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![](/i/favi32.png) Power electronics digital notes b. Tech III yearpower electronics digital notesSnubber circuit
Due to overheating, over voltage, over current or excessive change in voltage or current switching devices
and circuit components may fail. From over current they can be protected by placing fuses at suitable
locations. Heat sinks and fans can be used to take the excess heat away from switching devices and other
components. Snubber circuits are needed to limit the rate of change in voltage or current (
di/dt
or
dv/dt
)
and over voltage during turn-on and turn-off. These are placed across the semiconductor devices for
protection as well as to improve the performance. Static
dv/dt
is a measure of the ability of a thyristor to
retain a blocking state under the influence of a voltage transient. These are also used across the relays and
switches to prevent arcing.
Necessity of Using the Snubber Circuit
These are placed across the various switching devices like transistors, thyristors, etc. Switching from ON
to OFF state results the impedance of the device suddenly changes to the high value. But this allows a
small current to flow through the switch. This induces a large voltage across the device. If this current
reduced at faster rate more is the induced voltage across the device and also if the switch is not capable of
withstanding this voltage the switch becomes burn out. So auxiliary path is needed to prevent this high
induced voltage
Similarly when the transition is from OFF to ON state, due to uneven distribution of the current through
the area of the switch overheating will takes place and eventually it will be burned. Here also snubber is
necessary to reduce the current at starting by making an alternate path.
Snubbers in switching mode provides one or more of the following functions
Shape the load line of a bipolar switching transistor to keep it in its safe operating area.
Reducing the voltages and currents during turn-ON and turn-OFF transient conditions.
Removes energy from a switching transistor and dissipate the energy in a resistor to reduce junction
temperature.
Limiting the rate of change of voltage and currents during the transients.
Reduce ringing to limit the peak voltage on a switching transistor and lowering their frequency.
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