Appeal No. 95-3876
Application 08/222,009
grounding the IGBT collector terminal VC. Because the IGBT
gate has some inherent capacitance, the value of R8 is
selected to be less than or equal to several kilohms in order
to improve the response characteristic (Spec. at 18:21-25).
The grounding of terminal VC of the IGBT has two effects. The
first is to ground one end of the primary and secondary
windings of transformer T2, causing the transformer secondary
to issue a trigger pulse to the flash tube (Spec. at 18:26 to
19:4). The second effect of grounding terminal VC is to clamp
the positive terminal of capacitor C5 of voltage doubling
circuit 6 to ground through resistor R7, thereby causing the
negative terminal of the capacitor to initially apply a
potential of -HV to the lower terminal of the flash tube,
whose upper terminal is connected to the +HV terminal (Spec.
at 19:4-11). Doubling the voltage applied to flash tube in
this manner ensures that the flash tube will be turned on
(Spec. at 19:11-12).
When it is time for the flash to be terminated, a
flash firing terminating signal STOPL is generated by control
circuit 4, which is applied to the bases of transistors Q3 and
Q6 to turn them on (Spec. at 19:13 to 20:2). The
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Last modified: November 3, 2007