QUASI-RESONANT FLY-BACK CONVERTER WITHOUT AUXILIARY WINDING

• US 20080278974A1
• Filed: 05/08/2007
• Published: 11/13/2008
• Est. Priority Date: 05/08/2007
• Status: Active Grant

• Current Assignee: Leadtrend Technology Corporation
• Original Assignee: Leadtrend Technology Corporation
• Inventors: Wu, Tsung-Hsiu
• Granted Patent: US 7,898,823 B2
• Time in Patent Office: Days
• US Class Current: 363/21.18
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 1/40 Means for preventing magnetic saturation
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

Disclosed is a switching converter without an auxiliary winding. The switching converter has a transformer, a switching transistor, a coupling circuit and a regulating circuit. The transformer has a primary winding and a secondary winding, and is for transforming an input voltage into an output voltage; a first end of the switching transistor is coupled to the primary winding of the transformer, and the switching transistor is for controlling an operation of the transformer according to a control signal; the coupling circuit is for coupling a signal at the first end of the switching transistor to generate a coupled signal; and the regulating circuit is for detecting the coupled signal to generate the control signal according to the detecting result.

Claims

1. A switching converter, comprising:

a transformer, comprising a primary winding and a secondary winding, for transforming an input voltage into an output voltage;

a switching transistor, a first end of which is coupled to the primary winding of the transformer and a control end of which is for receiving a control signal, for controlling operation of the transformer according to the control signal;

a coupling circuit, coupled to the switching transistor, for coupling a signal at the first end of the switching transistor to generate a coupled signal; and

a regulating circuit, coupled to the switching transistor and the coupling circuit, for detecting the coupled signal to generate a detecting result and generating the control signal according to the detecting result.

2. The switching converter of claim 1, wherein the coupling circuit is coupled between the switching transistor and a current sensing pin of the regulating circuit, wherein the current sensing pin is utilized to sense a current flow through the switching transistor when the switching transistor is on, and is utilized to detect a demagnetization of the transformer when the switching transistor is off.

3. The switching converter of claim 1, wherein the coupling circuit comprises a capacitive element, a first end of which is coupled to the first end of the switching transistor, and a second end of which is coupled to a second end of the switching transistor and the regulating circuit.

4. The switching converter of claim 1, wherein the regulating circuit comprises:

a zero-cross detecting circuit, coupled to the coupling circuit, for detecting a zero-crossing point of the coupled signal and generating the detecting result; and

a pulse width modulation (PWM) signal generator, coupled to the switching transistor, for generating the control signal to control the switching transistor according to the detecting result.

5. The switching converter of claim 4, wherein the regulating circuit further comprises:

a blanking circuit, coupled to the zero-cross detecting circuit and the PWM signal generator, for blanking the detecting result of the zero-cross detecting circuit during a blanking time period corresponding to a switching frequency of the switching converter.

6. The switching converter of claim 4, wherein the PWM signal generator generates the control signal when the zero-cross detecting circuit detects a zero crossing point on a rising edge of the coupled signal, and generates the control signal after a period of time when the zero-cross detecting circuit detects the zero crossing point on a falling edge of the coupled signal.

7. The switching converter of claim 1, further comprising an amplifying circuit, coupled to the regulating circuit, for amplifying the coupled signal input to the regulating circuit.

8. The switching converter of claim 7, wherein the amplifying circuit comprises a resistor, coupled between the regulating circuit and a current sensing resistor, and the resistance of the resistor is greater than that of the current sensing resistor.