Diode and transistor test
- 1. Diode and Transistor Test M Afnan Habibi
- 2. Diode • Being able to determine the polarity (cathode versus anode) and basic functionality of a diode is a very important skill for the electronics hobbyist or technician to have. • Since we know that a diode is essentially nothing more than a one-way valve for electricity, it makes sense we should be able to verify its one-way nature using a DC (battery- powered) ohmmeter as in Figure 1. • Connected one way across the diode, the meter should show a very low resistance at (a). Connected the other way across the diode, it should show a very high resistance at (b) (“OL” on some digital meter models).
- 3. Fig 1. Diode’s one-way nature verification using a DC (battery-powered) ohmmeter
- 4. Transistor • Bipolar junction transistor has three terminals: • Emitter (E) • Base (B) • Collector(C) • The schematic symbol of the BJT is given below:
- 5. Steps to Identify The NPN Type Transistor • Keep the Multimeter in the Diode mode. • Keep the positive probe to the center pin (Base) of the transistor. • Touch the negative probe to the pin-1 (Emitter). You will see some voltage in the multimeter. • Similarly touch the negative probe to the pin-3 (collector) with respect to the pin-2. You will see some voltage in the multimeter. • It will ensure that it is a NPN transistor. The logic behind this is, in NPN transistor • Emitter (E) - N type material - Equivalent to cathode of the diode • Base (B) - P type material - Equivalent to anode of the diode • Collector(C) - N type material - Equivalent to cathode of the diode • If the multimeter positive probe is connected to anode and negative probe is connected to cathode, then it will show voltage. If the connections are interchanged it will not show any value.
- 6. Steps to Identify The PNP Type Transistor • Keep the Multimeter in the Diode mode. • Keep the positive probe to the pin-1 (Emitter) of the transistor. • Touch the negative probe to the center pin (Base). You will see some voltage in the multimeter. • Similarly touch the negative probe to the center pin (Base) with respect to the pin-3 (collector). You will see some voltage in the multimeter. • It will ensure that it is a PNP transistor. The logic behind this is, in PNP transistor • Emitter (E) - P type material - Equivalent to anode of the diode • Base (B) - N type material - Equivalent to cathode of the diode • Collector(C) - P type material - Equivalent to anode of the diode • If the multimeter positive probe is connected to anode and negative probe is connected to cathode, then it will show voltage. If the connections are interchanged it will not show any value.