Abstract: A window heating apparatus for use with an automotive vheicle including a vehicle battery, an internal combustion engine, a transmission, and a generator for generating an output voltage corresponding to engine speed. A voltage regulator is switchably connected to the vehicle battery and, when connected, controls current to the field winding to maintain a constant generator output voltage. A heating element is provided for heating a vehicle window when connected to the generator output terminals. A signal indicative of a demand for heating the vehicle window and a signal indicating when the transmission is in neutral or park are provided. A circuit normally connects the generator output terminal to the vehicle battery and the voltage generator. The circuit, in response to a command signal, connects the generator output terminal to the element while disconnecting the generator output terminal from the vehicle battery and the voltage regulator.

Abstract: In a window heater controlling apparatus used in an automobile, a heater control unit including a microcomputer is employed to detect a heater-ON condition and thereafter to control the heating voltage of the alternator in such a manner that the heating voltage is gradually increased up to the rated heating voltage at the beginning of the heater control operation. This heater control operation can be performed by duty ratio control of the switching transistor.