A diode is an electrical device that allows the electric current to flow in one direction only. The most common diodes are semiconductor diodes. However, other types of diodes also exist. A diode by definition is a small signal device (I< 1A). Rectifiers are devices with I>1A.

Diodes are made up of p-type and n-type semiconductors. The lead connected to the p-type semiconductor is the anode and the one attached to the n-type semiconductor is the cathode. Therefore, the n-type end is the negative terminal, and the p-type end is the positive terminal.

If we connect a source of power (battery) in such a way that the positive terminal of the battery is connected to the anode and the negative to the cathode, current will flow through the diode. If we reverse the connections, then current would not flow. Thus, diodes act as a valve through which current can flow in a single direction only.

A diode is schematically represented like this:-


Image from Wikipedia


In this line diagram, the cathode is on the right, and the anode is on the left.

There are a few terms that describe the properties of a diode.

  1. Forward bias allows current to flow through the diodes. Here, the positive side of the power source is connected to the anode and negative is connected to the cathode.


    Image from Wikipedia

  2. Reverse bias does not allow current to pass through a diode. Thus, diodes behave as an insulator (up to an extent).
  3. Peak inverse voltage is the maximum reverse bias a diode can sustain. If the voltage increases beyond the peak inverse voltage, then the diode will break down and allow current to flow in reverse bias as well.
  4. Forward voltage drop is the amount of energy that is lost within a diode. Therefore, a power source must produce a voltage in excess of the forward voltage drop to allow electric current to flow through ?diodes.
  5. Different diodes can allow a different amount of current to flow through them. Thus, each diode has a maximum current rating. If we exceed this value, then the diode will be damaged.

Uses of Diodes

Diodes have many scientific and industrial applications. Diodes are used in radio transmission, power conversion, protection against voltage surges, logic gates, to measure temperature, and to steer the direction of electric current.

Diodes are also used in musical equipment like a keyboard. Electronic musical keyboards use keyboard matrix circuits to reduce the amount of wiring. However, if several keys are pressed simultaneously, current can flow backwards through the channel. This (backflow) can trigger phantom keys and ghost sounds are heard. By soldering diodes to the keyboard matrix, it is possible to eliminate this problem.

Particle detectors that detect ionising radiation also contain diodes.

Finally, are diodes and batteries similar?

A diode is a valve that directs the flow of current. On the other hand, a battery is a power source. Diodes will not conduct electricity unless connected to an energy supply like a battery. Therefore, a diode and a battery are not the same.