Testing diodes

Beginners can use multimeter to test the performance of diodes in amateur conditions. Before testing, switch the multimeter to RX1K gear of Ohm gear (pay attention not to use RX1 gear, in order to avoid excessive current burning diodes), and then short circuit the red and black pens to zero ohm.

1. Forward Characteristic Testing

The black pen of the multimeter (positive in the meter) touches the positive of the diode, and the red pen (negative in the meter) touches the negative of the diode. If the needle is stopped in the middle of the dial instead of setting to zero, then the resistance is the forward resistance of the diode. Generally, the smaller the forward resistance, the better. If the forward resistance is zero, it means that the core is damaged by short circuit. If the forward resistance is close to infinite value, it means that the core is broken. Short-circuit and open-circuit pipes can not be used.

2. Reverse Characteristic Testing

If the red pen of a multimeter touches the positive pole of the diode and the black pen touches the negative pole of the diode, the tube will be qualified if the needle points at or near the infinite value.

Application of Diodes

1. Rectifier Diode
By using the single conductivity of the diode, alternating alternating direction AC can be converted into pulsating DC in a single direction.

2. Switching Elements
The resistance of the diode under forward voltage is very small, and it is in the on state, which is equivalent to a switch on. Under reverse voltage, the resistance is very large, and it is in the cut-off state, just like a disconnected switch. Using the switching characteristics of the diode, various logic circuits can be formed.

3. Limiting element
The forward voltage drop of the diode remains unchanged (0.7V for silicon tube and 0.3V for germanium tube). Using this characteristic, as a limiting element in the circuit, the signal amplitude can be limited to a certain range.

4. Relay Diode
It plays a relay current role in inductance neutralization of switching power supply and inductive loads such as relays.