Low power dissipation power supply and controller

Details Low power dissipation power supply and controller Low power dissipation power supply and controller

2000-02-11

2001-09-25

Wong, Peter S. (Department: 2838)

Electric power conversion systems

Current conversion

With starting arrangement

C363S021100, C363S097000

Reexamination Certificate

active

06295217

ABSTRACT:

FIELD OF THE INVENTION
The invention relates generally to switched power supplies and more particularly to power supplies exhibiting low power dissipation in standby mode.
BACKGROUND
Regulated power supplies are found in virtually all electronic devices, including battery chargers, cellular telephones, computers, computer monitors, televisions, audio equipment, and video cameras. One typical power supply, the DC to DC converter, operates from a DC source, generates an alternating current as an intermediate process, and delivers direct current to a load. Switched DC converters, like linear, transformer-based power supplies, deliver a regulated output and provide isolation between input and output circuits. Unlike a linear power supply, however, the transformers in a switched DC converter operate at much higher frequencies, as high as several megahertz. This permits the use of small components, including transformers and capacitors, while still providing for complete isolation between the input and the output.
The recent demand for efficient power supplies in consumer electronic equipment has resulted in various improvements to the basic DC converter design. For example, television and computer monitors typically include power supplies capable of operating in multiple modes. A switched DC converter operating in standby mode switches at a fixed lower frequency and dissipates less power than a converter operating in a run mode. In standby mode, only the essential devices, such as microprocessors or microcontrollers, are powered.
Known designs and techniques for multi-mode power supplies are inadequate to achieve the low power dissipation requirements of modern consumer electronics. The inadequacies of current designs are magnified when the power supply must operate over a wide range of line voltages and must provide a wide range of output voltages. Modern televisions, for example, require power supplies operable from line voltages ranging from approximately 85 VRMS to 260 VRMS, and operable to deliver regulated outputs from 5 volts to 133 volts. In standby mode, power supplies will be required to dissipate less than 2 watts. Current designs cannot cost-effectively meet these voltage range requirements while achieving acceptably low power dissipation.
SUMMARY OF THE INVENTION
A power supply according to the principles of the invention operates over a wide range of line voltages and delivers a wide range of regulated outputs, while achieving lower power dissipation in standby mode than known power supplies. Low power dissipation in standby mode is achieved by disabling a start-up circuit, and by implementing variable frequency operation independent of the feedback signal. The start-up circuit provides power to the controller until feedback regulation enables. Once the start time expires, the start-up circuit is disabled so that it does not dissipate significant power. A standby mode detection circuit automatically implements the variable frequency operation. In standby mode, where power dissipation requirements can be less than two watts, disabling the start-up circuit and implementing variable frequency operation provides for significant power dissipation reduction.
A voltage controlled oscillator responsive to the rectified DC line voltage provides for the 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. Since the VCO is responsive to the line voltage, no feedback signal is required. The circuit minimizes power dissipation by reducing switching loss in the power switch and by adjusting output power without dissipating power in the feedback circuits. The standby mode detection circuit controls whether the VCO or the feedback circuit controls switching frequency.


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International Search Report for PCT/US00/08064, filed Mar. 3, 2000.

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