Question

By using multimeter distinguish between n-p-n and p-n-p transistor.

Hint:

To distinguish between the collector and emitter, one method is to look at the multimeter readings. The forward voltage drop between Base-Emitter (BE) is usually slightly higher than between Base-Collector (BC). However, the most reliable way is to check the transistor's datasheet using the part number printed on it.

Answer 1

Step 1: Understanding the Concept:
A Bipolar Junction Transistor (BJT) consists of three layers of semiconductor material. It can be of two types: NPN or PNP. Internally, a transistor can be thought of as two diodes connected back-to-back. The central region is the Base (B), and the outer regions are the Emitter (E) and Collector (C). We can use a multimeter in diode test mode or resistance mode to identify the base and determine the type.
- NPN: P-type base between two N-type regions. Current flows from Collector to Emitter. - PNP: N-type base between two P-type regions. Current flows from Emitter to Collector.
Step 2: Apparatus Required:
- A digital multimeter with a diode test function or ohmmeter function. - NPN and PNP transistors for testing.
Step 3: Detailed Procedure:
1. Set the Multimeter: Set the multimeter to the diode test mode. In this mode, the multimeter sends a small current through its probes and displays the voltage drop.
2. Identify the Base Terminal: A transistor has three terminals. The base is the terminal that shows a diode-like connection to the other two. - Arbitrarily label the pins 1, 2, and 3. - Place the positive (red) probe on pin 1. Touch the negative (black) probe to pin 2 and then to pin 3. If you get a voltage reading (typically 0.5V to 0.7V) in both cases, then pin 1 is the Base and the transistor is NPN (P-type base). - If you get no reading, move the red probe to pin 2 and repeat. Then move to pin 3 and repeat. - If no combination works, switch the probes. Place the negative (black) probe on pin 1. Touch the positive (red) probe to pin 2 and then to pin 3. If you get a reading in both cases, then pin 1 is the Base and the transistor is PNP (N-type base).
3. Confirm the Type: - NPN Transistor: The base is found when the positive (red) probe is placed on it, and the negative (black) probe gives a reading on the other two pins. (Think: Positive on P-type base). - PNP Transistor: The base is found when the negative (black) probe is placed on it, and the positive (red) probe gives a reading on the other two pins. (Think: Negative on N-type base).
Step 4: Result:
By following this procedure, one can first identify the base terminal of the transistor. Based on the polarity of the multimeter probes that results in two forward-biased readings from the base, the transistor can be distinguished as either NPN or PNP.