To safely stop an apparatus, even when failure of a component such as an insulting element or the like is generated by a method, wherein a means by which the feedback signal of an output voltage to be transmitted via a photocoupler is detected so as to be divided into three levels, i.e., the stop state, the normal control state and the abnormal state of a converter.
A feedback signal VFB is divided into three regions by two threshold levels as a high-side threshold voltage VFBsc and a low-side threshold voltage VFBthL. They are set sequentially as a stop operating range (C), a normal operating range (D) and an abnormal operating range (E) from a lower voltage. When a failure is generated in a photocoupler or the like, the feedback signal VFB is deflected fully to high side. In this case, when the feedback signal VFB exceeds the high-side threshold voltage VFBsc, the output of a comparator is set to an H-level, and a timer latch circuit starts to charge a capacitor. Then, when the voltage exceeds a prescribed value, a primary-side shutdown signal is latch-outputted, and a PWM control circuit is maintained in a stop state.
MATSUMURA HIDEAKI
OE TAKUMI
NAKANISHI IWAO
