OVERCURRENT/OVERVOLTAGE PROTECTIVE CIRCUIT FOR SWITCHING POWER SUPPLY

摘要

PURPOSE: To provide a switching circuit utilizing an overvoltage protective circuit for overcurrent protection for an output line from an independent winding in order to produce output efficiently from the independent winding in which overcurrent protective function is exhibited accurately without requiring quite severe troublesome circuit design. ;CONSTITUTION: An overvoltage protective circuit 9 comprising Zener diodes ZD₂, ZD₃ and a LED PD₁ in a first photocoupler PC₁ is utilized for overcurrent protection for an output line 6 from an independent winding. When the LED PD₁ emits light, a photothyristor PT₁ is conducted and oscillation at DC-DC converter section 3 is stopped. When overcurrent flows through the independent winding output line 6, Zener diode ZD₄ is interrupted due to voltage drop and an overcurrent detection transistor Q₄ is turned OFF. Consequently, a LED PD₂ in a second photocoupler PC₂ emits light to conduct a phototransistor PT₂ thus causing the LED PD. in the first photocoupler PC₁ to emit light.;COPYRIGHT: (C)1994,JPO&Japio