Snubber Resistors In Switching Applications

Snubber circuits are used in a wide range of power applications to prevent damage to switching circuits and sensitive electronic components. In this post, we discuss the role of snubber resistors in power switching applications. We restrict our discussion to passive snubber circuits that dissipate pulse energy in the resistor.

THE NEED FOR SNUBBER CIRCUITS

If the current is interrupted (for example as a switch opens) to an inductive load voltage transients are generated. To avoid damage to the switch, the circuit and sensitive components it is important to suppress (snub) these transients.

The purpose of a snubber circuit is to absorb energy generated by the inductive elements in a circuit on switching. A snubber circuit should reduce losses due to switching and reduce EMI that may damage sensitive electronic components.

Snubber circuits may be designed to clamp a voltage transient at a specified level or control the rate of rise of a voltage pulse. An appropriate snubber circuit should improve the performance and reliability of switching circuits.

Snubbers are often used in combinations to control both the current and the voltage of the switch. Some applications may have two or three snubbers merged into one network.

COMMON POWER SWITCHING APPLICATIONS

One of the most common electronic switches is power converters. These are used in a wide variety of power applications including motor control.

The basic function of a power converter circuit is to deliver an electrical output of a specified voltage, current and frequency. Power converter usually includes a feedback loop from the load to control their output.

RESISTOR SNUBBER CIRCUITS

The most common snubber circuit utilizes a snubber resistor and capacitor connected in series across the switch. The capacitor provides an alternative path for current generated by the inductive load at switch off. It also protects against high voltage and high rate of change of voltage (dv/dt).

The purpose of the snubber resistor is to limit the discharge current of the capacitor. The snubber resistor must have low self inductance which tends to rule out wirewound devices. Thick film snubber resistors are often the best choice as they offer low inductance, high density for a given power rating, excellent power handling capability and relatively low cost.

The components in snubber circuits are subjected to high stresses. A snubber failure can lead to damage to the switch and other circuit components. It is therefore important to select the snubber resistor and capacitor with care.