## snubber circuits for power electronics

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## What is snubber?

The snubber is a circuit which snubs or limits the switching voltage amplitude and its rate of rise (dv/dt). Hence it reduces the power dissipation in power electronic switching networks.

• Reduces the voltage and current amplitude.
• It limits the rate of rise of voltage and current
• Reduces the power dissipation in switching networks
• Reduce EMI by damping voltage and current ringing

## snubber circuit for power electronics

The Circuit shows a simple power switching network with a power semiconductor switch and resistive load. When the power semiconductor is switching on or off, the device voltage and current are large, resulting in high power dissipation across the device with high energy loss. The ideal wave forms of switch voltage, current and power is shown in figure during switching operation.

When the switch is open to interrupt the current flow in resistive load, there will be a linear variation of switch voltage and current as shown in the wave form. The resultant peak power dissipation is 1/4 of product of maximum of voltage and maximum current which is very high in high voltage switching circuits. If the load is inductive then the power dissipation is appreciably large, because inductance to prolong current flow.

This turn off losses can be minimized with the snubber capacitor connected across the semiconductor switch as shown in figure. As the switch opens, current is diverted in to the snubber capacitor, which is initially uncharged. The current diversion slows the buildup of switch voltage, and as a result current drops to a low value before the switch voltage has increased significantly. This slow increase in switch voltage produces a substantial reduction in the switching energy loss. With this arrangement of sunnbers and power semiconductor switches we can attain high frequency of operation and low switching losses.

When the switch is closed at the start of its conduction angle, the snubber capacitor discharges through the closed switch. The discharge current is usually limited by placing a small resistor in series with snubber capacitor as shown in figure b. This gives the basic RC snubber circuit with time constant T= RC.