Synchronous rectification switching regulator, control circuit for synchronous rectification switching regulator, and control method for same

• US 20080080219A1
• Filed: 09/27/2007
• Published: 04/03/2008
• Est. Priority Date: 09/29/2006
• Status: Active Grant

• Current Assignee: RICOH Electronic Devices Co., Ltd. (Nisshinbo Holdings Incorporated)
• Original Assignee: Ricoh Company Limited
• Inventors: Sohma, Shohtaroh
• Granted Patent: US 7,795,849 B2
• Time in Patent Office: Days
• US Class Current: 363/89
• CPC Class Codes: H02M 3/1588 comprising at least one synchronous rectifier element H02M3/1582, H02M3/1584 take precedence
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A control circuit for a synchronous rectification switching regulator including an output terminal, a switching transistor, an inductor, and a synchronous rectification transistor has a control part configured to control switching of the switching transistor to charge the inductor to and set a voltage output from the output terminal to a predetermined voltage, which causes the synchronous rectification transistor to switch reversely to the switching transistor and discharge the inductor, and backflow prevention part configured to block a current flowing in the synchronous rectification transistor to prevent a backflow current that flows in a direction from the output terminal to the synchronous rectification transistor. The backflow prevention part detects a forward current and regulates timing to block the current flowing in the synchronous rectification transistor and to regulate a time period from blocking the current flowing in the synchronous rectification transistor to determining that the forward current is zero.

Claims

1. A control circuit for a synchronous rectification switching regulator including:

an output terminal configured to output a constant voltage to a load connected thereto;

a switching transistor configured to perform switching according to a control signal;

an inductor configured to be charged with an input voltage by the switching of the switching transistor; and

a synchronous rectification transistor configured to perform switching according to a control signal to discharge the inductor,

the control circuit comprising;

a control part configured to control the switching of the switching transistor to set the voltage output from the output terminal to a predetermined voltage and cause the synchronous rectification transistor to switch reversely to the switching of the switching transistor; and

a backflow prevention part configured to block a current flowing in the synchronous rectification transistor to prevent a backflow current flowing in a direction from the output terminal to the synchronous rectification transistor,

wherein the backflow prevention part detects a forward current that flows when the synchronous rectification transistor discharges the inductor and regulates timing to block the current flowing in the synchronous rectification transistor to prevent an occurrence of the backflow current and to regulate a time period from blocking the current flowing in the synchronous rectification transistor to determining that the forward current is zero.

2. The control circuit of claim 1, wherein the backflow prevention part comprises a resistance for detecting an inductor current flowing in the inductor, the resistance configured to convert the inductor current into a voltage;

and

the forward current and the backflow current are detected based on voltages at both ends of the resistance.

3. The control circuit of claim 2, wherein the backflow prevention part further comprises:

a backflow prevention transistor connected in series with the synchronous rectification transistor, configured to switch according to a control signal input to a control electrode thereof;

a backflow detection part configured to turn off the backflow prevention transistor to block the current flowing in the synchronous rectification transistor when detecting an indication or an occurrence of the backflow current based on the voltages at both ends of the resistance; and

a regulation part configured to detect the forward current based on the voltages at both ends of the resistance and control the backflow detection part to set the timing to turn off the backflow prevention transistor and set the time period from blocking the current flowing in the synchronous rectification transistor to determining that the forward current is zero to a predetermined time.

4. The control circuit of claim 2, wherein the backflow prevention part further comprises:

a backflow detection part configured to turn off the synchronous rectification transistor to block the current flowing therein when detecting an indication or an occurrence of the backflow current based on the voltages at both ends of the resistance; and

a regulation part configured to detect the forward current based on the voltages at both ends of the resistance and control the backflow detection part to set the timing to turn off the synchronous rectification transistor and set the time period from blocking the current flowing in the synchronous rectification transistor to determining that the forward current is zero to a predetermined time.

5. The control circuit of claim 1, wherein the backflow prevention part comprises:

a backflow prevention transistor connected in series with the synchronous rectification transistor, configured to perform switching according to a control signal input to a control electrode thereof;

a backflow detection part configured to turn off the backflow prevention transistor to block the current flowing in the synchronous rectification transistor when detecting an indication or an occurrence of the backflow current based on voltages at both ends of the backflow prevention transistor; and

a regulation part configured to detect the forward current based on the voltages at both ends of the backflow prevention transistor and control the backflow detection part to set the timing to turn off the backflow prevention transistor and set the time period from blocking the current flowing in the synchronous rectification transistor to determining that the forward current is zero to a predetermined time.

6. The control circuit of claim 1, wherein the backflow prevention part comprises:

a backflow detection part configured to turn off the synchronous rectification transistor to block the current flowing in the synchronous rectification transistor when detecting an indication or an occurrence of the backflow current based on voltages at both ends of the synchronous rectification transistor; and

a regulation part configured to detect the forward current based on the voltages at both ends of the synchronous rectification transistor and control the backflow detection part to set the timing to turn off the synchronous rectification transistor and set the time period from blocking the current flowing in the synchronous rectification transistor to determining that the forward current is zero to a predetermined time.

7. The control circuit of claim 3, wherein the regulation part is configured to set the predetermined time.

8. The control circuit of claim 3, wherein the backflow detection part further comprises:

a voltage comparison circuit configured to compare the voltages at both ends of the resistance; and

a drive control circuit configured to control the switching of the backflow prevention transistor according to a voltage comparison result produced by the voltage comparison circuit,

wherein the control part controls an offset voltage of the voltage comparison circuit to regulate the timing to turn off the synchronous rectification transistor.

9. The control circuit of claim 5, wherein the backflow detection part further comprises:

a voltage comparison circuit configured to compare the voltages at both ends of the backflow prevention transistor; and

a drive control circuit configured to control the backflow prevention transistor to switch-according to a voltage comparison result produced by the voltage comparison circuit,

wherein the control part controls an offset voltage of the voltage comparison circuit to regulate the timing to turn off the synchronous rectification transistor.

10. The control circuit of claim 6, wherein the backflow detection part comprises:

a voltage comparison circuit configured to compare the voltages at both ends of the synchronous rectification transistor; and

a drive control circuit configured to control the synchronous rectification transistor to switch according to a voltage comparison result produced by the voltage comparison circuit,

wherein the control part controls the offset voltage of the voltage comparison circuit to regulate the timing to turn off the synchronous rectification transistor.

11. The control circuit of claim 5 wherein the backflow detection part comprises:

a voltage comparison circuit configured to compare the voltages at both ends of the backflow prevention transistor and to output a signal indicating a result of the voltage comparison;

a delay circuit configured to transmit the signal from the voltage comparison circuit after a delay time;

a drive control circuit configured to control the backflow prevention transistor to switch according to the signal transmitted via the delay circuit,

wherein the control part controls the delay time of the delay circuit to regulate the timing to turn off the synchronous rectification transistor.

12. The control circuit of claim 6 wherein the backflow detection part comprises:

a voltage comparison circuit configured to compare the voltages at both ends of the synchronous rectification transistor and to output a signal indicating a result of the voltage comparison;

a delay circuit configured to transmit the signal output from the voltage comparison circuit after a delay time; and

a drive control circuit configured to control the synchronous rectification transistor to switch according to the signal transmitted via the delay circuit,

wherein the control part controls the delay time to regulate the timing to turn off the synchronous rectification transistor.

13. A synchronous rectification switching regulator, comprising:

an output terminal configured to output a constant voltage to a load connected thereto;

a switching transistor configured to perform switching according to a control signal;

an inductor configured to be charged with an input voltage by the switching of the switching transistor;

a synchronous rectification transistor configured to perform switching according to a control signal to discharge the inductor;

a control part configured to control the switching of the switching transistor to set the voltage output from the output terminal to a predetermined voltage and cause the synchronous rectification transistor to switch reversely to the switching transistor; and

a backflow prevention part configured to block a current flowing in the synchronous rectification transistor to prevent a backflow current flowing in a direction from the output terminal to the synchronous rectification transistor,

wherein the backflow prevention part detects a forward current that flows when the synchronous rectification transistor discharges the inductor and regulates timing to block the current flowing in the synchronous rectification transistor to prevent an occurrence of the backflow current and regulate a time period from blocking the current flowing in the synchronous rectification transistor to determining that the forward current is zero.

14. The synchronous rectification switching regulator of claim 13, wherein:

the backflow prevention part comprises a resistance for detecting an inductor current flowing in the inductor, configured to convert the inductor current into a voltage; and

the forward current and the backflow current are detected based on voltages at both ends of the resistance.

15. The synchronous rectification switching regulator of claim 14, wherein the backflow prevention part further comprises:

a backflow prevention transistor connected in series with the synchronous rectification transistor, configured to switch according to a control signal input to a control electrode thereof;

a backflow detection part configured to turn off the backflow prevention transistor to block the current flowing in the synchronous rectification transistor when detecting an indication or an occurrence of the backflow current based on the voltages at both ends of the resistance; and

a regulation part configured to detect the forward current based on the voltages at both ends of the resistance and control the backflow detection part to set the timing to turn off the backflow prevention transistor and set the time period from blocking the current flowing in the synchronous rectification transistor to determining that the forward current is zero to a predetermined time.

16. The synchronous rectification switching regulator of claim 14, wherein the backflow prevention part further comprises:

a backflow detection part configured to turn off the synchronous rectification transistor to block the current flowing therein when detecting an indication or an occurrence of the backflow current based on the voltages at both ends of the resistance; and

a regulation part configured to detect the forward current based on the voltages at both ends of the resistance and control the backflow detection part to set the timing to turn off the synchronous rectification transistor and set the time period from blocking the current flowing in the synchronous rectification transistor to determining that the forward current is zero to a predetermined time.

17. The synchronous rectification switching regulator of claim 13, wherein the backflow prevention part comprises:

a backflow prevention transistor connected in series with the synchronous rectification transistor, configured to perform switching according to a control signal input to a control electrode thereof;

a backflow detection part configured to turn off the backflow prevention transistor to block the current flowing in the synchronous rectification transistor when detecting an indication or an occurrence of the backflow current based on voltages at both ends of the backflow prevention transistor; and

a regulation part configured to detect the forward current based on the voltages at both ends of the backflow prevention transistor and control the backflow detection part to set the timing to turn off the backflow prevention transistor and set the time period from blocking the current flowing in the synchronous rectification transistor to determining that the forward current is zero to a predetermined time.

18. The synchronous rectification switching regulator of claim 13, wherein the backflow prevention part comprises:

a backflow detection part configured to turn off the synchronous rectification transistor to block the current flowing in the synchronous rectification transistor when detecting an indication or an occurrence of the backflow current based on voltages at both ends of the synchronous rectification transistor; and

a regulation part configured to detect the forward current based on the voltages at both ends of the synchronous rectification transistor and control the backflow detection part to set the timing to turn off the synchronous rectification transistor and set the time period from blocking the current flowing in the synchronous rectification transistor to determining that the forward current is zero to a predetermined time.

19. The synchronous rectification switching regulator of claim 15, wherein the regulation part is configured to set the predetermined time.

20. A control method of controlling a synchronous rectification switching regulator having

an output terminal configured to output a constant voltage to a load connected thereto,

a switching transistor configured to perform switching according to a control signal,

an inductor configured to be charged with an input voltage by the switching of the switching transistor, and

a synchronous rectification transistor configured to perform switching according to a control signal to discharge the inductor;

the control method, comprising;

controlling the switching of the switching transistor to set the voltage output from the output terminal to a predetermined voltage and causing the synchronous rectification transistor to switch reversely to the switching transistor;

detecting a forward current that flows when the synchronous rectification transistor discharges the inductor;

blocking a current flowing in the synchronous rectification transistor to prevent a backflow current flowing in a direction from the output terminal to the synchronous rectification transistor;

determining that the forward current is zero; and

regulating timing to block the current flowing in the synchronous rectification transistor to regulate a time period from blocking the current flowing in the synchronous rectification transistor to determining that the forward current is zero.