The reverse diode in electrical circuits serves to protect semiconductor switches, transistors, and powerful power circuits - contactors, from overvoltage. When the contacts are opened, the accumulated magnetic field energy stored in the inductance cannot be stored further as the energy of the electric field of the capacitor, but is converted into a spark or electric arc, which, in the case of contactors, can be applied to their fusion. If the circuit breaks the transistor, then a voltage surge is formed on its terminals - an overvoltage that is significantly larger than the voltage of the power source and can cause a breakdown of the transistor or other semiconductor switch. To protect the transistor, the relay coil or just an inductor must be shunted by a reverse diode. The diode is connected in the opposite direction to the poles of the power source, so in normal mode it does not affect the parameters and operation of the electrical circuit, but creates a path for the current to flow only when the circuit is turned off. As a result, the stored energy of the magnetic field of the coil is dissipated in the form of heat on the active resistance of the coil and diode. Thus, the reverse diode protects the transistor from breakdown caused by overvoltage generated when the electrical circuit is disconnected.