A relay coil suppression diode, also known as a flyback diode, freewheeling diode, or snubber diode, is an electronic component that is commonly used in relay circuits and other applications involving inductive loads. It is used to prevent voltage spikes and other potentially damaging effects that can occur when an inductive load (such as a relay coil) is turned off or de-energized.
When an inductive load is energized, it stores energy in its magnetic field. When the power to the load is suddenly interrupted, as is the case when turning off a relay coil, the magnetic field collapses rapidly. This collapse of the magnetic field induces a voltage spike in the reverse direction across the coil. This voltage spike can lead to arcing, electrical noise, and potential damage to the relay contacts or other components in the circuit.
The relay coil suppression diode is connected in parallel with the relay coil, with its anode connected to the positive supply voltage and its cathode connected to the negative side of the coil (or the common ground). When the relay coil is energized, the diode is reverse-biased and remains non-conductive. However, when the coil is de-energized and the magnetic field collapses, the diode becomes forward-biased and provides a path for the induced current to flow. This effectively creates a loop for the energy stored in the coil's magnetic field to dissipate safely.
In summary, a relay coil suppression diode is used to:
Prevent voltage spikes: By providing a path for the collapsing energy in the inductive load to dissipate, the diode prevents voltage spikes that can damage components in the circuit.
Reduce arcing: The diode reduces the arcing across the relay contacts when the coil is de-energized, prolonging their lifespan.
Minimize electrical noise: The diode helps reduce electromagnetic interference (EMI) and radio frequency interference (RFI) that can be generated by rapid changes in current.
In many applications involving relays, such as automotive electronics, home automation, and industrial control systems, using a relay coil suppression diode is a common practice to ensure reliable and safe operation of the circuit.