Load detecting circuits and the method thereof
First Claim
1. A no-load detecting circuit for a switching mode power supply, comprising:
- a variable resistance circuit coupled between the switching mode power supply and a load of the switching mode power supply, wherein an equivalent resistance of the variable resistance circuit will vary depending on the status of the load of the switching mode power supply; and
a first comparison circuit coupled to the variable resistance circuit to receive a voltage across the variable resistance circuit, wherein based on the comparison of the voltage across the variable resistance circuit and a first threshold, the first comparison circuit generates a no-load detecting signal indicative of the load status;
wherein the variable resistance circuit comprises;
a first transistor having a first terminal, a second terminal and a control terminal, wherein the first terminal is coupled to the switching mode power supply, and the second terminal is coupled to the load; and
a second transistor having a first terminal, a second terminal and a control terminal, wherein the second transistor is coupled in parallel to the first transistor;
and wherein the first transistor is ON and the second transistor is OFF under light load status, and the first transistor and the second transistor are both ON under heavy load status; and
the first comparison circuit is coupled to the first transistor to receive a drain-source voltage of the first transistor, wherein based on the comparison of the drain-source voltage of the first transistor and the first threshold, the first comparison circuit generates the no-load detecting signal.
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Accused Products
Abstract
A no-load detecting circuit and the method thereof are disclosed. The no-load detecting circuit may be applied in switching mode power supplies or other circuits. The no-load detecting circuit comprises: a variable resistance circuit coupled in series to a load of the switching mode power supply; and a first comparison circuit coupled to the variable resistance circuit to receive the voltage across the variable resistance circuit, wherein based on the comparison of the voltage across the variable resistance circuit and a first threshold, the first comparison circuit generates a no-load detecting signal indicative of the load status; wherein the equivalent resistance of the variable resistance circuit varies based on the varying of the load of the switching mode power supply.
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Citations
18 Claims
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1. A no-load detecting circuit for a switching mode power supply, comprising:
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a variable resistance circuit coupled between the switching mode power supply and a load of the switching mode power supply, wherein an equivalent resistance of the variable resistance circuit will vary depending on the status of the load of the switching mode power supply; and a first comparison circuit coupled to the variable resistance circuit to receive a voltage across the variable resistance circuit, wherein based on the comparison of the voltage across the variable resistance circuit and a first threshold, the first comparison circuit generates a no-load detecting signal indicative of the load status; wherein the variable resistance circuit comprises; a first transistor having a first terminal, a second terminal and a control terminal, wherein the first terminal is coupled to the switching mode power supply, and the second terminal is coupled to the load; and a second transistor having a first terminal, a second terminal and a control terminal, wherein the second transistor is coupled in parallel to the first transistor; and wherein the first transistor is ON and the second transistor is OFF under light load status, and the first transistor and the second transistor are both ON under heavy load status; and the first comparison circuit is coupled to the first transistor to receive a drain-source voltage of the first transistor, wherein based on the comparison of the drain-source voltage of the first transistor and the first threshold, the first comparison circuit generates the no-load detecting signal. - View Dependent Claims (2, 3, 4)
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5. A no-load detecting circuit for a switching mode power supply, comprising:
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a variable resistance circuit coupled between the switching mode power supply and a load of the switching mode power supply, wherein the variable resistance circuit comprises a first transistor having a first terminal, a second terminal and a control terminal, wherein the second terminal is coupled to the load, and wherein a drain-source voltage of the first transistor is configured to be regulated to a reference voltage; a third transistor has a first terminal, a second terminal and a control terminal, wherein the control terminal is coupled to the control terminal of the first transistor and the first terminal is coupled to the first terminal of the first transistor; a first current source coupled to the second terminal of the third transistor; and a first comparison circuit having a first input terminal, a second input terminal and an output terminal, wherein the first input terminal is coupled to the second terminal of the first transistor to receive a voltage at the second terminal of the first transistor, and the second input terminal is coupled to the second terminal of the third transistor to receive a voltage at the second terminal of the third transistor, wherein based on the comparison of the voltage at the second terminal of the first transistor and the voltage at the second terminal of the third transistor, the first comparison circuit generates a no-load detecting signal indicative of the load status.
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6. A load detecting circuit for a switching mode power supply configured to supply power to a load, wherein the switching mode power supply comprises a switching circuit, and wherein the load detecting circuit comprises:
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a no-load detecting circuit coupled to the load to detect the load status and to generate a no-load detecting signal indicative of the load status, wherein the no-load detecting circuit comprises; (i) a variable resistance circuit coupled to the load; and (ii) a first comparison circuit coupled to the variable resistance circuit to receive the voltage across the variable resistance circuit, and based on the comparison of the voltage across the variable resistance circuit and a first threshold, the first comparison circuit generates a no-load detecting signal indicative of the load status;
wherein(iii) an equivalent resistance of the variable resistance circuit is higher under heavy load status than that under light load status; and a reload detecting circuit configured to supply a current to the load when the no-load detecting signal indicates the no-load status, and generates a reload determining signal indicating whether the switching circuit is reloaded based on the comparison of the voltage across the load and a third threshold;
whereinthe switching circuit is shut down when the no-load detecting signal indicates the no-load status, and is restarted when the reload determining signal indicates the reload status. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13, 14)
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15. A load detecting method for a switching mode power supply which provides power to a load, wherein the load detecting method comprises:
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coupling a first transistor to the load; coupling a second transistor in parallel to the first transistor; comparing a drain-source voltage of the first transistor to a second threshold to determine the load status; turning ON the first transistor and the second transistor when the load is light; and turning ON the first transistor and turning OFF the second transistor when the load is heavy coupling a third transistor to the first transistor, wherein a first terminal of the first transistor and a first terminal of the third transistor are connected together, and a control terminal of the first transistor and a control terminal of the third transistor are connected together; supplying a current to a second terminal of the third transistor; regulating the drain-source voltage of the first transistor to a reference voltage after the second transistor is turned OFF; and comparing the drain-source voltage of the first transistor to a drain-source voltage of the third transistor, wherein if the drain-source voltage of the first transistor is lower than or equal to the drain-source voltage of the third transistor, a no-load status is determined. - View Dependent Claims (16, 17, 18)
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Specification