US 4,358,730 AGranted

AC Power control circuit

AssigneeEssex Group, Inc.

InventorBrian L. Beifus

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Abstract

An improved control circuit for accurately regulating the power from a supply of unregulated AC voltage to a load, such as a fan motor, via a signal responsive conduction-control switch. The circuit employs first and second comparators. One input to the first comparator is a DC signal representative of desired power level. The other input of the first comparator is a signal having a DC component and a ripple component. The output of the first comparator is a rectangular waveform having a duty factor which is a function of the desired power level relative to the reference load power level. The first comparator output is integrated and then supplied as an input to the second comparator. A sawtooth signal of constant DC level provides the other input to the second comparator. The sawtooth is a submultiple, or preferably a multiple of the AC supply frequency. The output of the second comparator is another rectangular waveform, the duty factor of which is a function of the DC level of the integrated signal and is used to control the conduction timing of the conduction control switch. Preferably, the combined DC-with ripple-signal input of the first comparator is provided by feedback from the second comparator output which is passed through a voltage scaling network connected to an unregulated DC supply. The time constants of the closed loop are selected to provide a temporary power overshoot when increasing the power level. Supplemental limit circuits provide limit signals directly to the second comparator input.

A control circuit for accurately regulating the power to a load which is selectively connected to a power supply of unregulated AC line voltage by a signal responsive conduction-control switch, said control circuit comprising:

means for supplying a first DC signal representative of at least one desired load power level;
means for supplying a second signal comprising a DC level with a periodic ripple, said DC level representing a reference load power level and an automatically adjustable component proportional to the voltage level of said unregulated AC line voltage;
first comparing means having inputs of and being responsive to said first and said second signals for providing a third signal having a square waveform the duty factor of which is a function of said desired power level relative to said reference load power level and compensating for said unregulated AC line voltage level;
means responsive to said third signal for providing a fourth signal having a DC component which is a function of said third signal duty factor;
means for supplying a fifth signal comprising a periodic sawtooth of constant DC level having a repetition rate which is a multiple of submultiple of the frequency of said AC supply;
second comparing means having inputs of and being responsive to said fourth and said fifth signals for providing a sixth signal, said sixth signal being a square waveform varying between two states at the repetition rate of said fifth signal and the duty factor of which is determined by the DC component of said fourth signal such that the timing of transition to and the duration in a particular one of said states thereof is a function of said desired power level relative to said reference load power level and compensated for said unregulated AC line voltage level;
and
means for operatively extending said sixth signal to said conduction switch in a manner to control the conduction timing of said switch at least as a function of the timing of transition to and the duration of said particular one state of said sixth signal.

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Abstract

Claims12