- Freewheeling diode generally refers in reverse parallel inductance coil , relay , thyristor ends like energy storage element, when the circuit voltage or current mutation, the other elements of the circuit protective diode. Since the freewheeling diode freewheeling functions named in the circuit, typically fast recovery diode or a Schottky diode as a freewheeling diode.
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About freewheeling diode
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Inductance coil, for example, when the current through the coil, an induced electromotive force is generated at both ends there. When the current disappears, the induced electromotive force which have a circuit element generates a reverse voltage. When the reverse voltage is higher than the reverse breakdown voltage element, such as a transistor and other elements will burn. If an antiparallel diode across the coil (sometimes a series resistor), when current flows through the coil disappears, the induced electromotive force generated by the coil will be consumed by the diode circuit and the coils, thus ensuring circuit other security elements in.
For a relay, the relay coil is because a large inductance can store energy in the form of a magnetic field, so when it is attracting a lot of field stores. When the control relay is turned on by the transistor becomes as of the coil will be de-energized, the magnetic field inside the coil but this time did not disappear immediately, the magnetic field generated counter electromotive force, the voltage up to 1000V, it is easy to strike such a high pressure wear or other circuit elements such as transistors. If we antiparallel diode across the relay (relay for, usually a resistor in series with the freewheeling diode to prevent the loop current is too high), because access to the diode and the back electromotive force exactly the same direction, so that the counter electromotive force may be consumed as a current, thereby protecting the other circuit components.
For thyristor circuit, because the SCR is generally used as a contact switch, if the control of a large inductive load, a counter electromotive force will produce the same high pressure, and relays the same principle. Will also be used on the display of freewheeling diode, it is generally used in the degaussing coil relay.
Wheeling diode works
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The figure shows a typical application circuit freewheeling diode, wherein the resistance R optionally decide whether. When the energy storage element is turned VT, positive voltage is negative, the current direction from top to bottom. When VT is turned off, the current in the energy storage element is suddenly interrupted, this time will be induced potential, the direction is trying to keep a constant current, i.e. the current storage element always want to keep from the downward direction. This EMF power source voltage VT across the laminated Jiahou Jia, VT tends to breakdown, can be added for this purpose VD, so the EMF energy storage element can be generated off short circuit, thereby protecting VT.
Freewheeling diode action
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And freewheeling diodes are usually used with the energy storage element, its role is mutated to prevent voltage and current in the circuit, to provide a path for the counter electromotive force power. Inductor through which can provide continuous current to the load, so as not to load the current mutation, smooth current acts! In the switching power supply, able to see a series of a diode and a resistor together freewheeling circuit constituted. This circuit is connected in parallel with the transformer primary.
When the switch is turned off, the freewheeling circuit may relieve the energy stored in the transformer winding, the induced voltage is too high to prevent the breakdown switch.
Selection freewheeling diode
- Usually Schottky diode or fast recovery diodes, such as FR254, FR255, FR256, FR257,1N5204,1N5205,1N5206,1N5207,1N5208,1N5404,1N5405,5406,5407,5408 like.
Notes freewheeling diode
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Freewheeling diode are commonly used in switching power supply, the relay circuit, the thyristor circuit, the IGBT and other circuits, it is widely used. Note that when using the following points:
(1) to prevent freewheeling diode DC coil power, the effective self-inductance means a high voltage potential formed by causing damage to associated components to produce!
(2) of the freewheeling diode polarity can not be wrong, or cause a short circuit accident;
(3) the freewheeling diode reverse voltage is always a DC positive terminal connected to the negative electrode of the direct current, i.e. diode;
(4) works in the freewheeling diode forward conduction state, the state is not the breakdown state or the high speed switch
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