Switched mode power supply with programmable skipping mode

• US 6,385,061 B1
• Filed: 02/12/2001
• Issued: 05/07/2002
• Est. Priority Date: 02/11/2000
• Status: Expired due to Term

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Inventors: Sukup, Frantisek, Turchi, Joel
• Primary Examiner(s): Vu, Bao Q.
• Application Number:
  US09/855,202
• Time in Patent Office: 449 Days
• Field of Search: 363/21.01, 363/21.12, 363/21.15, 363/21.17, 363/95, 363/97, 363/131, 323/902
• US Class Current: 363/21.15
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 1/0032 Control circuits allowing low power mode operation, e.g. in standby mode
• CPC Class Codes: H02M 1/34 Snubber circuits
• CPC Class Codes: H02M 1/348 Passive dissipative snubbers
• CPC Class Codes: H02M 1/36 Means for starting or stopping converters
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence
• 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
• CPC Class Codes: Y10S 323/902 Optical coupling to semiconductor

Abstract

A method and a power conversion apparatus having a substantially direct current input voltage, an output transformer having a primary inductor and at least a secondary winding, and a transistor for controlling the transfer of energy from the primary inductor to the secondary winding and coupled to a controller for switching the transistor on and off at a predetermined rate. A sensor for sensing the power required at the output of the conversion apparatus and for generating a voltage representative thereof is provided, as is provided a sensor for sensing the peak current in the primary inductor and for developing a voltage representative thereof. The controller contains a circuit for inhibiting selected on-cycles of the transistor when the power demand from the output of the conversion apparatus is less than the desired peak current in the primary inductor, the circuit comprising a comparator, a current source for developing a biasing voltage representative of the desired peak current in the primary inductor across a resistor external to the controller during the time when the transistor is switched off, means for receiving the voltage representative of the power required, comparing the biasing voltage to the voltage representative of the power required at the output, and having the output of the comparator coupled to the gate of the transistor for causing the transistor to skip on-cycles when the power demand from the output is below that power the biasing voltage is representative of.

Claims

1. In a power conversion apparatus having a substantially direct current input voltage, an output transformer having a primary inductor and at least a secondary winding, and a transistor for controlling the transfer of energy from the primary inductor to the secondary winding and coupled to a controller for switching the transistor on and off at a predetermined rate, a sensor for sensing the power required at the output of the conversion apparatus and for generating a voltage representative thereof, a sensor for sensing the peak current in the primary inductor and for developing a voltage representative thereof, the controller containing a circuit for inhibiting selected on-cycles of the transistor, the circuit comprising:

a comparator,

a current source for developing a biasing voltage representative of the desired peak current in the primary inductor across a resistor external to the controller during the time when the transistor is switched off,

means for receiving the voltage representative of the power required and for applying the voltage representative of the power required to the comparator,

means for applying the biasing voltage to the comparator for comparing the biasing voltage to the voltage representative of the power required at the output,

the output of the comparator coupled to the gate of the transistor for causing the transistor to skip on-cycles when the power required at the output is below the power the biasing voltage is representative of.

2. In a switched mode power supply having a rectifier for rectifying an AC input voltage to produce a rectified in put voltage, an output transformer having a primary inductor and at least a secondary winding, and a transistor for controlling the transfer of energy from the primary inductor to the secondary winding and coupled to a controller for switching the transistor on and off at a predetermined rate, a sensor for sensing the power required at the output of the power supply and for generating a voltage representative thereof, a sensor for sensing the peak current in the primary inductor and for developing a voltage representative thereof, the controller containing a circuit for inhibiting selected on-cycles of the transistor, the circuit comprising:

a comparator,

a current source for developing a biasing voltage representative of the desired peak current in the primary inductor across a resistor external to the controller during the time when the transistor is switched off,

means for receiving the voltage representative of the power required and for applying the voltage representative of the power required to the comparator,

means for applying the biasing voltage to the comparator for comparing the biasing voltage to the voltage representative of the power required at the output,

the output of the comparator coupled to the gate of the transistor for causing the transistor to skip on-cycles when the power required at the output is below the power the biasing voltage is representative of.

3. A circuit as set forth in claim 2 further comprising:

means for receiving the voltage representative of the peak current during the time when the transistor is switched on and applying the voltage representative of the peak current to the comparator, and

the comparator comparing the voltage representative of the power required at the output to the voltage representative of the peak current to turn off the transistor when the desired peak current through the primary inductor has been reached.

4. A circuit as set forth in claim 3 wherein the means for receiving the voltage representative of the peak current and the means for receiving the biasing voltage are a common input to the controller.

5. A circuit as set forth in claim 2 wherein the output of the comparator is coupled to a logic gate, and the output of the logic gate is coupled to the gate of the transistor, and wherein the output of the logic gate controls the time of application of the current source to the external resistor.

6. In a power conversion apparatus having a substantially direct current input voltage, an output transformer having a primary inductor and at least a secondary winding, and a transistor for controlling the transfer of energy from the primary inductor to the secondary winding and coupled to a controller for switching the transistor on and off at a predetermined rate, a sensor for sensing the power required at the output of the conversion apparatus and for generating a voltage representative thereof, a sensor for sensing the peak current in the primary inductor and for developing a voltage representative thereof, a method for inhibiting selected on-cycles of the transistor, the method comprising:

providing a current source for developing a biasing voltage representative of the desired peak current in the primary inductor across a resistor external to the controller during the time when the transistor is switched off,

receiving the voltage representative of the power required,

comparing the voltage representative of the power required to the biasing voltage,

using the comparison coupled for causing the transistor to skip on-cycles when the power required at the output is below the power the biasing voltage is representative of.

7. A method as set forth in claim 6 further comprising:

receiving the voltage representative of the peak current during the time when the transistor is switched on, and comparing the voltage representative of the power required at the output to the voltage representative of the peak current to turn off the transistor when the desired peak current through the primary inductor has been reached.

8. A method as set forth in claim 7 wherein the voltage representative of the peak current and the biasing voltage are provided on a common input to the controller.

9. A method as set forth in claim 8 wherein the comparison is used to control the switching of the transistor.