Notes on the correct voltage loading method for transistors
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Notes on the correct voltage loading method for transistors

Posted Date: 2024-02-07

It can be considered that there are two sets of PN junctions in the transistor. In order for electrons or holes (they are charge carriers, so they are also called carriers) to move and generate current, their voltage must be supplied by a DC power supply.

The correct voltage loading method based on the working principle of the transistor must comply with the following matters.

1. Apply forward voltage between emitter and base

Any ground circuit in the figure satisfies this condition. However, the magnitude of this voltage cannot exceed 1V.

2. Add reverse voltage to collector

The transistor in the picture is NPN type, that is, the collector uses an N-type semiconductor. A reverse voltage is applied to the collector, that is, the collector terminal must be connected to the positive terminal. Otherwise, electrons cannot be guided from the collector terminal across the base region (to flow current through the collector circuit). If the transistor is of PNP type, the collector is a P-type semiconductor and the collector terminal must be connected to the negative electrode.

3. To obtain output, a load resistor must be added

The transistor has an amplification effect, but even if the collector current is obtained, there is no output without the load resistor.

Now that we know its working conditions, how can we judge the base and tube type of the transistor?

Judgment pipe

Select the R*100 (or R*1K) ohm setting, first connect the red test lead to one pin, and the black test lead to the other pin. You can measure the two resistance values, and then use the red test lead to connect the other pin. , repeat the above steps, and measure another set of resistance values. Measure this 3 times. There is a set of two resistance values ​​​​that are both very small. The red test lead corresponding to this set of measured values ​​​​is connected to the base, and the tube is PNP type. On the contrary, if you use a black test lead to connect a pin, repeat the above method. If both measured resistance values ​​are small, the corresponding black test lead is the base, and the tube is NPN type.

discriminating collector

Because the β is large when the emitter and collector of the transistor are correctly connected (the hands of the watch swing greatly), and the β is much smaller when the transistor emitter and collector are connected in reverse. Therefore, first assume a collector and connect it with the ohmic gear (for NPN type tubes, connect the emitter to the black test lead and the collector to the red test lead). When measuring, hold the base and the hypothetical collector with your hands, and the two poles should not be in contact. If the pointer swings greatly, but the pointer swings small after the two poles are reversed, it means that the hypothesis is correct, and the collector and emitter can be determined.

Review Editor: Huang Fei


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