Semiconductor device for controlling switching power supply and switching power supply unit using the same

• US 20060092671A1
• Filed: 10/26/2005
• Published: 05/04/2006
• Est. Priority Date: 11/02/2004
• Status: Active Grant

• Current Assignee: Advanced Integrated Circuit Process LLC (AMTL LLC)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Yamashita, Tetsuji
• Granted Patent: US 7,285,991 B2
• Time in Patent Office: Days
• US Class Current: 363/16
• CPC Class Codes: H02M 1/0032 Control circuits allowing low power mode operation, e.g. in standby mode
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop
• 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 semiconductor device for controlling a switching power supply is provided, which can reduce power consumption at a light load of the switching power supply and improve the efficiency of the power supply. During the intermittent switching operation of a switching element, when a return signal is outputted from a light load detection circuit within the set time of a transformer reset detection time setting circuit during intermittent stop, the switching operation of the switching element is restarted in response to a transformer reset signal from the transformer reset detection circuit after the return signal is outputted. When the return signal is outputted from the light load detection circuit during the intermittent stop after the set time of the transformer reset detection time setting circuit, the switching operation of the switching element is restarted regardless of the transformer reset signal only in response to the output of the return signal.

Claims

1. A semiconductor device (51) for controlling a switching power supply, the semiconductor device being used for a switching power supply unit in which a direct-current input voltage is applied to a switching element (1) via a primary winding (103a) of a transformer (103), a direct-current voltage obtained by rectifying and smoothing an alternating current generated in a secondary winding (103b) of the transformer is controlled by a switching operation of the switching element, and power is supplied to a load, the semiconductor device controlling the switching operation of the switching element,

said semiconductor device, comprising:

a control circuit having a transformer reset detection circuit (13) for detecting a reset state of the transformer from an alternating voltage generated in a tertiary winding (103c) of the transformer and outputting a transformer reset detection signal indicating the reset state, the reset state being generated by the switching operation of the switching element,

an IV converter (29) for converting into a voltage a current value of control current indicating a change of the direct-current voltage based on the alternating current generated in the secondary winding (103b) of the transformer, and

a light load detection circuit (32) for outputting, when detecting a light load as a load condition indicating power supply to the load according to a change of an output voltage from the IV converter, a control signal for controlling an intermittent operation of switching performed by the switching element, wherein

a control electrode of the switching element is driven and the intermittent operation is controlled based on the transformer reset detection signal from the transformer reset detection circuit and the control signal from the light load detection circuit,

the light load detection circuit outputs the control signal for controlling the intermittent operation so as to stop the switching operation of the switching element when the output voltage from the IV converter is lower than a light load detection lower limit voltage for detecting the light load, and restart the switching operation of the switching element when the output voltage from the IV converter is higher than a light load detection upper limit voltage for detecting the light load,

the control circuit comprises a transformer reset detection time setting circuit (52) for setting a time of an effective period of the transformer reset detection signal from the transformer reset detection circuit, starting from stop of the switching operation in response to the control signal from the light load detection circuit, and switching on control unit for controlling timing of switching on at restart of the switching operation based on a relationship between the transformer reset detection setting time of the transformer reset detection time setting circuit and timing of the restart of the switching operation in response to the control signal from the light load detection circuit, and

the switching on control unit turns on, when the control signal indicating the restart of the switching operation is outputted from the light load detection circuit within the transformer reset detection setting time of the transformer reset detection time setting circuit, switching at the restart of the switching operation in response to the transformer reset detection signal from the transformer reset detection circuit after the control signal is outputted.

2. The semiconductor device for controlling the switching power supply according to claim 1, wherein when the control signal indicating the restart of the switching operation is outputted from the light load detection circuit after the transformer reset detection setting time of the transformer reset detection time setting circuit, the switching on control unit turns on switching at the restart of the switching operation only when the control signal is outputted.

3. The semiconductor device for controlling the switching power supply according to claim 1, wherein the transformer reset detection setting time of the transformer reset detection time setting circuit (52) is determined as an optimum time for a used load based on a drain voltage waveform of the switching operation during a stop period of the switching operation.

4. The semiconductor device for controlling the switching power supply according to claim 1, wherein a state kept after the transformer reset detection setting time of the transformer reset detection time setting circuit (52) is reset in response to an output signal for driving the control electrode of the switching element.

5. The semiconductor device for controlling the switching power supply according to claim 1, wherein the transformer reset detection time setting circuit (52) sets the transformer reset detection setting time according to a capacitance value of a capacitor and outputs timing of the transformer reset detection setting time via an RS flip-flop.

6. The semiconductor device for controlling the switching power supply according to claim 1, further comprising a time changing terminal for arbitrarily setting the transformer reset detection setting time of the transformer reset detection time setting circuit (52).

7. The semiconductor device for controlling the switching power supply according to claim 6, further comprising a capacitor for arbitrarily setting the transformer reset detection setting time of the transformer reset detection time setting circuit, the capacitor being connected between the time changing terminal and a ground.

8. The semiconductor device for controlling the switching power supply according to claim 1, wherein

the switching element and the control circuit are integrated on the same semiconductor substrate, and

the semiconductor device comprises, as external connection terminals on the semiconductor substrate,

at least a switching element input terminal for inputting the input voltage to the switching element via the primary winding of the transformer,

a switching element output terminal for outputting a switching current obtained by the switching operation of the switching element,

a power supply terminal for supplying a direct-current voltage to the control circuit in response to the switching operation of the switching element according to a current generated in the tertiary winding of the transformer,

a control terminal for inputting a control signal for controlling an intermittent operation of switching performed by the switching element, and

a transformer reset detection terminal for applying a signal for transformer reset detection to the transformer reset detection circuit.

9. A switching power supply unit, wherein a direct-current voltage obtained by rectifying and smoothing an alternating current generated in a secondary winding of a transformer is controlled and power is supplied to a load by applying a direct-current input voltage to a switching element via a primary winding of the transformer and controlling the switching element by means of the semiconductor device for controlling the switching power supply according to claim 1 to perform a switching operation.