Snubber
A snubber is a simple electrical circuit used to suppress ("snub") electrical transients. Snubbers are frequently used with an inductive load where the sudden interruption of current flow would lead to a sharp rise in voltage across the device creating the interruption. This sharp rise in voltage might lead to a transient or permanent failure of the controlling device.
| Contents |
RC snubbers
Frequently, a snubber can consist of just a small capacitor in series with a small resistor. This combination can be used to suppress the rapid rise in voltage across a thyristor, preventing the erroneous turn-on of the thyristor; it does this by limiting the rate of rise in voltage (dV/dT) across the thyristor to a value which will not trigger it. Snubbers are also often used to prevent arcing across the contacts of relays (and the subsequent welding/sticking of the contacts that can occur). An appropriately-designed RC snubber can be used with either dc or ac loads.
Diode snubbers
When the current flowing is dc, another often seen form of a snubber is a simple rectifier diode placed in a circuit in parallel with an inductive load (such as a relay coil or electric motor. The diode is installed in the direction that ordinarily wouldn't allow it to conduct. When current to the inductive load is rapidly interrupted, a large voltage spike would be produced in the reverse direction (as the inductor attempts to keep current flowing in the circuit). Placing the snubber diode in inverse parallel with the inductive load allows the current from the inductor to flow through the diode rather than through the switching element and the energy stored in the inductive load is dissipated in the series resistance of the inductor and the (usually much smaller) resistance of the diode (see). One disadvantage of simple rectifier diode used as a snubber is that because the diode allows current to keep flowing, the relay may stay picked-up slightly longer; some circuit designs must account for this delay in the dropping-out of the relay.
More-sophisticated solid-state snubbers
In some dc circuits, a varistor (Transorb) or inverse-series Zener diodes may be used instead of the simple diode. Because these devices dissipate significant power, the relay may drop-out faster than it would with a simple rectifier diode.
In ac circuits, a rectifier diode cannot be used and one of the more complex (and bidirectional) snubber designs may be used instead.