In electronic systems it is important to control voltage transients to prevent damage to electronic components. Snubber circuits manufactured using a power resistor and capacitor are one solution.

In electronic systems voltage spikes are generated by circuit inductance when a switch (mechanical or semiconductor) is opened. These voltage spikes (ringing) can damage electronic components and must be damped or eliminated. A snubber circuit constructed using a power resistor in series with a capacitor connected across the switch is a common solution.

A snubber circuit provides an alternative path for the current flowing through a circuits intrinsic leakage inductance and provides:

• Elminates (or reduces) voltage or current spikes.
• Reduced losses due to switching.
• Reduced electromagnetic interference with other electronic equipment by reducing the ringing component.
• Transfer power dissipation to a power resistor and away from the switch.
• Shapes the load and keeps it within a safe operating area.

A power resistor manufactured using thick film technology is an ideal choice as it can dissipate a large amount of power from a small physical area and it is low inductance. Carbon film resistors may also be used but wirewound resistors are not applicable due to their relatively high inductance.

Snubber circuit design involves compromises including voltage rate, peak voltage, turn off time and component cost. In some cases paper design is not sufficient and experimentation is required to achieve the optimum result. Choosing the perfect power resistor can compromise the capacitor choice and visa versa.

The capacitor size may be maximised to maximise damping but as the capacitor size is increased more power will be dissipated in the power resistor. This is just one example of the trade off required in snubber circuit design. Often key parameters required to calculate the appropriate resistor and capacitor value (such as circuit inductances) are not known and each application presents its own challenges. Design of snubber circuits can therefore be a complex task.

The solution is often to make appropriate assumptions to simplify calculations, choose a power resistor and capacitor value, construct the snubber circuit then observe the result. Modifications may then be made to the circuit until an optimum result is achieved.

Although simple in principle snubber circuits manufactured using a power resistor and capacitor present a number of design challenges. If designed incorrectly the circuit will fail to control voltage transients appropriately which could result in damage to sensitive electronic circuits and system failure. Most capacitor and resistor manufacturers will provide application and design advice to ensure the best possible design is implemented.