Universal pulse width modulating power converter

• US 6,344,980 B1
• Filed: 11/08/1999
• Issued: 02/05/2002
• Est. Priority Date: 01/14/1999
• Status: Expired due to Term

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Fairchild Semiconductor Corporation (ON Semiconductor Corporation)
• Inventors: Hwang, Jeffrey, Hsu, Calvin
• Primary Examiner(s): NGUYEN, MATTHEW VAN
• Application Number:
  US09/436,074
• Time in Patent Office: 820 Days
• Field of Search: 363/16, 363/20, 363/21.01, 363/21.04, 363/21.05, 363/21.07, 363/21.12, 363/21.13, 363/21.15, 363/95, 363/97, 363/131, 323/222
• US Class Current: 363/21.01
• CPC Class Codes: H02M 1/4258 using a single converter stage both for correction of AC input power factor and generation of a regulated and galvanically isolated DC output voltage H02M1/4241 takes precedence
• CPC Class Codes: H02M 3/1584 with a plurality of power processing stages connected in parallel
• 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

A controller for a pulse width modulating (PWM) power converter. The controller monitors an output voltage and a current through a magnetic element for modulating a duty cycle of a main power switch. The controller is an eight-pin integrated circuit which controls either a forward converter or a post regulator without internal modifications. The monitored current of the forward converter forms a positive sensing signal. The monitored current of the post regulator forms a negative sensing signal. A current sense circuit of the controller forms an absolute value of either sensing signal. A soft-start circuit of the controller forms a start-up voltage ramp which is proportional to the level of a V_CC supply without requiring an external capacitor. A duty cycle of the main switch is gradually increased by comparing the start-up voltage ramp to the absolute value of the sensing signal. A pulse skipping circuit of the controller disables switching of the main switch under light load conditions. An error signal representative of a difference between the output voltage and a desired output voltage is compared to a pulse skip reference voltage. When the error signal falls below the reference voltage, the main switch is disabled. Because the pulse skip reference voltage is inversely related to the V_CC supply, pulsing of the main switch under light load conditions is spread out in time. A clock signal utilized to control switching of the main switch is generated internally or externally to the integrated circuit.

Claims

1. A power converter having a magnetic element and a switch for selectively interrupting a current through the magnetic element wherein a controller for the switch comprises:

a. current sensing means for sensing the current through the magnetic element wherein the current sensing means receives a first voltage signal representative of the current through the magnetic element and wherein the current sensing means includes means for forming a second voltage signal representative of an absolute value of the first voltage signal whereby the first voltage signal can be positive or negative;

b. voltage sensing means for sensing an output voltage of the power converter; and

c. control means coupled to the first sensing means and to the second sensing means for controlling a duty cycle of the switch based upon the second voltage signal and the output voltage.

2. The power converter according to claim 1 wherein the magnetic element is a transformer having a primary winding and a secondary winding wherein the current through the magnetic element flows through a primary winding of the transformer and an induced current in the secondary winding is rectified for forming the output voltage.

3. The power converter according to claim 1 wherein the magnetic element is a transformer having a primary winding and a secondary winding wherein the current through the magnetic element flows through a secondary winding of the transformer and is induced by a current in the primary winding.

4. The power converter according to claim 3 wherein the transformer comprises one or more additional secondary windings and wherein the power converter further comprises one or more additional switches, one coupled to each additional secondary winding and one or more additional controllers, one coupled to control each switch based upon a current through the respective secondary winding thereby forming one or more additional output voltages, one for each additional secondary winding.

5. The power converter according to claim 1 wherein the magnetic element is a transformer having a primary winding and a secondary winding wherein when the first voltage signal is positive, the current through the magnetic element flows through a primary winding of the transformer and an induced current in the secondary winding is rectified for forming the output voltage, and wherein when the first voltage signal is negative, the current through the magnetic element flows through a secondary winding of the transformer and is induced by a current through a primary winding of the transformer.

6. The power converter according to claim 1 wherein the first voltage signal is formed across a resistor coupled in series with the magnetic element.

8. The power converter according to claim 6 wherein the resistor has a first terminal and a second terminal wherein the first voltage signal is formed at the first terminal and the second terminal is coupled to a ground node.

9. The power converter according to claim 8 wherein the first voltage signal is positive when the current through the magnetic element flows to the ground node and wherein the first voltage signal is negative when the current through the magnetic element flows from the ground node.

10. The power converter according to claim 9 wherein the magnetic element is a transformer having a primary winding and a secondary winding wherein when the first voltage signal is positive, the current through the magnetic element flows through a primary winding of the transformer and an induced current in the secondary winding is rectified for forming the output voltage, and wherein when the first voltage signal is negative, the current through the magnetic element flows through a secondary winding of the transformer and is induced by a current through a primary winding of the transformer.

11. The power converter according to claim 10 wherein the controller is an integrated circuit having no more than eight pins.

7. The power converter according to claim I further comprising current limit means for opening the switch when the first voltage signal rises above a first limit wherein the first limit is positive and opening the switch when the first voltage signal falls below a second limit wherein the second limit is negative.

12. A power converter having a magnetic element and a switch for selectively interrupting a current through the magnetic element wherein the power converter is selected from a group consisting of a forward converter and a post regulator, wherein an integrated circuit controller for the switch is configurable for the forward converter and for the post regulator without modification to the integrated circuit and wherein the integrated circuit comprises:

a. a current sensor for sensing the current through the magnetic element wherein the magnetic element is a primary winding of a transformer when the power converter is a forward converter and wherein the magnetic element is a secondary winding of the transformer when the power converter is a post-regulator;

b. voltage sensor for sensing an output voltage of the power converter; and

c. a switch control circuit coupled to the current sensor and to the voltage sensor for controlling a duty cycle of the switch based upon the current through the magnetic element and the output voltage.

13. The power converter according to claim 12 wherein the current sensor receives a first voltage signal representative of the current through the magnetic element and wherein the first voltage signal is positive when the magnetic element is the primary winding and wherein the first voltage signal is negative when the magnetic element is the secondary winding.

14. The power converter according to claim 13 wherein the current sensor includes means for forming a second voltage signal representative of an absolute value of the first voltage signal.

15. The power converter according to claim 12 wherein the integrated circuit controller has no more than eight pins.