the black test lead to the assumed collector c and the red test lead to the assumed emitter e, and pinch the collector c and base b with your hands (through the human body, it is equivalent to connecting a bias resistor between bc, and the base b is connected to a high level), and read the resistance value.

Reverse the test leads and retest.

The judgment is as follows:

If the transistor is of NPN type and the first measured resistance is smaller than the second, the assumed collector c and emitter e are correct (the small resistance between c and e indicates that the transistor is turned on and the current passing through the transistor is large); otherwise, the polarities of the two pins are opposite.

If the transistor is a PNP type and the first measured resistance is larger than the second, the assumed collector c and emitter e are correct (the small resistance between c and e indicates that the transistor is turned on and the current passing through the transistor is large); otherwise, the polarities of the two pins are opposite.

1.3 Measuring the β beta β value of a transistor

The method is as follows: hFE is the abbreviation of the DC amplification factor of the transistor.

First turn the switch to the transistor adjustment ADJ position

Short-circuit the red and black test leads and adjust the ohm potentiometer so that the pointer is aligned with the 300hFE scale, which is full deviation.

Then turn the switch to the hFE position and insert the transistor legs to be measured into the ebc sockets of the transistor test socket. The value indicated by the pointer deflection is approximately the DC magnification value of the transistor. (N-type transistors should be placed in the tube holes of N-type transistors, and P-type transistors should be inserted into the tube holes of P-type transistors)

2. Digital multimeter

2.1 Determine the base and transistor type (NPN or PNP)

Here’s how to do it:

First, adjust the multimeter to the diode mode (buzzer mode)

First assume that one of the pins of the transistor is the base, touch the red test lead to that pin, and touch the black test lead to the other two pins respectively, and read the indication.

Then change the black test lead to touch that pin, and the red test lead to touch the other two pins respectively, and read the indication.

The judgment is as follows:

2.2 Determine the collector, emitter and β betaβ values

Here’s how to do it:

First set the gear position to "hFE", you can see a row of small jacks next to the gear position, which are divided into the measurement of PNP and NPN tubes.

The tube type has been determined before. Insert the base into the "b" hole of the corresponding tube type, and insert the other two pins into the "c" and "e" holes respectively. At this time, you can read the value, that is, the β betaβ value.

Then fix the base, swap the other two pins, and read the indication.

Compare the two readings. The pin with the larger reading corresponds to "c" and "e".