Testing diodes and transistors with a meter
The meter’s diode range pushes about 1 mA through the part and shows the voltage across it. A good silicon junction reads 0.5–0.7 V one way and OL the other. A transistor is two junctions back to back: base–emitter and base–collector each read like a diode, collector–emitter reads OL both ways.
Open this lesson in the labFree, in your browser, no account needed.
How it works
About 1 mA flows: a 1N4148 shows 0.580 V; a small NPN’s junctions show 0.685 V. Reversed, no current flows and the meter shows OL.
Try it on the bench
- Reverse the meter leads on the diode: OL.
Parts on the bench
- Signal diode
- NPN transistor
- Digital multimeter
In the course
Electronics Technician, module “Components and testing”.