Appeal No. 95-3876
Application 08/222,009
circuit (24 and 25), trigger means (33), [and] control means
(23)" (August 2, 1993, Office action at 3). The examiner
contends, and appellants do not dispute, that it would have
been obvious in view of the Hayashi reference to replace
Iwata's FET 15 with an IGBT; instead, appellants contend their
claims do not read on Iwata thus modified. Specifically, with
respect to independent claim 14 they argue (Brief at 5, lines
4-14):
In contrast to the arrangement disclosed in the
Iwata et al[.] patent, in the circuit of the present
invention the voltage at the gate of the IGBT is
positively removed, so that flash firing quickly
stops and the amount of emitted flash light is more
accurately controlled. Referring to the circuit of
Figure 1, for example, when the firing of the flash
is to be terminated, a logic high signal is
generated at the STOP terminal of the control
circuit 4. This signal renders the transistor Q6
conducting, which in turn brings the transistors Q5
and Q4 into a non-conducting state. As a result,
the supply of voltage from the capacitor C2 to the
gate of the IGBT is interrupted. At the same time,
the transistor Q3 is brought into a conducting
state, to lower the voltage at the gate of the IGBT,
thereby removing any capacitance component.
Consequently, the IGBT is immediately turned off,
and the flash is promptly extinguished.
The Iwata et al[.] patent does not disclose, nor
otherwise suggest, this concept of removing an
enabling voltage at the gate of the FET in response
to a flash terminating command, as recited in claim
14. Substituting an insulated gate bipolar
transistor for the FET 15, as suggested in the final
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