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A method and a circuit for protecting an electric motor and/or its trigger circuit against overload in the emergency-operation mode in a motor vehicle direct-current fan motor operated by means of pulse width modulation, in which the trigger circuit is designed as an emergency-operation controller,

A method and a circuit for protecting an electric motor and/or its trigger circuit against overload in the emergency-operation mode in a motor vehicle direct-current fan motor operated by means of pulse width modulation, in which the trigger circuit is designed as an emergency-operation controller, with a microcontroller preceding the motor end stage and with a comparator assembly for detecting overvoltages. Overload protection is assured at elevated battery voltage and at the same time when the emergency-operation controller is activated in response to malfunctions in the normal triggering of the electric motor. To that end, at least one overvoltage threshold (Us1, U s2) is defined; when it is exceeded, the power supplied to the motor is reduced or switched off.

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The invention claimed is: 1. A method of activation of an emergency operation controller for protecting an electric motor (10) and/or its trigger circuit (12) against overload, wherein the electric motor is assigned a motor end stage for pulse-width modulated control (PWM) of the power supplied and

The invention claimed is: 1. A method of activation of an emergency operation controller for protecting an electric motor (10) and/or its trigger circuit (12) against overload, wherein the electric motor is assigned a motor end stage for pulse-width modulated control (PWM) of the power supplied and is also assigned a controller for limiting the motor power on the occurrence of an elevated supply voltage, the method comprising providing an overload protection which becomes operative in emergency operation of the electric motor (10) by activation of an emergency operation controller (14, 16) upon the occurrence of a malfunction (28, 30) in the triggering circuit ( 12) of the motor end stage, and supplying electric motor (10) with a defined emergency-operation power, which below a first overvoltage threshold (Us1) of the supply voltage has a specified value or course and is reduced or switched off if one or more overvoltage thresholds (Us1 Us2) are exceeded. 2. The method of claim 1, comprising supplying the electric motor (10) with a power corresponding to the range between 30% and 100% of the battery voltage (Ubat), below the first overvoltage threshold (Us1), and in particular a power corresponding to the full battery voltage (Ubat). 3. The method of claim 2, further comprising specifying two overvoltage thresholds (Us1, Us2), and between the first threshold (Us1) and the second threshold (Us2), supplying the electric motor (10) with a power corresponding to the range between 30% and 70% of the battery voltage (Ubat), and preferably a power corresponding to half the battery voltage. 4. The method of claim 2, further comprising switching the electric motor (10) off when the second overvoltage threshold (Us2) is reached. 5. The method of claim 2, wherein the electric motor circuit is a 12-volt on-board electrical system of a motor vehicle, and wherein the first overvoltage threshold (Us1) is fixed at a value of 14 V. 6. The method of claim 2, wherein the electric motor circuit is a 12-volt on-board electrical system of a motor vehicle, and wherein the second overvoltage threshold (Us2) is fixed at a value of 16 V. 7. The method of claim 1, further comprising specifying two overvoltage thresholds (Us1, Us2), and between the first threshold (Us1) and the second threshold (Us2), supplying the electric motor (10) with a power corresponding to the range between 30% and 70% of the battery voltage (Ubat), and preferably a power corresponding to half the battery voltage. 8. The method of claim 7, further comprising switching the electric motor (10) off when the second overvoltage threshold (Us2) is reached. 9. The method of claim 7, wherein the electric motor circuit is a 12-volt on-board electrical system of a motor vehicle, and wherein the first overvoltage threshold (Us1) is fixed at a value of 14 V. 10. The method of claim 7, wherein the electric motor circuit is a 12-volt onboard electrical system of a motor vehicle, and wherein the second overvoltage threshold (Us2) is fixed at a value of 16 V. 11. The method of claim 1, further comprising switching the electric motor (10) off when the second overvoltage threshold (Us2) is reached. 12. The method of claim 11, wherein the electric motor circuit is a 12-volt on-board electrical system of a motor vehicle, and wherein the first overvoltage threshold (Us1) is fixed at a value of 14 V. 13. The method of claim 11, wherein the electric motor circuit is a 12-volt on-board electrical system of a motor vehicle, and wherein the second overvoltage threshold (Us2) is fixed at a value of 16 V. 14. The method of claim 1, wherein the electric motor circuit is a 12-volt onboard electrical system of a motor vehicle, and wherein the first overvoltage threshold (Us1) is fixed at a value of 14 V. 15. The method of claim 1, wherein the electric motor circuit is a 12-volt on-board electrical system of a motor vehicle, and wherein the second overvoltage threshold (Us2) is fixed at a value of 16 V. 16. A method of activation of an emergency operation controller for protecting an electric motor (10) and/or its trigger circuit (12) against overload, wherein the electric motor is assigned a motor end stage for pulse-width modulated control (PWM) of the power supplied and is also assigned a controller for limiting the motor power on the occurrence of an elevated supply voltage, the method comprising providing an overload protection which becomes operative in emergency operation of the electric motor (10) by activation of an emergency operation controller (14, 16) upon the occurrence of a malfunction (28, 30) in the triggering circuit ( 12) of the motor end stage, and supplying electric motor (10) with a defined emergency-operation power, which below a first overvoltage threshold Us1 of the supply voltage has a specified value or course and is reduced or switched off if one or more overvoltage thresholds (Us1 Us2) are exceeded, further comprising regulating the power of the electric motor (10) in the emergency-operation mode by means of a voltage monitoring circuit with a comparator assembly (14), to which a reference voltage (Uref) corresponding to the battery voltage (Ubat) is supplied as a reference value for the overvoltage thresholds (Us1, Us2 ). 17. In a circuit arrangement for protecting an electric motor and/or its trigger circuit (12) against overload, the circuit arrangement comprising a motor end stage for pulse-width modulated control (PWM) of the power supplied to the electric motor, a controller for limiting the motor power on the occurrence of an elevated supply voltage, the improvement wherein, for the overload protection in the emergency-operation mode of the electric motor (10), the trigger circuit (12) is embodied as an emergency-operation controller ( 14, 16, 22), which in addition to a PWM set-point value transducer (18) and the motor end stage (22) has a microcontroller (16), which precedes the motor end stage and which upon an interruption or a defective input of the set-point value signal of the pulse width modulation (PWMso11) and/or of a switched supply voltage (U15) supplies a control voltage (PWM) to the motor end stage (22), corresponding to the specification of at least one overvoltage threshold (Us1, Us2) to the microcontroller. 18. The circuit arrangement of claim 17, wherein the emergency-operation controller (14, 16,22) comprises a comparator assembly (14), to which on the one hand a reference voltage (Uref) corresponding to the battery voltage (U bat) and on the other, as a comparison value, at least one overvoltage threshold (Us1, Us2) above the normal battery voltage (Ubat) are specified. 19. The circuit arrangement of claim 18, wherein the electric motor is employed in a 12-volt on-board electrical system of a motor vehicle, and wherein the comparator assembly (14) has two comparators (24, 26), to which on the one hand a reference value (Uref) derived from the actual battery voltage (U bat) and on the other overvoltage thresholds of approximately 14 V (Us1) and approximately 16 V (Us2), respectively, above the normal battery voltage (Ubat) of approximately 13 V, are specified. 20. The circuit arrangement of claim 19, wherein the electric motor is employed in a 12-volt on-board electrical system of a motor vehicle, and wherein the comparator assembly (14) has two comparators (24, 26), to which on the one hand a reference value (Uref) derived from the actual battery voltage (U bat) and on the other overvoltage thresholds of approximately 14 V (Us1) and approximately 16 V (Us2), respectively, above the normal battery voltage (Ubat) of approximately 13 V, are specified.