05-07-2012, 02:20 PM
Snubber Circuits
Snubber Circuits.pdf (Size: 75.75 KB / Downloads: 50)
RC Snubber Circuits
RC snubber circuits are normally connected across a switching device to limit the
dt dv
. An RC snubber circuit can be polarized or unpolarized. A forward-polarized RC
snubber circuit shown in Figure 1 is appropriate when a thyristor or a transistor is
connected with an anti-parallel diode. R limits the forward
and R1 limits the
discharge current of the capacitor when Q1 is turned on.
BJT Snubbers
A Bipolar junction transistor (BJT) experiences high stresses at turn-on and turnoff
when both its voltage and current are high simultaneously, thus causing a high
instantaneous power dissipation. Transistors require turn-off, turn-on and overvoltage
snubbers.
Turn-off snubbers
A Turn-off snubber as shown in Figure 5 is used to provide a zero voltage across
the transistor while the current turns off. At turn-off in the presence of this snubber, the
transistor current C
i decreases with a constant
dt
di
and ( ) O C
I − i flows into the capacitor
through the snubber diode DS. Figure 6 shows the voltage rise across the snubber
capacitor CS.
Power MOSFETS
A small RC turn-off snubber as shown in Figure 10 can be used to prevent voltage
spikes and voltage oscillations across a MOSFET during device turn-off. The large peak
current handling capability of the MOSFET and the fact that its switching speed can be
easily controlled by controlling the gate current eliminates the need for a turn-on snubber
in most cases.
Snubber Circuits.pdf (Size: 75.75 KB / Downloads: 50)
RC Snubber Circuits
RC snubber circuits are normally connected across a switching device to limit the
dt dv
. An RC snubber circuit can be polarized or unpolarized. A forward-polarized RC
snubber circuit shown in Figure 1 is appropriate when a thyristor or a transistor is
connected with an anti-parallel diode. R limits the forward
and R1 limits the
discharge current of the capacitor when Q1 is turned on.
BJT Snubbers
A Bipolar junction transistor (BJT) experiences high stresses at turn-on and turnoff
when both its voltage and current are high simultaneously, thus causing a high
instantaneous power dissipation. Transistors require turn-off, turn-on and overvoltage
snubbers.
Turn-off snubbers
A Turn-off snubber as shown in Figure 5 is used to provide a zero voltage across
the transistor while the current turns off. At turn-off in the presence of this snubber, the
transistor current C
i decreases with a constant
dt
di
and ( ) O C
I − i flows into the capacitor
through the snubber diode DS. Figure 6 shows the voltage rise across the snubber
capacitor CS.
Power MOSFETS
A small RC turn-off snubber as shown in Figure 10 can be used to prevent voltage
spikes and voltage oscillations across a MOSFET during device turn-off. The large peak
current handling capability of the MOSFET and the fact that its switching speed can be
easily controlled by controlling the gate current eliminates the need for a turn-on snubber
in most cases.