PWM controller for controlling output power limit of a power supply
AssigneeSystem General Corp.
InventorsTa-yung Yang, Jenn-yu G. Lin, Shu-chung Yi
Life of this patent
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Abstract
A PWM controller has a line voltage input that allows using an input resistor for both start-up and power-limit compensation, thus saving the power consumption, easing the PCB layout, and shrinking the power supply size. In the integrated circuit, a mirrored-resistor used for the power limit compensation is composed of a mirror MOSFET, which is associated with an op amplifier, a constant voltage and a constant current to provide a precise resistance. Thus, by properly selecting the value of the input resistor, an identical output power limit for low line and high line voltage input can be achieved.
Claims3
A PWM controller for controlling an output power limit of a power supply, comprising:
- a current divider, having a first terminal connected to a line input voltage of the power supply via a startup resistor, a second terminal coupled to a supply voltage, and a third terminal;
- a mirror resistor, having a first terminal coupled between the third terminal of the current divider, and a second terminal coupled to a ground voltage;
- an adder, with a negative input terminal coupled between the third terminal of the current divider and the first terminal of the mirror resistor, a positive input terminal coupled to a reference voltage, and an output terminal;
- a first comparator, with a positive input terminal coupled to the output terminal of the adder, a negative input terminal, and an output terminal;
- a second comparator, with a positive input terminal coupled to the supply voltage, a negative terminal coupled to the negative terminal of the first comparator, and an output terminal;
- a NAND gate, with two input terminals coupled to the output terminals of the first and second comparators, and an output terminal;
- a flip flop, coupled to the output terminal of the NAND gate;
- and an oscillator, coupled to the flip flop.
Dependencies are inferred from the claim text.