Patent ID: 7064553

Claim:
An open-circuit detecting circuit comprising: a driving circuit for controlling power supply to a load; an on-off signal generating circuit for generating a on-off signal for controlling power supply to the driving circuit; a current detecting circuit for converting current flowing from the driving circuit to the load to a voltage; a comparator circuit for comparing the voltage with a reference voltage and outputs a signal according to a result of the comparison; and a storage circuit for storing the result of the comparison until a falling edge appears in the on-off signal wherein: the driving circuit is a switch connected between a power source and the load; the current detecting circuit obtains a voltage calculated by subtracting a voltage drop at the driving circuit from a source voltage, determines the calculated voltage as the voltage converted from the current flowing from the driving circuit to the load, and outputs the calculated voltage to the comparator circuit; the load is a light emitting diode indicator unit having a plurality of lines of light emitting diodes, the lines connected in parallel to each other; and the reference voltage is set to a voltage calculated by adding a variation in a voltage drop at the driving circuit when a predetermined number of light emitting diode lines become open to the voltage converted from the current flowing from the driving circuit to the load.