| 摘要 |
PROBLEM TO BE SOLVED: To provide a protection circuit which is simple in configuration and is capable of protecting an output control transistor from the overvoltage (surge voltage) of a power source to be applied to a collector. SOLUTION: The protection circuit protects, from the overvoltage of the power source, a base voltage drive output control transistor 15 the collector of which is connected with a load (control target) 50 connected with the power source and in which voltage for controlling the load is inputted to a base. The protection circuit is provided with an overvoltage protection circuit 20 including: a first current detection means 22 for detecting the collector current of the output control transistor 15; a comparison means 25 for comparing voltage variation by the detected collector current with preset first reference voltage Vref1; and base voltage cutoff means 30, 35 for making base voltage zero when the voltage variation detected on the basis of the overvoltage is higher than the first reference voltage. COPYRIGHT: (C)2005,JPO&NCIPI
|
