Protected zero-crossing detection using switching transistor's on-resistance
First Claim
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1. A circuit, comprising:
- first and second power transistors connected to turn on and turn off together;
a first voltage-sensing stage which is operatively connected, through current-carrying terminals of said second transistor, to sense the voltage across current-carrying terminals of said first transistor;
said first voltage-sensing stage being implemented without a type of transistor of said first transistor;
wherein said first transistor is connected to interrupt a load current;
whereby said second transistor protects said first voltage-sensing stage from voltages which may appear on said first transistor when said first transistor is off.
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Abstract
An auxiliary power transistor which is switched in common with the primary power transistor, and which isolates the voltage-monitoring circuit when the primary power transistor is off. Thus the signal for sensing the secondary current is connected only when the power transistor is turned on, and high voltages in the sensing logic are avoided. This is particularly advantageous for systems where the turn-off times of the power transistor are sought to be synchronized with current zero-crossings. This current-zero-crossing technique may be used to detect zero-crossings of current on a secondary-side switch.
116 Citations
38 Claims
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1. A circuit, comprising:
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first and second power transistors connected to turn on and turn off together; a first voltage-sensing stage which is operatively connected, through current-carrying terminals of said second transistor, to sense the voltage across current-carrying terminals of said first transistor; said first voltage-sensing stage being implemented without a type of transistor of said first transistor; wherein said first transistor is connected to interrupt a load current; whereby said second transistor protects said first voltage-sensing stage from voltages which may appear on said first transistor when said first transistor is off. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A circuit, comprising:
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first and second power transistors having respective control terminals thereof operatively connected in common; a first voltage-sensing stage having at least one input thereof operatively connected through current-carrying terminals of said second transistor to one of at least two current-carrying terminals of said first transistor, said first voltage-sensing stage being connected to detect zero-crossings in the voltage across said current-carrying terminals of said first transistor when said transistors are both on; said transistors both being implemented without a type of transistor of said first voltage-sensing stage; wherein said first transistor is connected to interrupt a load current; whereby said second transistor protects said first voltage-sensing stage from voltages which may appear on said first transistor when said first transistor is off. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A computer system, comprising:
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memory, and a microprocessor operatively connected to read and write said memory; a graphics controller connected to said microprocessor; a video display connected to said graphics controller; and a power supply, comprising first and second power transistors connected to turn on and turn off together; a voltage-sensing stage which is operatively connected, through current-carrying terminals of said second transistor, to sense the voltage across current-carrying terminals of said first transistor;
said voltage-sensing stage being at least partly implemented using a device type different from that of said first transistor;wherein said first transistor is connected to interrupt a load current; whereby said second transistor protects said voltage-sensing stage from voltages which may appear on said first transistor when said first transistor is off. - View Dependent Claims (24, 25, 26, 27, 28)
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29. A method for zero-crossing detection of currents in power circuits, comprising the steps of:
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(a.) isolating a first power transistor from a first voltage-monitoring circuit with a second power transistor, which is switched on only when said first power transistor is switched on;
said first power transistor also being used for switching a load current; and(b.) when said second power transistor is on, detecting zero-crossings of said load current by detecting zero-crossings of a voltage on an on-resistance of said first power transistor, using said first voltage-monitoring circuit. - View Dependent Claims (30, 31, 32, 33)
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34. A circuit for zero-crossing detection of currents in power circuits, comprising:
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means for isolating a first power transistor from a first voltage-monitoring circuit with a second power transistor, which is switched on only when said first power transistor is switched on; said first power transistor also being connected to switch a load current; and means for detecting zero-crossings of said load current by detecting zero-crossings of a voltage on an on-resistance of said first power transistor, using said first voltage-monitoring circuit, when said second power transistor is on. - View Dependent Claims (35, 36, 37, 38)
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Specification