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Question:

Why the relay discharge diode to reverse

When the coil is energized, the following is +, the above is - But the coil loss of power, the polarity will change? , If not the case, then the diode will not turn ah?

Answer:

The internal coil of the relay is actually an inductor. After power is applied, when the relay is released, the sudden power loss of the coil will produce a higher induced voltage in the opposite direction. This voltage is liable to cause damage to the triode of the driving relay. Therefore, the diodes Parallel to the coil from the offset, discharge current role. DC relay to parallel diodes, This is to prevent the DC relay when the rebounding generated by the circuit on the impact or damage to components, reverse parallel diode for the back to the potential of a circuit. This diode is called a freewheeling diode or called an absorption diode.
May 9, 2017
The internal coil of the relay is actually an inductor. After power is applied, when the relay is released, the sudden power loss of the coil will produce a higher induced voltage in the opposite direction. This voltage is liable to cause damage to the triode of the driving relay. Therefore, the diodes Parallel to the coil from the offset, discharge current role.
May 9, 2017
In general, when we connect the circuit, the relay coil and switch are connected separately (ie, connected to different branches). We can simply use a transistor to control the coil conduction (of course, the other can). When the coil is energized, the relay switch is closed and the circuit is in operation. When the coil is de-energized, the switch disconnect circuit does not work. But this time there is a problem, the coil can store energy (the coil will prevent the current mutation, that is, upstairs to mention the electromagnetic induction, that is, the current can only slowly increase and decrease), if then let the coil power, It will produce a large voltage at both ends, so that it may damage the coil, connected components breakdown. At this time, as long as we connect the diode at both ends of the coil, it can make it produce a loop (power equivalent to the end of the coil at both ends of the short line), so that the energy stored in the coil finished. This diode acts as a freewheel here, and we usually call it a freewheeling diode. (Attached: the voltage at both ends of the capacitor can not be sudden changes in the current at both ends of the inductor)
May 9, 2017

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