Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2002-09-23
2004-08-24
Patel, Rajnikant B. (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C323S235000, C363S097000
Reexamination Certificate
active
06781357
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to power supplies and, more specifically, the present invention relates to a switched mode power supply.
2. Background Information
All electronic devices use power to operate. A form of power supply that is highly efficient and at the same time provides acceptable output regulation to supply power to electronic devices or other loads is the switched-mode power supply. In many electronic device applications, especially the low power off-line adapter/charger market, during the normal operating load range of the power supply an approximately constant output voltage is required below an output current threshold. The current output is generally regulated below an output voltage in this region of approximately constant output voltage, hereafter referred to as the output voltage threshold.
In known switched mode power supplies without secondary current sensing circuitry, minimizing the variation of the output current at the output voltage threshold is performed with complex control schemes. Typically, these schemes include the measurement of input voltage, output diode conduction time and peak primary current limit. Some or all of this measured information is then used to control the regulator in order to reduce the variation of the output current at the output voltage threshold.
SUMMARY OF THE INVENTION
A power supply that maintains an approximately constant load current with line voltage below the output voltage threshold is disclosed. In one embodiment, a regulation circuit includes a semiconductor switch and current sense circuitry to sense the current in the semiconductor switch. The current sense circuitry has a current limit threshold. The regulation circuit current limit threshold is varied from a first level to a second level during the time when the semiconductor switch is on. In one embodiment, the regulation circuit is used in a power supply having an output characteristic having an approximately constant output voltage below an output current threshold and an approximately constant output current below an output voltage threshold. In another embodiment, a power supply is described, which includes a power supply input and a power supply output and that maintains an approximately constant load current with line voltage below the output voltage threshold. In one embodiment, the power supply has an output characteristic having an approximately constant output voltage below an output current threshold and an approximately constant output current below an output voltage threshold. A regulation circuit is coupled between the power supply input and the power supply output. The regulation circuit includes a semiconductor switch and current sense circuitry to sense the current in the semiconductor switch. The current sense circuitry has a current limit threshold. The regulation circuit current limit threshold is varied from a first level to a second level during the time when the semiconductor switch is on. In another aspect, the current limit threshold being reached coincides with the power supply output characteristic transitioning from providing an approximately constant output voltage to supplying an approximately constant output current. In yet another aspect, the semiconductor switch is a MOSFET. Additional features and benefits of the present invention will become apparent from the detailed description and figures set forth below.
REFERENCES:
patent: 4392103 (1983-07-01), O'Sullivan et al.
patent: 5680034 (1997-10-01), Redl
Balakrishnan Balu
Djenguerian Alex B.
Hugh Matthews David Michael
Wong Kent
Blakely , Sokoloff, Taylor & Zafman LLP
Patel Rajnikant B.
Power Integrations, Inc.
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