| 摘要 |
PROBLEM TO BE SOLVED: To make a PTC element diagnosable without flowing an overcurrent in a current range in which no protecting function operates, by providing a current detection circuit for detecting a current value of the PTC element, a power supply circuit for operating on/off in a switching element and a control circuit for controlling the power supply circuit and the current detection circuit. SOLUTION: In a circuit in which a switching element 323 and a PTC element 322 are connected in series, a current detection circuit 328 for detecting a current of the PTC element 322, power supply circuit 326 for operating on/off in the switching element 323 and a control circuit 327 for controlling the current detection circuit and the power circuit are provided. In a CPU provided in the control circuit 327, from a difference of current value measured in each time, a number of measurement or interval of measurement, a changing gradient is calculated. This value is compared with a predetermined normal value, and whether the value stays in a proper range or not, the result can be decided. In this way, in a current range in which no protecting function works, the PTC element can be diagnosed. |
