Switched-mode power supply with compensation for varying input voltage
First Claim
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1. A switched-mode power supply comprising:
- a series arrangement of a controllable switching element, an inductive element and a sensing resistor, means coupling the series arrangement so as to receive an input voltage and to pass a periodically interrupted current by turning the controllable switching element is on and off, means for turning off the controllable switching element in response to a voltage drop produced across the sensing resistor by the current through the sensing resistor, and a further inductive element coupled in series with the sensing resistor so as to generate a voltage which contributes to the voltage drop across the sensing resistor, the current through the further inductive element being always substantially equal to the current through the sensing resistor.
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Abstract
In a switched-mode power supply a coil is periodically connected across an input voltage by means of a switching element. The switching element is turned off when the voltage across a sensing resistor in series with the switching element exceeds a given threshold. The threshold is reached sooner when the input voltage increases. This effect is compensated by an inductive element in series with the sensing resistor, through which inductive element the same current flows as through the sensing resistor.
26 Citations
19 Claims
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1. A switched-mode power supply comprising:
- a series arrangement of a controllable switching element, an inductive element and a sensing resistor, means coupling the series arrangement so as to receive an input voltage and to pass a periodically interrupted current by turning the controllable switching element is on and off, means for turning off the controllable switching element in response to a voltage drop produced across the sensing resistor by the current through the sensing resistor, and a further inductive element coupled in series with the sensing resistor so as to generate a voltage which contributes to the voltage drop across the sensing resistor, the current through the further inductive element being always substantially equal to the current through the sensing resistor.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A self-oscillating switched mode power supply comprising:
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a pair of input terminals for connection to a source of supply voltage for the switched mode power supply, a series circuit including a controllable switching means, an inductive element and a sensing resistor coupled to said pair of input terminals, a positive feedback circuit coupled to a control electrode of the controllable switching means and responsive to a current flowing in said series circuit for driving said controllable switching means into conduction, a further inductive element connected in series with the sensing resistor so as to produce a voltage which adds to the voltage drop across the sensing resistor, wherein the current flow through the further inductive element is equal to the current flow through the sensing resistor, and means responsive to the combined voltage across the sensing resistor and the further inductive element for turning off conduction through the controllable switching means. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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Specification