| 摘要 |
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.
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