Capacitor charging methods and apparatus
First Claim
1. Apparatus for measuring the output voltage of a capacitor charging circuit having a transformer with a primary winding coupled to a switch and a secondary winding, comprising:
- a filter coupled to the switch to filter a voltage at the switch to provide a filtered signal; and
a comparator having a first input responsive to the filtered signal, a second input coupled to a reference voltage, and an output at which is provided a control signal indicative of whether an output voltage of the capacitor charging circuit has reached a desired level.
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Accused Products
Abstract
A capacitor charging circuit is provided with a primary side output voltage sensing circuit for generating a control signal indicative of whether the output voltage has reached a desired level. The control signal is unaffected by voltage spikes occurring when the main switch is turned off. In one embodiment, the circuit filters the primary side voltage for comparison to a reference voltage in order to provide the control signal. In another embodiment, an AND gate provides the control signal indicating that the output voltage has reached the desired level only in response to the primary side voltage being greater than a reference voltage and the secondary current being discontinuous. In a further embodiment, an AND gate provides the control signal indicating that the output voltage has reached the desired levels only in response to a predetermined delay occurring after the primary side voltage becomes greater than a reference voltage and the secondary current being discontinuous. According to a further aspect of the invention, an auxiliary switch is provided to reduce the reverse recovery time of the output diode in order to speed up the capacitor charging time.
53 Citations
16 Claims
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1. Apparatus for measuring the output voltage of a capacitor charging circuit having a transformer with a primary winding coupled to a switch and a secondary winding, comprising:
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a filter coupled to the switch to filter a voltage at the switch to provide a filtered signal; and
a comparator having a first input responsive to the filtered signal, a second input coupled to a reference voltage, and an output at which is provided a control signal indicative of whether an output voltage of the capacitor charging circuit has reached a desired level. - View Dependent Claims (2, 3, 4, 5, 6)
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7. Apparatus for measuring the output voltage of a capacitor charging circuit having a transformer with a primary winding coupled to a switch and a secondary winding coupled to the capacitor, comprising:
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a comparator having a first input coupled to the switch, a second input coupled to a reference voltage, and an output at which is provided an output signal indicative of whether a voltage at the switch exceeds the reference voltage;
a current sensing circuit for sensing a current level in the secondary winding; and
a logic gate having a first input coupled to the output of the comparator, a second input coupled to the current sensing circuit and an output at which is provided a control signal indicative of the output voltage reaching a desired level only when (a) the switch voltage exceeds the reference voltage and (b) the current level in the secondary winding reaches approximately zero amps. - View Dependent Claims (8, 9, 10)
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11. Apparatus for measuring the output voltage of a capacitor charging circuit having a transformer with a primary winding coupled to a switch and a secondary winding coupled to the capacitor, comprising:
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a first comparator having a first input coupled to the switch, a second input coupled to a first reference voltage, and an output at which is provided a first comparator output signal indicative of whether a voltage at the switch exceeds the first reference voltage;
a delay element coupled to the first comparator output for providing a delayed output signal that is a delayed version of the first comparator output signal;
a second comparator having a first input coupled to the switch, a second input coupled to a second reference voltage, and an output at which is provided an output signal indicative of whether the switch voltage exceeds the second reference voltage; and
a logic gate having a first input coupled to the output of the delay element, a second input coupled to the output of the second comparator, and an output at which is provided a control signal indicative of the output voltage reaching a desired level only when (a) a delay has occurred since the switch voltage exceeded the first reference voltage and (b) the second reference voltage exceeds the switch voltage. - View Dependent Claims (12, 13)
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14. A capacitor charging circuit having a transformer with a primary winding coupled to a main switch and a secondary winding coupled to the capacitor, comprising:
an auxiliary switch coupled in parallel with the main switch and adapted to be on when a current through the capacitor is less than a predetermined level and off when the capacitor current is greater than the predetermined level. - View Dependent Claims (15, 16)
Specification