Switching power supply device and the semiconductor integrated circuit for power supply control

• US 20040136209A1
• Filed: 12/05/2003
• Published: 07/15/2004
• Est. Priority Date: 01/09/2003
• Status: Active Grant

• Current Assignee: Renesas Technology Corporation (Renesas Electronics Corporation)
• Original Assignee: Renesas Technology Corporation (Renesas Electronics Corporation)
• Inventors: Kudo, Ryotaro, Hosokawa, Kyoichi, Yoshida, Shinichi, Onda, Kenichi, Uehara, Yoichi
• Granted Patent: US 7,158,392 B2
• Time in Patent Office: Days
• US Class Current: 363/24
• CPC Class Codes: H02M 1/0048 Circuits or arrangements for reducing losses using snubbers H02M1/34
• 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: H02M 3/3376 with automatic control of output voltage or current
• 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

It is aimed at decreasing losses not only in a synchronous rectifier circuit provided at a secondary side of a DC-DC converter, but also in a full-bridge switching circuit provided at a primary side thereof. The DC-DC converter comprises a transformer for voltage conversion, a synchronous rectifier circuit at the secondary side, and a full-bridge switching circuit at the primary side. The DC-DC converter performs synchronous rectifier control which uses switch transistors to change paths of currents flowing through the secondary coil in synchronization with switching operations at the primary side. The DC-DC converter detects currents flowing through a load at the secondary side, primary-side currents varying with the load currents, or primary-side input voltages to dynamically control off-timings of a synchronous rectification transistor at the secondary side. In addition, the DC-DC converter detects primary-side input voltages and currents flowing through the secondary-side load to dynamically control on-timings of a transistor in the primary-side switching circuit.

Claims

1. A semiconductor integrated circuit for power supply control for performing switching control of a switching power supply device which switches currents flowing through a primary coil of a transformer for voltage conversion to drive the primary coil with alternate currents and rectifies currents flowing through a secondary coil of the transformer to output DC voltages,

wherein the semiconductor integrated circuit generates and outputs a signal for dynamically controlling off-timings of a transistor for synchronous rectification at the secondary coil in accordance with either an input voltage of the primary coil or a load current of the secondary coil, or both of the input voltage of the primary coil and the load current of the secondary coil.

2. The semiconductor integrated circuit for power supply control according to claim 1,

wherein the semiconductor integrated circuit generates and outputs a signal to dynamically control on-timings of a switching element for switching currents flowing through the primary coil in accordance with input voltages of the primary coil.

3. The semiconductor integrated circuit for power supply control according to claim 1,

wherein the semiconductor integrated circuit generates and outputs a signal to dynamically control on-timings of a switching element for switching currents flowing through the primary coil in accordance with load currents at the secondary side.

4. The semiconductor integrated circuit for power supply control according to claim 1,

wherein the semiconductor integrated circuit generates and outputs a signal to dynamically control on-timings of a switching element for switching currents flowing through the primary coil in accordance with input voltages of the primary coil and load currents at the secondary side.

5. The semiconductor integrated circuit for power supply control according to claim 1,

wherein the semiconductor integrated circuit generates and outputs a control signal by turning on or off a first synchronous rectification transistor and a second synchronous rectification transistor,

the first synchronous rectification transistor being connected between one terminal of the secondary coil and a reference potential point and turned on or off in synchronization with a switching operation for switching currents flowing through the primary coil, and

the second synchronous rectification transistor being connected between the other terminal of the secondary coil and the reference potential point and turned on or off in synchronization with the switching operation at the primary side.

6. The semiconductor integrated circuit for power supply control according to claim 5, comprising:

a first control signal generation circuit to generate a control signal used for switching currents flowing through the primary coil;

a second control signal generation circuit to generate control signals for the first and second synchronous rectification transistors at the secondary side based on a signal generated by the first control signal generation circuit;

a variable delay circuit capable of supplying any delay to control signals generated by the first and second control signal generation circuits;

an external terminal to input setup information for specifying a delay amount supplied by the variable delay circuit;

a delay amount control circuit to generate, based on setup information from the external terminal, a signal for controlling a delay amount in the variable delay circuit; and

a nullification means for nullifying delay amount control by the delay amount control circuit,

wherein the nullification means nullifies operations of the delay amount control circuit in accordance with a state of the external terminal.

7. The semiconductor integrated circuit for power supply control according to claim 6, comprising:

a detection means for detecting whether or not the load current goes below a specified value,

wherein, when the load current goes below a specified value, the variable delay circuit is changed to supply no delay to off-timings of the control signal for the first and second synchronous rectification transistors.

8. The semiconductor integrated circuit for power supply control according to claim 1, comprising:

a voltage monitoring means for detecting a level of the primary input voltage and, when the input voltage reaches a specified level, stops supplying power to an internal circuit,

wherein an input terminal for voltages monitored by the voltage monitoring means is also used as an input terminal for voltages of the primary coil which is monitored to control on-timings of the switching element for switching currents flowing through the primary coil.

9. The semiconductor integrated circuit for power supply control according to claim 6,

wherein information about load currents input to the first control signal generation circuit and information about load currents input to the delay amount control circuit are input from the same external terminal.

11. A switching power supply device comprising:

the semiconductor integrated circuit for power supply control according to any of claims 1 through 10;

a transformer for voltage conversion;

a switching circuit which switches currents flowing through the primary coil of the transformer for voltage conversion to drive the primary coil with alternate currents;

a rectifier circuit including a synchronous rectification transistor and rectifies currents flowing through a secondary coil to output DC voltages, the synchronous rectification transistor being connected between one terminal of the secondary coil of the transformer for voltage conversion and a reference potential terminal and turned on or off in synchronization with switching operations of the switching circuit; and

a capacitor element for smoothing voltages rectified by the rectifier circuit,

wherein an input voltage to the primary coil is divided by resistors and is supplied to the semiconductor integrated circuit for power supply control.

10. A semiconductor integrated circuit for power supply control for performing switching control of a switching power supply device which switches currents flowing through a primary coil of a transformer for voltage conversion to drive the primary coil with alternate currents and rectifies currents flowing through a secondary coil of the transformer to output DC voltages,

wherein the semiconductor integrated circuit is configured to be able to set any detection criterion level for a circuit to generate a signal which detects a voltage between terminals of a switching element in a circuit for switching currents flowing through the primary coil and controls on-timings.