MT5F33743
© Fuji Electric Co., Ltd. All rights reserved.
5-6
Fig. 5-8 Schematic waveform for active clamp circuit
3.5 Spike voltage suppression circuit - clamp circuit -
Fig. 5-7 Active clamp circuit
In general, spike voltage generated between
collector to emitter can be suppressed by
means of decreasing the stray inductance or
installing snubber circuit. However, it may be
difficult to decrease the spike voltage under
the hard operating conditions. For this case, it
is effective to install the active clamp circuits,
which is one of the spike voltage suppressing
circuits.
Fig. 5-7 shows the example of active clamp
circuits.
In the circuits, Zenner diode and a diode
connected with the anti-series in the Zenner
diode are added. When the
V
CE
over
breakdown voltage of Zenner diode is applied,
IGBT will be turned-off with the similar voltage
as breakdown voltage of Zenner diode.
FWD
Zenner Di
Di
IGBT
Therefore, installing the active clamp circuits can suppress the spike voltage. Moreover, avalanche
current generated by breakdown of Zenner diode, charge the gate capacitance so as to turn-on the
IGBT. As the result, d
i
/d
t
at turn-off become lower than that before adding the clamp circuit. (Refer to
Fig. 5-8.) Therefore, because switching loss may be increased, apply the clamp circuit after various
confirmations for design of the equipment.
With clamp circuit
Without clamp circuit
V
GE
I
C
V
CE
