PWM controller with constant output power limit for a power supply

• US 7,099,163 B1
• Filed: 11/14/2005
• Issued: 08/29/2006
• Est. Priority Date: 11/14/2005
• Status: Active Grant

• Current Assignee: BCD Shanghai Micro-Electronics Company Limited
• Original Assignee: BCD Semiconductor Manufacturing Limited (Diodes Incorporated)
• Inventors: Ying, Zheng
• Primary Examiner(s): BERHANE, ADOLF D
• Application Number:
  US11/271,901
• Time in Patent Office: 288 Days
• Field of Search: 363/20, 363/21.01, 363/21.1, 363/21.11, 363/21.18, 363/41, 363/49
• US Class Current: 363/21.11
• CPC Class Codes: H02M 1/36 Means for starting or stopping converters
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop

Abstract

A PWM controller has a line voltage input that allows using a start-up resistor for both start-up and power-limit compensations so that it can save the power consumption, ease the PCB layout, and shrink the power supply size. In the integrated circuit, a current switch used for both start-up and line voltage sensing is composed of a diode and a switch transistor. A current multiplier is used to improve the precise by canceling the impact of the integrated resistor'"'"'s absolute value, which is composed of a transistor loop, a constant current and a reference current. Thus, by properly selecting the value of the start-up resistor, an identical output power limit for low line and high line voltage input can be achieved.

Claims

1. A PWM controller for controlling an output power limit of a power supply, comprising:

a current switch unit, having a first terminal connected to a line input voltage of the power supply via a start-up resistor, a second terminal coupled to a power supply voltage, a third terminal connected to an under-voltage lockout unit, and a four terminal;

a current multiplier, having a first terminal coupled to the four terminal of the current switch unit, and a second terminal;

an adder, having a negative input terminal coupled to the second terminal of the current multiplier, a positive input terminal coupled to a reference current, and an output terminal;

a resistor, having a first terminal coupled between the third terminal of the adder, and a second terminal coupled to a ground voltage;

a buffer, having a input terminal coupled between the output terminal of the adder and the first terminal of the resistor, and an output terminal;

a first comparator, having a positive input terminal coupled to the output terminal of the buffer, a negative input terminal, and an output terminal;

a second comparator, having 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, having two input terminals coupled to the output terminals of the first and second comparators, and an output terminal; and

a flip flop, coupled to the output terminal of the NAND gate; and

an oscillator, coupled to the flip flop.

2. The PWM controller of claim 1, wherein the current switch unit comprising:

a diode, having a anode connected to the input voltage, a cathode connected to the power supply voltage; and

a switch transistor, having a gate terminal connected to the under-voltage lockout unit, a drain to the input voltage, and a source terminal connected to the adder.