Sample-and-hold circuit for a switched-mode power supply
First Claim
1. A sample-and-hold circuit for a switched-mode power supply having a transformer with a primary winding, an auxiliary winding and a secondary winding, a switching transistor coupled in series with the primary winding, and a sample-and-hold capacitor for storing a voltage proportional to an output voltage of said auxiliary winding and coupled to a control terminal of said switching transistor in a feedback loop which normally operates in a closed-loop mode for switchably regulating said switched-mode power supply, characterized in that said circuit comprises a discharge capacitor switchably coupled in parallel with said sample-and-hold capacitor for discharging excess voltage that will drive said feedback loop into an open-loop mode of operation from said sample-and-hold capacitor to restore said feedback loop to said closed-loop mode of operation.
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Accused Products
Abstract
A sample-and-hold circuit is provided for a switched-mode power supply of the type having a transformer with a primary winding, an auxiliary winding and a secondary winding, with a switching transistor coupled in series with the primary winding and a sample-and-hold capacitor for storing a voltage proportional to an output voltage of the auxiliary winding and coupled to a controlled terminal of the switching transistor in a feedback loop which normally operates in a closed-loop mode for switchably regulating the power supply. To prevent the feedback loop from being driven to an open-loop or "stuck" mode of operation, a discharge capacitor is provided which is switchably coupled in parallel with the sample-and-hold capacitor to discharge excess voltage from the sample-and-hold capacitor and thereby restore the feedback loop to its normal closed-loop operating mode.
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Citations
5 Claims
- 1. A sample-and-hold circuit for a switched-mode power supply having a transformer with a primary winding, an auxiliary winding and a secondary winding, a switching transistor coupled in series with the primary winding, and a sample-and-hold capacitor for storing a voltage proportional to an output voltage of said auxiliary winding and coupled to a control terminal of said switching transistor in a feedback loop which normally operates in a closed-loop mode for switchably regulating said switched-mode power supply, characterized in that said circuit comprises a discharge capacitor switchably coupled in parallel with said sample-and-hold capacitor for discharging excess voltage that will drive said feedback loop into an open-loop mode of operation from said sample-and-hold capacitor to restore said feedback loop to said closed-loop mode of operation.
Specification