Anden Co., Ltd.

Denso Corporation

Takeyoshi Hisada

Fukuo Ishikawa

Nobutomo Takagi

Akira Sugiura

Shigekazu Sugimoto

Ippei Kawamoto

An overcurrent protection circuit includes a load drive section driving a load, a wire coupled with the load and the load drive section, a current detection section detecting a load current value of an electric current that flows to the load, an addition and subtraction section determining an addition and subtraction value based on the load current value and transmitting an integration result of addition and subtraction, a comparison circuit comparing the integration result with a threshold value, and a control circuit controlling the load drive section based on the comparison result. The addition and subtraction section includes an addition value determination circuit that determines an addition value in the addition and subtraction value based on the load current value and a function expression or information indicating a relationship between the load current value and the addition value.

Overcurrent protection circuit

An overcurrent protection circuit includes a load driver for driving a load, a controller for turning ON and OFF the load driver, a current sensor for measuring a load current flowing through the load, and an add/subtract circuit for performing both an addition operation and a subtraction operation on a previous calculation result or for performing only the subtraction operation on the previous calculation result so as to produce a present calculation result. The addition operation uses an added value depending on the presently measured current. The subtraction operation uses a subtracted value depending on the presently measured current. The controller turns OFF the load driver, when the present calculation result of the add/subtract circuit exceeds a predetermined determination value.

In a temperature protection device for power devices of the present invention, detected temperatures of power devices are compared with respective threshold values by determination units. If either one of the determination units determines that there is abnormal heat build-up of the respective power devices, the output of that determination units is maintained by a latch circuit, and the current carried by the power device subject to abnormal heat build-up is interrupted. In addition, due to the output of the determination units making the determination, the threshold value of the other determination units is changed to a temperature threshold value that is higher than that set previously, so that it is not determined that the normally operating power device is subject to abnormal heat build-up. This changing of the threshold value is only executed for a fixed time period based upon a timer circuit.

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Hekinan, Japan

Takeyoshi Hisada