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Keith G Kropf

James Dwight Scott

A pulse width modulated dimmer for use with incandescent lamps is powered by a D.C. source that has full on/off capability with a substantially full range of light level control. The dimmer is designed to replace a switch in a lamp circuit in which the lamp is connected on one side to ground and on the other to the switch and then to the power source. The dimmer is designed to operate with a 10 to 30 volt D.C. source. It is controlled in both the on-off mode and in the brightness mode by an N channel field effect transistor switched in response to the voltage level of any remote variable voltage source, such as a potentiometer, photoresistor, phototransistor or digitally controlled voltage source. The lamp is powered through the field effect transistor which is in turn controlled by a comparator which compares the user or automatically variable control voltage level with a triangle wave ramp signal to control the on-off duty cycle and thus the brightness levels of the lamp. When the user or automatically variable voltage source is adjusted high, the field effect transistor is off and the lamp is off. If the user controlled voltage is set very low, the field effect transistor is fully on and the lamp is operated at the D.C. source voltage less the small voltage drop across the field effect transistor. As the user variable voltage is adjusted between the 'off' and 'on' conditions, the duty cycle of the field effect transistor will decrease as the variable voltage is increased, thus dimming the lamps.

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Seneca, MO, United States of America

Keith G Kropf