Appeal No. 95-3876
Application 08/222,009
specification explains (at 20:3-8) that the turning on of
transistor Q3 causes the IGBT to be turned off:
When the transistor Q3 is so switched on, the
gate of the insulated gate bipolar transistor IGBT
is grounded and the insulated gate bipolar
transistor IGBT is therefore switched off. As a
result, no discharge current flow[s] from the flash
tube Xe with the flash firing consequently
interrupted. . . .
The function of transistor Q6, on the other hand, is described
as preventing capacitor C2 in constant voltage source 2 from
discharging through transistor Q3 (Spec. at 20:19-26):
When the transistor Q6 is switched on, the base
of the transistor Q5 is grounded and the transistor
Q5 is therefore switched off, followed by the
switching off of the transistor Q4. Thereby, during
a period in which the flash firing terminating
signal is generated, the discharge of the capacitor
C2 through the transistor Q4, the resistor R8 and
the transistor Q3 can be avoided to minimize any
possible waste of energies.
The specification does not explain why turning off of the IGBT
is attributed to operation of transistor Q3 alone rather than
to the combined operation of transistors Q3 and Q6. The
explanation may be, as appellants seem to be arguing in their
reply brief (at page 2, lines 9-15), that turning on
transistor Q3 quickly discharges the current stored in the
inherent capacitance of the IGBT gate and thus quickly reduces
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