Low power dissipation power supply and controller

• US 6,295,217 B1
• Filed: 02/11/2000
• Issued: 09/25/2001
• Est. Priority Date: 03/26/1999
• Status: Expired due to Fees

• Current Assignee: Daewoo Electronics (Government of South Korea), Sarnoff Corporation (SRI International, Inc.)
• Original Assignee: Daewoo Electronics (Government of South Korea), Sarnoff Corporation (SRI International, Inc.)
• Inventors: Yu, Joo-Dong, So, Jae-Hwan, Choi, Jae-Young, Amantea, Robert, Pletcher, Timothy Allen, Yang, Min-Sung
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): Laxton, Gary L.
• Application Number:
  US09/502,654
• Time in Patent Office: 592 Days
• Field of Search: 363/15, 363/16, 363/20, 363/21, 363/74, 363/78, 363/79, 363/80, 363/95, 363/97, 363/131, 363/49, 323/901
• US Class Current: 363/49
• CPC Class Codes: H02M 1/0032 Control circuits allowing low power mode operation, e.g. in standby mode
• CPC Class Codes: H02M 1/4258 using a single converter stage both for correction of AC input power factor and generation of a regulated and galvanically isolated DC output voltage H02M1/4241 takes precedence
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence
• CPC Class Codes: H02M 3/33561 having more than one ouput with independent control
• 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

An exemplary power supply provides low power dissipation in standby mode by disabling the start-up circuit and by implementing variable frequency operation independent of the feedback signal. A standby mode detection circuit automatically implements the variable frequency operation, and an under voltage lockout signal implements the start-up circuit disable. Once the start time expires or when feedback control enables, the start-up circuit is disabled so that it dissipates negligible power. A voltage controlled oscillator responsive to the rectified DC line voltage provides for variable frequency operation in standby mode. The frequency output of the VCO is inversely proportional to the line voltage—as line voltage increases the switching frequency decreases, which decreases the output power.

Claims

1. A switched power supply comprising:

a controller for providing feedback control when the power supply is in a run mode and for providing feedback independent control when the power supply is in a standby mode; and

a mode detection circuit operable to select at least one of the standby mode or the run mode.

2. The power supply of claim 1 further comprising:

a start-up circuit responsive to an input voltage and operable to power the controller for a programmable time;

a disable circuit operable to disable the start-up circuit when the feedback control enables; and

a variable frequency oscillator responsive to the input voltage for providing a switching signal to the controller when the power supply is in the standby mode.

3. The power supply of claim 1 wherein the power supply is one selected from the group comprising a hard switching power supply, a soft switching power supply and resonant mode power supply.

4. The power supply of claim 1 wherein the controller is a current mode controller.

5. The power supply of claim 1 wherein the controller is a voltage mode controller.

6. The power supply of claim 2 wherein the disable circuit includes:

a first switch having at least three terminals and responsive to a first signal, the first terminal and the second terminal operable to conduct when the first signal is at a threshold and the second terminal and the third terminal operable to conduct when the first signal is below the threshold;

a threshold device for maintaining the first signal at the threshold;

a power dissipating device serially connected between the input voltage and the first terminal; and

a second switch operable to turn-off the threshold device when the feedback control enables, wherein the power dissipating device is disabled.

7. The power supply of claim 6 wherein the power dissipating device is a start-up resistor, the circuit further including a capacitor serially connected to the third terminal, the start-up resistor and the capacitor providing the programmable time.

8. The power supply of claim 6 further including an energy storage device responsive to the input voltage for delivering power to the controller during a power supply start-up.

9. The power supply of claim 8 wherein the energy storage device is an inductor.

10. The power supply of claim 2 wherein the variable frequency oscillator is a voltage controlled oscillator for providing the switching signal at a frequency inversely proportional to the input voltage.

11. The power supply of claim 1 wherein the mode detection circuit includes:

a first comparator responsive to a reference voltage and a feedback signal;

a second comparator having an inverting input connected to an output of the first comparator and a noninverting input connected to a reference;

a third comparator having a noninverting input connected to the output of the first comparator and an inverting input connected to the output of the first comparator; and

an RS flip-flop having an R input and an S input, the R input coupled to an output of the second comparator and the S input coupled to an output of the third comparator.

12. An electronic device comprising a power supply according to claim 1.

13. The electronic device of claim 12 wherein the electronic device is one selected from the group comprising a television, a monitor, a computer, a phone, and an audio device.

14. A method for operating a switching power supply having a controller for controlling a switch signal, the steps comprising:

powering the controller from a start-up circuit for a programmable time;

disabling the start-up circuit when an output control is enabled;

selecting a standby mode when a required output is less than a threshold; and

varying a switching frequency in inverse proportion to the input voltage when the standby mode is selected,

wherein the step of varying the switching frequency includes the step of disabling feedback control and controlling an oscillator with an input voltage, the oscillator operable to cause the controller to set the switching frequency.