Dimmer having a power supply monitoring circuit
First Claim
1. A two-wire dimmer for control of a lighting load from a source of AC voltage, comprising:
- a semiconductor switch operable to be connected between said lighting load and said source of AC voltage;
said semiconductor switch having a conducting state and a non-conducting state;
a power supply operable to draw current from said source of AC voltage when said semiconductor switch is in said non-conducting state; and
a control circuit operable to control said semiconductor switch into said conducting state for an on-time each half-cycle of said AC voltage;
said control circuit coupled to an input of said power supply for monitoring a voltage of said power supply;
wherein said control circuit is operable to decrease said on-time when said input voltage of said power supply falls below a first predetermined voltage threshold.
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Abstract
A two-wire dimmer for control of a lighting load from an alternating-current (AC) power source includes a semiconductor switch, a power supply, and a control circuit. The power supply includes an energy storage input capacitor that is able to charge only when the semiconductor switch is non-conductive. The control circuit continuously monitors the voltage on the input capacitor and automatically decreases the maximum allowable conduction time of the semiconductor switch when the voltage falls to a level that will not guarantee proper operation of the power supply. The dimmer of the present invention is able to provide the maximum possible conduction time of the semiconductor switch at high end (i.e., maximum light intensity) while simultaneously ensuring sufficient charging time for proper operation of the power supply, and hence, the dimmer.
138 Citations
10 Claims
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1. A two-wire dimmer for control of a lighting load from a source of AC voltage, comprising:
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a semiconductor switch operable to be connected between said lighting load and said source of AC voltage;
said semiconductor switch having a conducting state and a non-conducting state;a power supply operable to draw current from said source of AC voltage when said semiconductor switch is in said non-conducting state; and a control circuit operable to control said semiconductor switch into said conducting state for an on-time each half-cycle of said AC voltage;
said control circuit coupled to an input of said power supply for monitoring a voltage of said power supply;wherein said control circuit is operable to decrease said on-time when said input voltage of said power supply falls below a first predetermined voltage threshold. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method for controlling the intensity of a lighting load from a source of AC voltage in a dimmer comprising a semiconductor switch coupled between said lighting load and said source, a control circuit for controlling said semiconductor switch, and a power supply for powering said control circuit;
- said method comprising the steps of;
scaling down a voltage of said power supply to produce a sense voltage; measuring said sense voltage; comparing the sense voltage to a first predetermined voltage threshold; and changing a conduction time of said semiconductor switch based on the result of the step of comparing. - View Dependent Claims (8, 9, 10)
- said method comprising the steps of;
Specification