Charger circuit and PWM controller thereof

• US 20080007226A1
• Filed: 01/03/2007
• Published: 01/10/2008
• Est. Priority Date: 06/16/2006
• Status: Active Grant

• Current Assignee: BCD Shanghai Micro-Electronics Company Limited
• Original Assignee: BCD Semiconductor Manufacturing Limited (Diodes Incorporated)
• Inventors: Peng, Tao, Lu, Shu-Zhuang
• Granted Patent: US 7,583,061 B2
• Time in Patent Office: Days
• US Class Current: 320/141
• CPC Class Codes: H02J 7/00304 Overcurrent protection
• CPC Class Codes: H02J 7/00712 the cycle being controlled or terminated in response to electric parameters

Abstract

A PWM controller includes a short circuit mode circuit which has input ends connecting simultaneously to a power supply input end and an output end of an output driving circuit, and an oscillator which has a temperature compensation circuit that includes a medium value multi-transistor resistor of a negative temperature coefficient and a well resistor of a positive temperature coefficient. The invention also provides a charger circuit which includes the PWM controller set forth above and a constant voltage/current control circuit coupling with the PWM controller through a transformer. A system adopted the PWM controller circuit and charger circuit of the invention does not need a voltage stabilization diode now equipped in many conventional designs. The invention provides an improved short circuit protection, eliminates low frequency harmonic waves, packages power transistors and the controller into a single TO-94, increases the cluster density and enhances the reliability of small packages.

Claims

1. A PWM controller, comprising the characteristic that a short circuit mode circuit has input ends connecting respectively and simultaneously to a power supply input end and an output end of an output driving circuit, and an oscillator which has a temperature compensation circuit which includes a medium value multi-transistor resistor of a negative temperature coefficient and a well resistor of a positive temperature coefficient.

2. The PWM controller of claim 1 further comprising:

a power on circuit which is connected to the power supply input end and determines an interim threshold duty voltage of the power supply input end at the power on stage and a minimum duty voltage during normal operation;

the oscillator which generates a square wave signal at a constant frequency and has an output end connecting to a PWM logic circuit and a positive and negative temperature compensation circuit to generate the constant frequency used by a power supply;

a current limit comparator which has an input end connecting to the power supply input end in response to a current sampling signal of the output driving circuit to carry out feedback of a current circuit, and responds to voltage variations of the power supply input end to carry out feedback of a voltage circuit, current feedback signals and voltage feedback signals being sent to the PWM logic circuit in an error signal format through the current limit comparator;

the PWM logic circuit which is connected to the oscillator to respond to the square wave signal output therefrom and is connected to the current limit comparator to receive error signals thereof to determine duty cycle of output driving pulses, and responds to input signals of the short circuit mode circuit and periodically stops output signals to protect the system;

the short circuit mode circuit which has one input end connecting to the power supply input end and another input end connecting to the output end of the output driving circuit;

during the normal operation the voltage at the output end of the output driving circuit is higher and the voltage at the power supply input end is lower;

in the event of short circuit or a light loading condition and the output end voltage of the output driving circuit is lower and the voltage at the power supply input end is higher;

the short circuit mode circuit making the PWM controller to enter a short circuit protection mode; and

the output driving circuit which has an input end connecting to the PWM logic circuit and output ends connecting to the short circuit mode circuit and the current limit comparator, and generates PWM pulse signals and is connected to and drives a power transistor outside the PWM controller through power elements located in the PWM controller.

3. The PWM controller of claim 2, wherein the power elements in the PWM controller are built-in power transistors.

4. The PWM controller of claim 3, wherein the power transistors and the PWM controller are package in a TO-94.

5. The PWM controller of claim 2, wherein the power on circuit does not include a voltage stabilization diode.

6. A charger circuit comprising a PWM controller and a constant voltage and constant current control circuit coupled with the PWM controller through a transformer, wherein:

the PWM controller has a short circuit mode circuit which has input ends connecting respectively and simultaneously to a power supply input end and an output end of an output driving circuit, and an oscillator which has a temperature compensation circuit which includes a medium value multi-transistor resistor of a negative temperature coefficient and a well resistor of a positive temperature coefficient.

7. The charger circuit of claim 6, wherein the PWM controller includes:

a power on circuit which is connected to the power supply input end and determines an interim threshold duty voltage of the power supply input end at the power on stage and a minimum duty voltage during normal operation;

the oscillator which generates a square wave signal at a constant frequency and has an output end connecting to a PWM logic circuit and a positive and negative temperature compensation circuit to generate the constant frequency used by a power supply;

a current limit comparator which has an input end connecting to the power supply input end in response to a current sampling signal of the output driving circuit to carry out feedback of a current circuit, and responds to voltage variations of the power supply input end to carry out feedback of a voltage circuit, current feedback signals and voltage feedback signals being sent to the PWM logic circuit in an error signal format through the current limit comparator;

the PWM logic circuit which is connected to the oscillator to respond to the square wave signal output therefrom and is connected to the current limit comparator to receive error signals thereof to determine duty cycle of output driving pulses, and responds to input signals of the short circuit mode circuit and periodically stops output signals to protect the system;

the short circuit mode circuit which has one input end connecting to the power supply input end and another input end connecting to the output end of the output driving circuit;

during the normal operation the voltage at the output end of the output driving circuit is higher and the voltage at the power supply input end is lower;

in the event of short circuit or a light loading condition and the output end voltage of the output driving circuit is lower and the voltage at the power supply input end is higher;

the short circuit mode circuit making the PWM controller to enter a short circuit protection mode; and

the output driving circuit which has an input end connecting to the PWM logic circuit and output ends connecting to the short circuit mode circuit and the current limit comparator, and generates PWM pulse signals and is connected to and drives a power transistor outside the PWM controller through power elements located in the PWM controller.

8. The charger circuit of claim 7, wherein the power elements in the PWM controller are built-in power transistors.

9. The charger circuit of claim 8, wherein the power on circuit does not include a voltage stabilization diode.

10. The charger circuit of claim 9, wherein the constant voltage and constant current control circuit provides short circuit control.