Contents
How to choose a fly back diode for a relay?
Here R is the resistance of the fly-back diode in conduction, I is the current flowing through the fly-back diode and L is the inductance supplying the current. If we solve for the power, something very interesting happens…
What should the reverse voltage of a relay be?
In your relay, the coil current is shown as 79.4 mA. Specify a diode for at least 79.4 mA current. In your case, a 1N4001 current rating far exceeds the requirement. The diode reverse voltage rating should be at least the voltage applied to the relay coil. Normally a designer puts in plenty of reserve in the reverse rating.
Can a freewheeling diode be used in a transistor relay?
This will work, but every time you open the switch contacts, an arc will burn for a short time, which shortens the lifetime of your switches. With a transistor output driving a relay, a freewheeling diode is absolutely necessary, because the voltage spike will destroy the transistor.
When to use a diode or a transistor?
With a transistor output driving a relay, a freewheeling diode is absolutely necessary, because the voltage spike will destroy the transistor. When using a switch to turn on/off a relay, omitting the diode will work, but your switch will be happier when you use a diode (one individual diode for each relay).
How is the high voltage spike in a flyback diode determined?
The high voltage spike is determined by the following equation. This means that the faster the current through the inductor is changed, the higher the voltage spike. A Flyback voltage or an Inductive Flyback is a voltage spike created by an inductor when its power supply is removed abruptly.
How is the flyback voltage of a DC power supply determined?
For a 12V DC Power supply, the Flyback voltage spike can be few hundreds of volts. The high voltage spike is determined by the following equation. This means that the faster the current through the inductor is changed, the higher the voltage spike.
What happens when a diode is forward biased?
The resistance of the diode, when it is forward biased, is very less and hence the voltage drop across the diode will be significantly less for the current to flow. This prevents arc at the switching device and as a result protects the switching device from damage.