Control apparatus for inhibiting synchronous-rectifier switching elements at low output current in a voltage transforming apparatus

• US 7,773,399 B2
• Filed: 01/29/2007
• Issued: 08/10/2010
• Est. Priority Date: 01/27/2006
• Status: Active Grant

• Current Assignee: DENSO Corporation, Nippon Soken, Inc.
• Original Assignee: DENSO Corporation, Nippon Soken, Inc.
• Inventors: Hayashi, Yuji, Yamashita, Tsuyoshi, Nakamura, Kimikazu
• Primary Examiner(s): BEHM, HARRY RAYMOND
• Application Number:
  US11/699,075
• Publication Number:
  US 20070177409A1
• Time in Patent Office: 1,289 Days
• Field of Search: 363/127, 363/21.06, 363/21.14, 363 79- 81, 363/17, 363/98, 363/132
• US Class Current: 363/127
• CPC Class Codes: H02M 3/33592 having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer
• 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

The control apparatus for controlling a voltage transforming apparatus having a transformer, power switching elements disposed in a primary side, and synchronous-rectifying switching elements disposed in a secondary side includes a judging circuit making a judgment as to whether or not an output current of the voltage transforming apparatus is smaller than a specified current on the basis of a primary-side current of the transformer and an inhibition circuit inhibiting the synchronous-rectifying switching elements from performing their synchronous-rectifying control operation when the judging circuit judges that the output current is smaller than the specified current. The judging circuit makes the judgment on the basis of the primary-side current flowing through the primary coil of the transformer immediately before the power switching elements are turned off.

Claims

1. A control apparatus for controlling a voltage transforming apparatus including a transformer, power switching elements provided in a primary side of said transformer and performing on-operation and off-operation to invert a DC input voltage to an AC voltage, a synchronous-rectifying switching elements provided in a secondary side of said transformer and performing synchronous-rectifying control operation in synchronization with said power switching elements in order to rectify said AC voltage transformed by said transformer into a DC output voltage, and a smoothing circuit smoothing said DC output voltage, said control apparatus comprising:

a driver circuit outputting first and second drive signals to said power switching elements, said power switching elements performing said on-operation while receiving said first drive signal, and performing said off-operation while receiving said second drive signal;

a judging circuit making a judgment as to whether or not an output current of said voltage transforming apparatus is smaller than a specified current on the basis of a primary-side current flowing through a primary coil of said transformer before said second drive signal is outputted from said driver circuit in order to prevent said judging circuit from making said judgment on the basis of said primary-side current while said driver circuit outputs said second drive signal; and

an inhibition circuit inhibiting said synchronous-rectifying switching elements from performing said synchronous-rectifying control operation when said judging circuit judges that said output current is smaller than said specified current.

2. The control apparatus according to claim 1, further comprising an error signal generating circuit generating an error signal indicative of a difference between a detection value of said DC output voltage and a reference voltage, and a PWM modulating circuit generating a PWM signal having a duty ratio depending on said error signal, and wherein the driver circuit generates, through power conversion of said PWM signal, said drive signals to said power switching elements and said judging circuit makes said judgment at a timing in synchronization with said PWM signal appearing upstream of said driver circuit.

3. The control apparatus according to claim 2, wherein said judging circuit makes said judgment, while compensating for at least one of effect of variation of said duty ratio of said power switching elements, effect of variation of said DC output voltage, and effect of variation of said DC input voltage on a relationship between said primary-side current and said output current of said voltage transforming apparatus.

4. The control apparatus according to claim 1, further comprising an error signal generating circuit generating an error signal indicative of a difference between a detection value of said DC output voltage and a reference voltage, a PWM modulating circuit generating a PWM signal having a duty ratio depending on said error signal, and wherein the driver circuit generates, through power conversion of said PWM signal, said drive signals to said power switching elements, and said judging circuit makes said judgment at a timing in synchronization with said drive signals being outputted from said driver circuit.

5. The control apparatus according to claim 3, wherein said judging circuit makes said judgment, while compensating for at least one of effect of variation of said duty ratio of said power switching elements, effect of variation of said DC output voltage, and effect of variation of said DC input voltage on a relationship between said primary-side current and said output current of said voltage transforming apparatus.

6. A method of controlling a voltage transforming apparatus including a transformer, power switching elements provided in a primary side of said transformer and performing on-operation and off-operation to invert a DC input voltage to an AC voltage, a synchronous-rectifying switching elements provided in a secondary side of said transformer and performing synchronous-rectifying control operation in synchronization with said power switching elements in order to rectify said AC voltage transformed by said transformer into a DC output voltage, and a smoothing circuit smoothing said DC output voltage, said method comprising:

outputting, from a driver circuit, first and second drive signals to said power switching elements, said power switching elements performing said on-operation while receiving said first drive signal, and performing said off-operation while receiving said second drive signal;

making a judgment as to whether or not an output current of said voltage transforming apparatus is smaller than a specified current on the basis of a primary-side current flowing through a primary coil of said transformer before said second drive signal is outputted from said driver circuit in order to prevent said judging circuit from making said judgment on the basis of said primary-side current while said driver circuit outputs said second drive signal; and

inhibiting said synchronous-rectifying switching elements from performing said synchronous-rectifying control operation when said judgment is that said output current is smaller than said specified current.

7. The method according to claim 6, further comprising generating an error signal indicative of a difference between a detection value of said DC output voltage and a reference voltage, generating a PWM signal having a duty ratio depending on said error signal, and generating, through power conversion of said PWM signal, said drive signals to said power switching elements, said judgment being made at a timing in synchronization with said PWM signal appearing upstream of a position where the drive signals are generated.

8. The method according to claim 6, further comprising generating an error signal indicative of a difference between a detection value of said DC output voltage and a reference voltage, generating a PWM signal having a duty ratio depending on said error signal, and generating, through power conversion of said PWM signal, said drive signals to said power switching elements, said judgment being made at a timing in synchronization with said drive signals being output.

9. The method according to claim 7, wherein said judgment is made while compensating for at least one of effect of variation of said duty ratio of said power switching elements, effect of variation of said DC output voltage, and effect of variation of said DC input voltage on a relationship between said primary-side current and said output current of said voltage transforming apparatus.

10. The method according to claim 8, wherein said judgment is made while compensating for at least one of effect of variation of said duty ratio of said power switching elements, effect of variation of said DC output voltage, and effect of variation of said DC input voltage on a relationship between said primary-side current and said output current of said voltage transforming apparatus.