Universal pulse width modulating power converter

• US 6,469,914 B1
• Filed: 10/04/2001
• Issued: 10/22/2002
• 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
• Application Number:
  US09/971,844
• Time in Patent Office: 383 Days
• Field of Search: 363/16, 363/20, 363/21.01, 363/21.04, 363/95, 363/97, 363/131, 323/301, 323/303
• 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 thereby forming an output voltage wherein a controller for the switch comprises:

a. a control means coupled to the switch for controlling a duty cycle of the switch for regulating the output voltage; and

b. switching inhibiting means comprising a pulse skip circuit for generating a logic signal to inhibit switching of the switch when a difference between the output voltage and a desired level for the output voltage falls below a threshold and wherein the threshold is inversely related to a supply voltage.

2. The power converter according to claim 1 wherein the supply voltage is representative of a level of an input voltage provided to the power converter.

3. The power converter according to claim 2 wherein the supply voltage is formed by the power converter.

4. The power converter according to claim 1 wherein the threshold (V_SKIP) is given by:

5. A power converter having a magnetic element and a switch for selectively interrupting a current through the magnetic element thereby forming an output voltage wherein a controller for the switch comprises:

a. first sensor for sensing a current through the magnetic element;

b. second sensor for sensing the output voltage;

c. a switch control circuit coupled to the first sensor and to the second sensor for controlling a duty cycle of the switch based upon the current and the output voltage; and

d. switching inhibiting circuit comprising a pulse skip circuit for generating a logic signal to inhibit switching of the switch when a difference between the output voltage and a desired level for the output voltage falls below a threshold and wherein the threshold is inversely related to a supply voltage.

6. The power converter according to claim 5 wherein the supply voltage is representative of a level of an input voltage provided to the power converter.

7. The power converter according to claim 6 wherein the supply voltage is formed by the power converter.

8. The power converter according to claim 5 wherein the threshold (V_SKIP) is given by: