Over power compensation in switched mode power supplies

• US 8,081,495 B2
• Filed: 11/20/2008
• Issued: 12/20/2011
• Est. Priority Date: 11/20/2008
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Inventors: Vecera, Ivo, Kadanka, Petr, Cyr, Nicolas
• Primary Examiner(s): Berhane, Adolf
• Assistant Examiner(s): Zhang, Jue
• Application Number:
  US12/275,011
• Publication Number:
  US 20100123447A1
• Time in Patent Office: 1,125 Days
• Field of Search: 363 2108- 2118
• US Class Current: 363/21.12
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• 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

Abstract

An over-power compensation circuit for use in a switched mode power supply having a current sense circuit for sensing a current flowing through a power transistor of the switched mode power supply. The over-power compensation circuit includes a peak detector, a sample-and-hold circuit, a current offset generator, and an offset resistor. The peak detector has an input for receiving an input voltage derived from the input line, and an output. The sample-and-hold circuit has an input connected to the output of the peak detector, and an output. The current offset generator has an input connected to the output of the sample-and-hold circuit, and an output for providing an offset current. The offset resistor has a first terminal connected to the output of the current offset generator, and a second terminal adapted to be connected to a current conducting electrode of the power transistor.

Claims

1. An over-power compensation circuit for use in a switched mode power supply for switching a current supplied from an input line through an inductance using a power transistor and having a current sense circuit for sensing a current flowing through the power transistor, comprising:

a peak detector having an input for receiving an input voltage derived from the input line, and an output, wherein said peak detector comprises;

a counter having an input, and an output;

a digital-to-analog converter having a first input, a second input coupled to said output of said counter, and an output;

a comparator having a first input coupled to said output of said digital-to-analog converter, a second input for receiving said input voltage derived from the input line, and an output;

a delay circuit having an input, and an output coupled to a reset terminal of said counter; and

a NAND gate having a first input coupled to an output of an oscillator, a second input coupled to the output of said comparator, and an output coupled to said input of said counter;

a sample-and-hold circuit having an input coupled to said output of said peak detector, and an output;

a current offset generator having an input coupled to said output of said sample-and-hold circuit, and an output for providing an offset current; and

an offset resistor having a first terminal coupled to said output of said current offset generator, and a second terminal adapted to be coupled to a current conducting electrode of the power transistor.

3. The over-power compensation circuit of claim 1, wherein said offset current is provided on a cycle-by-cycle basis of said input voltage.

2. An over-power compensation circuit for use in a switched mode power supply for switching a current supplied from an input line through an inductance using a power transistor and having a current sense circuit for sensing a current flowing through the power transistor, comprising:

a peak detector having an input for receiving an input voltage derived from the input line, and an output;

a sample-and-hold circuit having an input coupled to said output of said peak detector, and an output;

a current offset generator having an input coupled to said output of said sample-and-hold circuit, and an output for providing an offset current; and

an offset resistor having a first terminal coupled to said output of said current offset generator, and a second terminal adapted to be coupled to a current conducting electrode of the power transistor, wherein said sample-and-hold circuit comprises;

a memory having a input coupled to said output of said peak detector, and a output; and

a digital-to-analog converter having a first input, a second input coupled to said output of said memory, and an output coupled to said first terminal of said offset resistor.

4. An over-power compensation circuit for use in a switched mode power supply for switching a current supplied from an input line through an inductance using a power transistor and having a current sense circuit for sensing a current flowing through the power transistor, comprising:

a peak detector having an input for receiving an input voltage derived from the input line, and an output;

a sample-and-hold circuit having an input coupled to said output of said peak detector, and an output;

a current offset generator having an input coupled to said output of said sample-and-hold circuit, and an output for providing an offset current;

an offset resistor having a first terminal coupled to said output of said current offset generator, and a second terminal adapted to be coupled to a current conducting electrode of the power transistor;

a reset circuit having a first input for receiving the input voltage, and an output for providing a reset voltage to said peak detector and said sample-and-hold circuit; and

a watch-dog timer circuit having an input coupled to said output of said reset circuit, and an output coupled to a second input of said reset circuit, said watch-dog timer circuit adapted to reset said peak detector and said sample-and-hold circuit based on said reset voltage being in a single state for a predetermined amount of time.

5. The over-power compensation circuit of claim 4, wherein said reset voltage is in said single state for said predetermined amount of time said input voltage is a direct current voltage greater than a predetermined threshold.

6. An over-power compensation circuit for use in a switched mode power supply for switching a current supplied from an input voltage derived from an input line through an inductance using a power transistor and having a current sense circuit for sensing a current flowing through the power transistor, comprising:

a high-voltage sensing circuit adapted to detect a high-voltage level of the input voltage during a line cycle of the input voltage;

a sample-and-hold circuit adapted to store said high-voltage level of the input voltage;

a current offset generator for providing an offset current responsive to said high-voltage level stored by said sample-and-hold circuit;

an offset resistor having a first terminal for receiving said offset current, and a second terminal adapted to be coupled to a current conducting electrode of a power transistor, wherein said high-voltage sensing circuit comprises;

a counter having an input, and an output;

a digital-to-analog converter having a first input, a second input coupled to said output of said counter, and an output;

a comparator having a first input coupled to said output of said digital-to-analog converter, a second input for receiving said input voltage derived from the input line, and an output;

a delay circuit having an input, and an output coupled to a reset terminal of said counter; and

a NAND gate having a first input coupled to an output of an oscillator, a second input coupled to the output of said comparator, and an output coupled to said input of said counter.

7. The over-power compensation circuit of claim 6, wherein said sample-and-hold circuit comprises:

a memory having a input coupled to said output of said high-voltage sensing circuit, and a output; and

a digital-to-analog converter having a first input, a second input coupled to said output of said memory, and an output coupled to said first terminal of said offset resistor.

8. The over-power compensation circuit of claim 6, further comprising:

a reset circuit having a first input for receiving the input voltage, and an output for providing a reset voltage to said high-voltage sensing circuit and said sample-and-hold circuit.

9. The over-power compensation circuit of claim 8, further comprising:

a watch-dog timer circuit having an input coupled to said output of said reset circuit, and an output coupled to a second input of said reset circuit, said watch-dog timer circuit adapted to reset said peak detector and said sample-and-hold circuit based on said reset voltage being in a single state for a predetermined amount of time.

10. The over-power compensation circuit of claim 8, wherein said reset voltage is in said single state for said predetermined amount of time said input voltage is a direct current voltage greater than a predetermined threshold.