Switched power supply with current mode regulation
First Claim
1. A switched power supply operating with current mode regulation, comprising:
- a source of input supply voltage;
a transformer;
an output switch coupled to a first winding of said transformer and to said source and responsive to a control signal for initiating a pulse width modulated pulse voltage in a second winding of said transformer in accordance with a switching frequency of said output switch;
a supply circuit including a rectifier coupled to said second winding for generating an operating voltage;
a feedback signal source, having means for monitoring current flowing through said first winding and for monitoring said operating voltage;
a control circuit coupled to said feedback signal source, said control circuit including an oscillator for generating said control signal at a substantially constant frequency during normal operation and at a variable frequency during abnormal operation, said control circuit being responsive to said current and to variations of said operating voltage over a regulating range and in a negative feedback loop, for varying said control signal in a manner that varies the on-time conduction of said output switch within each cycle of said pulse voltage to stabilize said operating voltage; and
,a frequency control for said oscillator responsive to variations of said operating voltage outside of said regulating range, in a positive feedback loop.
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Abstract
A switched mode power supply operating with current mode regulation comprises an output switch coupled to a first winding of a transformer and to a source of input supply voltage. The switch is responsive to a control signal for initiating a pulse width modulated pulse voltage in a second winding of the transformer. A supply circuit coupled to the second winding generates an operating voltage. A feedback signal source monitors both current flowing through the first winding and the operating voltage. A control circuit coupled to the feedback signal source includes an oscillator for generating the control signal at a substantially constant frequency during normal operation and at a variable frequency during abnormal operation. The control circuit is responsive both to the current and to variations of the operating voltage over a regulating range, in a negative feedback loop. The control signal varies the on-time conduction of the output switch in each cycle to stabilize the operating voltage. The oscillator has a frequency control responsive to variations of the operating voltage outside of the regulating range, in a positive feedback loop. The on-time conduction of the output switch is limited to a maximum value by comparing the current to an error signal related to the operating voltage. The error signal varies when the operating voltage is within the regulating range but is limited in magnitude when the operating voltage falls below the regulating range. A DC feedback voltage forms a part of both the negative and positive feedback loops.
128 Citations
28 Claims
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1. A switched power supply operating with current mode regulation, comprising:
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a source of input supply voltage; a transformer; an output switch coupled to a first winding of said transformer and to said source and responsive to a control signal for initiating a pulse width modulated pulse voltage in a second winding of said transformer in accordance with a switching frequency of said output switch; a supply circuit including a rectifier coupled to said second winding for generating an operating voltage; a feedback signal source, having means for monitoring current flowing through said first winding and for monitoring said operating voltage; a control circuit coupled to said feedback signal source, said control circuit including an oscillator for generating said control signal at a substantially constant frequency during normal operation and at a variable frequency during abnormal operation, said control circuit being responsive to said current and to variations of said operating voltage over a regulating range and in a negative feedback loop, for varying said control signal in a manner that varies the on-time conduction of said output switch within each cycle of said pulse voltage to stabilize said operating voltage; and
,a frequency control for said oscillator responsive to variations of said operating voltage outside of said regulating range, in a positive feedback loop. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A switched power supply operating with current mode regulation, comprising:
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a source of input supply voltage; a transformer; an output switch coupled to a first winding of said transformer and to said source and responsive to a control signal for initiating a pulse width modulated pulse voltage in a second winding of said transformer in accordance with a switching frequency of said output switch; a supply circuit including a rectifier coupled to said second winding for generating an operating voltage; a feedback signal source, having means for monitoring current flowing through said first winding and for monitoring said operating voltage; an oscillator for generating said control signal; a control circuit for said oscillator, responsive to an error signal related to variation of said operating voltage in a regulating range for varying said control signal in a manner that varies the on-time conduction of said output switch within each cycle of said pulse voltage to stabilize said operating voltage during normal operation; means for limiting said on-time conduction of said output switch responsive to detection of an error signal value corresponding to said operating voltage falling outside said regulating range; and
,a frequency control for said oscillator for varying the repetition frequency of said control signal such that said switching frequency of said output switch varies when said operating voltage falls outside said regulating range, decreasing with decreasing operating voltage, but otherwise remains substantially constant. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16)
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17. A switched power supply operating with current mode regulation, comprising:
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a source of input supply voltage; a transformer; an output switch coupled to a first winding of said transformer and to said source and responsive to a control signal for initiating a pulse width modulated pulse voltage in a second winding of said transformer in accordance with a switching frequency of said output switch; a supply circuit coupled to said second winding for generating an operating voltage; a feedback signal source, having means for monitoring current flowing through said first winding and for monitoring said operating voltage; and
,a control circuit coupled to said feedback signal source, said control circuit including an oscillator for generating said control signal at a substantially constant frequency during normal operation and at a variable frequency during both a start-up interval and during abnormal operation, said oscillator having a frequency control responsive to a reference signal which remains substantially constant when said operating voltage is within a regulating range during said normal operation but which varies when said operating voltage is outside said regulating range, said control circuit being further responsive to a feedback signal for varying said control signal in a manner that varies the on-time conduction of said output switch within each cycle of said pulse voltage to stabilize said operating voltage within said regulating range during said normal operation. - View Dependent Claims (18, 19, 20, 21, 22)
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23. A switched power supply operating with current mode regulation, comprising:
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a source of input supply voltage; a transformer; an output switch coupled to a first winding of said transformer and to said source and responsive to a control signal for initiating a pulse width modulated pulse voltage in a second winding of said transformer in accordance with a switching frequency of said output switch; a supply circuit coupled to said second winding for generating an operating voltage; an oscillator for generating said control signal; a pulse width control circuit for said oscillator, said pulse width control circuit being responsive to a first feedback loop signal related to said operating voltage for varying said control signal in a manner that varies the on-time of said output switch within each cycle of said pulse voltage to stabilize said operating voltage during normal operation; means for detecting abnormal operation of said power supply; a frequency control circuit for said oscillator responsive to said detecting means and a second feedback loop signal for varying the switching frequency of said control signal during said abnormal operation such that the switching frequency of said output switch decreases with decreasing operating voltage, said frequency control circuit continuously varying the switching frequency between low and high ends of a range; and
,said pulse width control circuit for varying the on-time of said output switch predominating in controlling said output switch at said high end of said range and said frequency control circuit for varying the switching frequency of said output switch predominating at said low end of said range. - View Dependent Claims (24, 25, 26, 27, 28)
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Specification