Bootstrap capacitor refresh circuit
First Claim
1. A bootstrap capacitor charging circuit comprising:
- first and second power switching transistors arranged in a half bridge arrangement such that the first and second transistors are disposed between a high side potential and a low side potential;
a driver circuit for driving the first and second transistors;
a bootstrap capacitor adapted to be charged from a potential source and for providing a voltage source to power an electronic circuit;
a charging circuit providing a charging path from one of said high and low side potentials to said bootstrap capacitor;
first and second series connected switches arranged between a common node of said first and second transistors and one of said high and low side potential;
the bootstrap capacitor having a first terminal coupled to be charged by said charging circuit and a second terminal coupled to a common node between said first and second series connected switches; and
a control circuit operating in first and second modes, wherein in a first mode when said first and second power switching transistors are switching at a rate above a predetermined frequency, a first of said switches connected to said common node of said first and second power switching transistors is controlled on and said second switch is controlled off; and
wherein;
when said first power switching transistor is on for a duration of time exceeding a preset duration, said control circuit operates in a second mode wherein said first and second switches are alternately turned on and off for first and second predefined periods of time whereby the bootstrap capacitor charges through said second switch and said charging circuit during the second predefined period of time.
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Accused Products
Abstract
A bootstrap capacitor charging circuit comprising first and second power switching transistors arranged in a half bridge arrangement such that the first and second transistors are disposed between a high side potential and a low side potential, a driver circuit for driving the first and second transistors, a bootstrap capacitor adapted to be charged from a potential source and for providing a voltage source to power an electronic circuit, a charging circuit providing a charging path from one of the high and low side potentials to the bootstrap capacitor, first and second series connected switches arranged between a common node of the first and second transistors and one of the high and low side potential, the bootstrap capacitor having a first terminal coupled to be charged by the charging circuit and a second terminal coupled to a common node between the first and second series connected switches; and a control circuit operating in first and second modes, wherein in a first mode when the first and second power switching transistors are switching at a rate above a predetermined frequency, a first of the switches connected to the common node of the first and second power switching transistors is controlled on and the second switch is controlled off; and wherein, when the first power switching transistor is on for a duration of time exceeding a preset duration, the control circuit operates in a second mode wherein the first and second switches are alternately turned on and off for first and second predefined periods of time whereby the bootstrap capacitor charges through the second switch and the charging circuit during the second predefined period of time.
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Citations
9 Claims
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1. A bootstrap capacitor charging circuit comprising:
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first and second power switching transistors arranged in a half bridge arrangement such that the first and second transistors are disposed between a high side potential and a low side potential;
a driver circuit for driving the first and second transistors;
a bootstrap capacitor adapted to be charged from a potential source and for providing a voltage source to power an electronic circuit;
a charging circuit providing a charging path from one of said high and low side potentials to said bootstrap capacitor;
first and second series connected switches arranged between a common node of said first and second transistors and one of said high and low side potential;
the bootstrap capacitor having a first terminal coupled to be charged by said charging circuit and a second terminal coupled to a common node between said first and second series connected switches; and
a control circuit operating in first and second modes, wherein in a first mode when said first and second power switching transistors are switching at a rate above a predetermined frequency, a first of said switches connected to said common node of said first and second power switching transistors is controlled on and said second switch is controlled off; and
wherein;
when said first power switching transistor is on for a duration of time exceeding a preset duration, said control circuit operates in a second mode wherein said first and second switches are alternately turned on and off for first and second predefined periods of time whereby the bootstrap capacitor charges through said second switch and said charging circuit during the second predefined period of time. - View Dependent Claims (2, 3, 4, 5, 7, 9)
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6. A method for charging a bootstrap capacitor in a circuit comprising first and second power switching transistors arranged in a half bridge arrangement such that the first and second transistors are disposed between a high side potential and a low side potential, a driver circuit for driving the first and second transistors;
- a bootstrap capacitor adapted to be charged from a potential source and for providing a voltage source to power an electronic circuit;
a charging circuit providing a charging path from one of said high and low side potentials to said bootstrap capacitor, first and second series connected switches arranged between a common node of said first and second transistors and one of said high and low side potential;
the bootstrap capacitor having a first terminal coupled to be charged by said charging circuit and a second terminal coupled to a common node between said first and second series connected switches; and
a control circuit for controlling the first and second switches, the method comprising;
operating said first and second switches in a first mode when said first and second power switching transistors are switching at a rate above a predetermined frequency, such that a first of said switches connected to said common node of said first and second power switching transistors is controlled on and said second switch is controlled off; and
operating said first and second switches in a second mode when said first power switching transistor is on for a duration of time exceeding a preset duration, such that said first and second switches are alternately turned on and off for first and second predefined periods of time whereby the bootstrap capacitor charges through said second switch and said charging circuit during the second predefined period of time. - View Dependent Claims (8)
- a bootstrap capacitor adapted to be charged from a potential source and for providing a voltage source to power an electronic circuit;
Specification