Appeal No. 1997-2340 Page 2
Application No. 08/329,687
paths including VBO free thyristors to protect against the
over-
voltage. The thyristors are switched on, i.e., fired, by a
gate or fire by themselves, i.e., self-fire, to relieve over-
voltage.
Randomness between the self-firing voltages of the
individual thyristors and temperature variations can cause
current flow to become concentrated in one of the parallel
circuits. To prevent such a condition, heretofore,
temperature control and VB0 free thyristors having identical
characteristics had to be used in over-voltage protection
devices. Consequently, such devices were bulky and costly.
In contrast, a sensor in the inventive protection device
detects the self-firing of a thyristor in any one of its
parallel current paths. Upon such detection, a gate fires all
the other thyristors. Firing all the thyristors allows
current to flow through all the current paths thereby
distributing the excessive current between the various paths.
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