Switched-mode power supply supporting burst-mode operation

• US 20030042879A1
• Filed: 06/05/2002
• Published: 03/06/2003
• Est. Priority Date: 08/28/2001
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Fairchild Korea Semiconductor Limited (ON Semiconductor Corporation)
• Inventors: Joo, Yong-Jin, Huh, Dong-Young
• Granted Patent: US 7,054,169 B2
• Time in Patent Office: Days
• US Class Current: 323/282
• CPC Class Codes: H02M 1/0032 Control circuits allowing low power mode operation, e.g. in standby mode
• CPC Class Codes: H02M 1/0041 Control circuits in which a clock signal is selectively enabled or disabled
• 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 switched-mode power supply (SMPS) that operates in a burst mode when an electronic device that receives power from the SMPS demands a low level of power as when in a stand-by mode or cut-off mode. The SMPS contains a first power supply unit for receiving a power and rectifying it, and, according to a level of an output for the load, distinguishing between a normal mode and a burst mode to perform switching according to a timing corresponding to the normal mode and the burst mode to supply a first power. The SMPS also contains an output power supply unit for receiving the first power from the first power supply unit according to a winding ratio of a coil to generate a power for driving the load.

Claims

1. A switched-mode power supply supporting burst-mode operation, in which the power supply provides an output power to a load, the power supply comprising:

a first power supply unit for receiving an input power and rectifying the power, and, according to a level of an output for the load, distinguishing between a normal mode and a burst mode to perform switching according to a timing corresponding to one of the normal mode or the burst mode to supply a first power; and

an output power supply unit for receiving the first power from the first power supply unit according to a winding ratio of a coil to generate an output power for driving the load.

2. The power supply of claim 1, wherein the first power supply unit comprises:

a first power converter for receiving the input power, rectifying the input power, then outputting a resulting power;

an output power sensing unit for sensing the output power that is output to the load from the output power supply unit and outputting a corresponding signal;

a mode determination unit for determining when conditions for operation in a burst mode are satisfied, the mode determination unit performing this operation using a level of the signal output by the output power sensing unit, and the mode determination unit generating and outputting a corresponding control signal;

a switching controller for outputting a signal to control timing of the switch according to the signal output from the output power sensing unit and a signal output from the mode determination unit; and

a switching unit for switching On and Off according to the operation of the switching controller to enable transmission of power converted by the first power converter to the output power supply unit.

3. The power supply of claim 2, wherein the output power sensing unit comprises a phototransistor for receiving as a light signal and through a base thereof, an output power that is sensed and undergoes feedback from the output power supply unit.

4. The power supply of claim 2, wherein the mode determination unit comprises:

a first comparator for determining if conditions for burst-mode operation are satisfied, and outputting a corresponding sensing signal, the first comparator performing this operation using the signal sensed in the output power sensing unit;

a switch Off detector for detecting a basic Off position of the switching unit;

a burst signal regulating unit for receiving the burst mode sensing signal output from the first comparator and adjusting the burst mode sensing signal so that it corresponds to a signal output from the switch Off detector, after which the burst signal regulating unit outputs the burst mode sensing signal; and

a burst controller for receiving the signal output from the burst signal regulating unit and outputting a signal to the switching controller to enable control into the burst mode when the burst mode sensing signal is maintained for a predetermined duration.

5. The power supply of claim 4, wherein the first comparator receives the signal sensed in the output power sensing unit through a non-inverting input terminal, and receives through an inverting input terminal a first reference voltage having a second reference value and a third reference value, which is smaller than the second reference value, thereby performing a hysteresis operation.

6. The power supply of claim 5, wherein a voltage value of the first reference voltage becomes the second reference value when the output signal of the first comparator converts to On, and the voltage value of the first reference voltage becomes the third reference value when the output signal of the first comparator converts to Off.

7. The power supply of claim 4, wherein the burst signal regulating unit comprises:

a first AND gate for performing a logical AND operation of the output signal of the first comparator and the output signal of the switch Off detector, and outputting a resulting signal;

an inverter for inverting the output signal of the first comparator and outputting a resulting signal;

a second AND gate for performing a logical AND operation of the output signal of the inverter and the output signal of the switch Off detector, and outputting a resulting signal;

a first switch that opens and closes according to the output signal of the first AND gate to apply a predetermined power to the burst controller; and

a second switch that opens and closes according to the output signal of the second AND gate to ground the burst controller.

8. The power supply of claim 4, wherein the burst controller comprises:

a capacitor that is charged and discharged according to the output signal of the burst signal regulating unit; and

a second comparator, receiving through a non-inverting input terminal the output signal of the burst signal regulating unit through the capacitor, and comparing this signal with a second reference voltage to generate and output a control signal, the second reference voltage being of a predetermined value having a fourth reference value and a fifth reference value, and which performs a hysteresis operation, and the second comparator receiving the second reference voltage through an inverting terminal.

9. The power supply of claim 8, wherein a voltage value of the second reference voltage becomes the fourth reference value when the output signal of the first comparator converts to On, and the voltage value of the second reference voltage becomes the fifth reference value when the output signal of the second comparator converts to Off.

10. The power supply of claim 2, wherein the mode determination unit comprises:

a variable comparator for determining if conditions for burst-mode operation are satisfied, and outputting a corresponding sensing signal, the variable comparator performing this operation using the signal sensed in the output power sensing unit;

a switch Off detector for detecting a basic Off position of the switching transistor;

a burst signal regulating unit for receiving the burst mode sensing signal output from the variable comparator and adjusting the burst mode sensing signal so that it corresponds to a signal output from the switch Off detector, after which the burst signal regulating unit outputs the burst mode sensing signal; and

a flip-flop for latching a signal corresponding to the signal output from the burst signal regulating unit, then outputting this signal to the switching controller.

11. The power supply of claim 10, wherein the variable comparator receives the signal sensed in the output power sensing unit through a non-inverting input terminal, and receives through an inverting input terminal a first reference voltage having a second reference value and a third reference value, which is smaller than the second reference value, thereby performing a hysteresis operation.

12. The power supply of claim 11, wherein a voltage value of the first reference voltage becomes the second reference value when the output signal of the variable comparator converts to On, and the voltage value of the first reference voltage becomes the third reference value when the output signal of the variable comparator converts to Off.

13. The power supply of claim 10, wherein the burst signal regulating unit comprises:

a first AND gate for performing a logical AND operation of the output signal of the variable comparator and the output signal of the switch Off detector, and outputting a resulting signal;

an inverter for inverting the output signal of the variable comparator and outputting a resulting signal to a set terminal of the flip-flop; and

a second AND gate for performing a logical AND operation of the output signal of the inverter and the output signal of the switch Off detector, and outputting a resulting signal to a reset terminal of the flip-flop.

14. The power supply of claim 2, wherein the switching controller comprises:

a comparator for comparing the signal sensed in the output power sensing unit with a pre-installed first reference value, and outputting a corresponding signal;

a flip-flop, which is reset according to the output signal of the comparator;

an OR gate for outputting a signal according to a signal output from the flip-flop and a burst control signal output from the mode determination unit; and

a transistor for opening and closing the switching unit according to the signal output from the OR gate.

15. A method of regulating the efficiency and output power of a switched-mode power supply, the method comprising:

receiving an input power and rectifying said input power;

distinguishing between a normal mode and a burst mode; and

controlling a switch at different time intervals to relay power through a transformer to an output power supply unit to drive a load.

16. The method of claim 15, wherein said receiving and rectifying of an input power is accomplished using a power converter.

17. The method of claim 16, further comprising:

providing a resulting power to an output power sensing unit;

sensing the power output to the load; and

transmitting a signal to a mode determination unit indicative of said power output.

18. The method of claim 17, wherein transmitting the signal to the mode determination unit comprises transmitting an optical signal.

19. The method of claim 15, wherein said distinguishing between normal mode and burst mode comprises the mode determination unit receiving a signal from the output power sensing unit corresponding to the amount of the load at the output of the power supply.

20. The method of claim 19, wherein said mode determination unit comprising a comparator receives a signal from the said output power sensing unit, thereby comparing the signal to a predetermined voltage and sending a HIGH or LOW signal signifying normal mode or burst mode.

21. The method of claim 15, wherein said controlling a switch at different time intervals comprises logic gates receiving a signal from a Switch Off detector and the comparator of said mode determination unit.

22. The method of claim 21, further comprising relaying a signal to a switching controller.

23. The method of claim 22, comprising a comparator receiving as input, the output of one of the said logic devices as determined by an accompanying switch with each logic device and a predetermined voltage, and outputting a HIGH or LOW signal to the switching controller.

24. The method of claim 22, comprising a flip-flop receiving as input, the output of the normal mode logic to the input and the output of the burst mode logic to the reset, and outputting the input or a LOW state as determined by the mode determination unit to the switching controller.

25. The method of claim 24, wherein comprising logic gates include two AND gates and one inverter sending opposite signals (HIGH and LOW) to provide control signals to said comparator and said flip-flop.

26. The method of claim 15, further comprising a switching controller receiving as input;

a clock signal, a signal from a phototransistor of the output power sensing unit, and a signal relayed from the mode determination unit, and outputting a voltage controlling a switch which transfers power through a transformer to the load.

27. A power supply for providing an output power, the power supply comprising:

an input unit supplying a first power, the unit distinguishing between a normal mode and a burst mode to perform switching according to the normal mode or the burst mode according to a level of the output power; and

an output unit for receiving said first power according to a winding ratio of a coil and for generating the output power.