PURPOSE: To ensure the reliable protection and stable operation by providing a plurality of parts to be protected, different in breakdown voltage and so on, with respective protective elements corresponding thereto and making the protective elements differ in breakdown voltage in correspondence to that and operating voltage of the corresponding parts to be protected.
CONSTITUTION: A capacitive load Lc1, junction load Lj and capacitive load Lc2 are protected through protective circuits 1-3 including protective transistors Q1-Q2, respectively. While the operating and breakdown voltages of the loads Lc1, Lj and Lc2 are as conventional, the breakdown voltages B1-B3 of the protective transistors Q1-Q3 are made differ from one another in correspondence to the operating and breakdown voltages of the loads Lc1, Lj and Lc2. To concretely mention, the breakdown voltages B1-B3 are set to values which are, as required, larger than the maximum values a1-a3 of the operating voltages A1-A3 of the loads to be protected and obtains sufficient breakdown margins E1-E3. This optimally protects the loads Lc1, Lj and Lc2 in correspondence to their breakdown and operating voltages.
HIROTA ISAO
ISONO HIDETO
HIBI HIROSHI
