Load detecting circuits and the method thereof

Patent metadata

Field	Value
Publication number	US-9252766-B2
Application number	US-201213538843-A
Country	US
Kind code	B2
Filing date	Jun 29, 2012
Priority date	Jun 30, 2011
Publication date	Feb 2, 2016
Grant date	Feb 2, 2016

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.

First claim

We 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.

2. The no-load detecting circuit of claim 1 , wherein the variable resistance circuit further comprises a second comparison circuit coupled to the first transistor to receive the drain-source voltage of the first transistor, wherein the second comparison circuit is configured to compare the drain-source voltage of the first transistor with a second threshold.

3. The no-load detecting circuit of claim 1 , further comprising:
a third transistor having 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; and
a first current source coupled to the second terminal of the third transistor; wherein
the drain-source voltage of the first transistor is regulated to a reference voltage when the second transistor is turned OFF;
the first comparison circuit has 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 the 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 the voltage at the second terminal of the third transistor which serves as the first threshold, 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 the no-load detecting signal.

4. The no-load detecting circuit of claim 3 , wherein the first transistor and the second transistor are both turned ON when the drain-source voltage of the first transistor is larger than a drain-source voltage of the third transistor.

5. 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 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.

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:
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; wherein
the 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.

7. The load detecting circuit of claim 6 , wherein the reload detecting circuit comprises:
a second current source coupled to the load to supply a current to the load when the no-load detecting signal indicates the no-load status;
a fourth comparison circuit coupled to the load to receive the voltage across the load, to generate the reload determining signal indicative of the load status based on the comparison of the voltage across the load and a fourth threshold.

8. The load detecting circuit of claim 6 , wherein the no-load detecting circuit comprises:
a variable resistance circuit coupled to the load; and
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
an equivalent resistance of the variable resistance circuit is higher under heavy load status than that under light load status.

9. The load detecting circuit of claim 6 , wherein the variable resistance circuit comprises:
a first transistor coupled to the load; and
a second transistor coupled in parallel to the first transistor; and wherein
the first transistor is

Assignees

• Ren Yuancheng
• Li En
• Kuang Naixing
• Li Yike
• Chengdu Monolithic Power Sys

Inventors

• Ren Yuancheng
• Li En
• Kuang Naixing
• Li Yike

Classifications

• H02M1/00

  Details of apparatus for conversion · CPC title

• H02M1/32 Primary

  Means for protecting converters other than automatic disconnection · CPC title

• G01R31/40

  Testing power supplies (testing photovoltaic devices H02S50/10) · CPC title

• H03K17/30 Primary

  Modifications for providing a predetermined threshold before switching (shaping pulses by thresholding H03K5/08) · CPC title

• H03K17/20

  Modifications for resetting core switching units to a predetermined state · CPC title