Analysis of the Function and Principle of Continuous Current Diode

The "freewheeling diode" we usually refer to is named after its role in freewheeling in circuits. Fast recovery diodes or Schottky diodes are generally selected as "freewheeling diodes". It is generally used in circuits to protect components from being broken down or burned out by induced voltage. It is connected in parallel to the two ends of the component that generates induced electromotive force and forms a circuit with it, so that the high electromotive force generated by it is consumed in the circuit as freewheeling current, thereby protecting the components in the circuit from damage.

Continuous current diodes are connected in parallel at both ends of a coil, and when a current flows through the coil, an induced electromotive force is generated at both ends. When the current disappears, its induced electromotive force will generate reverse voltage on the components in the circuit. When the reverse voltage is higher than the reverse breakdown voltage of the component, it can cause damage to components such as transistors and thyristors. The freewheeling diode is connected in parallel at both ends of the line. When the current flowing through the coil disappears, the induced electromotive force generated by the coil is dissipated through the circuit composed of the diode and the coil. This protects the safety of other components in the circuit. A freewheeling diode is connected in reverse parallel at both ends of a relay or inductor in a circuit. When the inductor is powered off, the electromotive force at both ends does not immediately disappear. At this time, the residual electromotive force is released through a diode, and the diode that performs this function is called a freewheeling diode. In fact, it is still a diode, but it serves as a freewheeling function here. For example, why is it necessary to reverse connect a diode between the two ends of a relay coil or a unidirectional thyristor?

Because the coil of a relay is a large inductor that can store electrical energy in the form of a magnetic field, it stores a large amount of magnetic field when it is pulled in. When the transistor controlling the relay changes from conduction to cutoff, the coil loses power. However, if there is a magnetic field in the coil, a reverse electromotive force voltage of up to 1000V will be generated, which can easily break down and push the transistor or other circuit components. This is because the diode is connected in the same direction as the reverse electromotive force, and the reverse electromotive force is neutralized in the form of current through a freewheeling diode, thus protecting other circuit components. Therefore, it is generally a diode with a relatively fast switching speed, like a thyristor circuit, which is used as a contact switch. If controlling a large inductive load, it will also generate high voltage. The principle of back electromotive force is the same as that of a relay. It is also used on the coil commonly used in demagnetization relays on displays.

Often used together with energy storage components to prevent sudden voltage and current changes and provide a pathway. Inductance can provide continuous current to the load through it to prevent sudden changes in load current and smooth the current! In a switching power supply, a freewheeling circuit consisting of diodes and resistors connected in series can be seen. This circuit is connected in parallel with the primary side of the transformer. When the switch diode is turned off, the freewheeling circuit can release the energy stored in the transformer coil, preventing the induced voltage from being too high and causing breakdown of the switch diode. Generally, choosing a fast recovery diode or Schottky diode is sufficient to reduce the reverse potential generated by the coil. It can be seen that the "freewheeling diode" is not a substantial component, but only plays a role in the circuit called "freewheeling".