CAPACITOR CHARGING METHODS AND APPARATUS
First Claim
1. In a capacitor charging circuit having a transformer with a primary winding coupled to a switch and a secondary winding coupled to an output capacitor, apparatus comprising:
- an RC network on a primary side of the transformer associated with the primary winding and having an RC time constant with a predetermined relationship to an RC time constant associated with the output capacitor, and wherein a regulation voltage is provided across the RC network; and
a control circuit responsive to the regulation voltage for providing an enable signal to enable a charging mode during which the switch is turned on and off to charge the output capacitor and to disable the charging mode.
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Accused Products
Abstract
A capacitor charging circuit is provided with a primary side output voltage sensing circuit including an RC network having an RC time constant with a predetermined relationship to the RC time constant of the output capacitor. Once the capacitor voltage reaches a fully charged level, the charging mode is terminated. The output voltage is continuously detected by measuring the voltage across the primary side RC network that decays at a predetermined rate with respect to the output capacitor and the charging mode is commenced once the RC voltage falls to a predetermined level. According to a further aspect of the invention, a switch control circuit in a flyback converter controls the switch off time in response to detection of a change in the slope polarity of the voltage at a terminal of the switch.
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Citations
24 Claims
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1. In a capacitor charging circuit having a transformer with a primary winding coupled to a switch and a secondary winding coupled to an output capacitor, apparatus comprising:
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an RC network on a primary side of the transformer associated with the primary winding and having an RC time constant with a predetermined relationship to an RC time constant associated with the output capacitor, and wherein a regulation voltage is provided across the RC network; and
a control circuit responsive to the regulation voltage for providing an enable signal to enable a charging mode during which the switch is turned on and off to charge the output capacitor and to disable the charging mode. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. In a capacitor charging circuit having a transformer with a primary winding coupled to a switch and a secondary winding coupled to an output capacitor across which an output voltage is provided, a method for maintaining the output capacitor in a substantially fully-charged condition, comprising:
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detecting the output voltage from the primary side of the transformer by measuring a voltage across an RC network that discharges at a rate that has a predetermined relationship to a rate of discharge of the output capacitor; and
commencing a charging mode of operation during which the switch is turned on and off to charge the output capacitor in response to the voltage across the RC network falling to a predetermined level. - View Dependent Claims (13)
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14. A flyback converter comprising:
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a transformer having a primary winding and a secondary winding;
a switch having a terminal coupled to the primary winding; and
a switch control circuit having a first circuit portion for controlling the on time of the switch and a second circuit portion for controlling the off time of the switch, wherein the second circuit portion comprises a slope detection circuit to detect a change in the polarity of the voltage at the switch terminal. - View Dependent Claims (15, 16, 17, 18, 19)
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20. In a flyback converter having a transformer with a primary winding coupled to a switch and a secondary winding, a method comprising:
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detecting of a change in the polarity of the slope of a voltage at a terminal of the switch; and
turning the switch on in response to the detection. - View Dependent Claims (21, 22, 23, 24)
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Specification