Snubber Circuit is the one used for suppressing voltage spikes. These are energy absorbing circuits. Normally, the voltage spike occurs due to the inductor present in the circuit. Most basic form of snubber circuit is the RC snubber circuit. Below shows the figure of the snubber circuit having resistor and capacitor in series.
Designing
We take our first assumption as the circuit is having negligible impedance. The value of peak current in the circuit will be calculated using the relation
Where:
Vo= It is the value of Open circuit voltage
Rs =It is the value of Snubber Resistance
The rate of change of voltage w.r.t time is calculated as
From above two equations we can write
According to Ohm’s Law
R=Vo/I
I = switching current
Vo= open circuit voltage
The energy dissipated in the snubber circuit will be equal to the energy dissipated by the capacitor. Because of this the value of the capacitor is selected such that the resistor will dissipate half of the wattage rating of the resistor.
Where:
f= Value of switching frequency
2f= Transitions/ cycle
Condition for snubber circuit
Firstly, the energy stored in the circuit capacitor should be greater than the energy stored in the circuit inductance.
Where:
Vo= open circuit voltage
I = Value of closed circuit current
L= Inductance
Secondly, for this circuit the time constant should be less than 10% of the ON time.
Where:
TON= shortest on-time expected
R = snubber resistance
C = snubber capacitance
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