Operation of diodes

1. The component

1 la diode

The diode is an electronic component found in mobile electrical installations. The diode is a polarized dipole. That is to say that the component has 2 connections with a connect direction.

The diode allows the current to flow in one direction and opposes its passage in the opposite direction. This is the "no way" of electronics. If we make the analogy with hydraulics, the diode works like a check valve.

2. Symbolization

2 la diode

The diode has 2 legs. The anode (terminal +) and the cathode (terminal -). The symbol makes it possible to represent the direction of current flow.

  • Anode: Letter A

  • Cathode: Letter K

The triangle indicates the direction of current flow while the bar blocks it.

On the component, the gray ring represents the opposition of current flow.

We always use the conventional current direction which goes from (+) to (-).

3. Operation

3 la diode

For the diode to be conductive, it is necessary to apply a threshold voltage to it between the anode and the cathode of approximately 0.6 volts.

In the opposite direction, the diode opposes the flow of current. If the voltage exceeds a certain value ( breakdown voltage ), the diode deteriorates and becomes out of order.

Hydraulic and electrical training

On site in business and/or videoconference

We move with a simulation bench, the training sessions alternate theory and practice.

The simulation bench makes it possible to reproduce industrial and mobile assemblies.

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4. Choice

      The diode is characterized by:

  • Its threshold voltage.
  • Its breakdown voltage.
  • Her intensity running through her.

5. Some Uses

4 la diode

We find the diode installed in parallel with the relays. It is called a free-wheeling diode and is used to protect the relay supply contacts from electric arcs caused by the self-induction effect. (Fig.D)

5 la diode

We find the diode in the electrical circuits in order to supply a consumer by 2 sources of energy (hazard warning light for example). (Fig.E)

6 la diode

The diode is found in the alternators. A diode bridge makes it possible to rectify the alternating current into direct current. (Fig.F)

6. Testing

The diode is defective when it is shorted. It no longer blocks current from the opposite direction.

The diode is defective when it is cut. The current can no longer flow in either direction.

7 la diode

The diode is tested component disconnected from the circuit. With a calibrated multimeter on a diode tester. It is enough to supply the diode by the tester and to note that the diode is conducting on one side and non-conducting on the other. (Fig.G)

In the forward direction, the multimeter indicates the threshold voltage between 0.5 and 0.8 volts depending on the type of diodes used.

In the blocking direction, the multimeter indicates the value "OL" (Over Limit).


Note  : The diode tester provides an internal voltage between 2.5V and 3.5V. It is necessary to have a battery in good working order in order to carry out the test correctly.


7. LED or DEL

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The characteristics of the light-emitting diode are identical to a conventional diode. The notable difference is the light radiation it emits when an electric current passes through it.

The diode must be coupled to a resistor to limit the intensity of the current which crosses it.


8. Zener diode

9 la diode

The Zener diode behaves like a conventional diode, a threshold voltage is necessary for it to be on. In the opposite direction, when the voltage reaches the breakdown value (14 V for example), it becomes conductive but is not destroyed unlike a conventional diode. (Fig.I)


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