PHASE ANGLE MEASUREMENT OF A DIMMING CIRCUIT FOR A SWITCHING POWER SUPPLY

• US 20110194311A1
• Filed: 02/09/2010
• Published: 08/11/2011
• Est. Priority Date: 02/09/2010
• Status: Active Grant

• Current Assignee: Power Integrations Incorporated
• Original Assignee: Power Integrations Incorporated
• Inventors: Mao, Mingming, Gaknoki, Yury, Pastore, Tiziano
• Granted Patent: US 8,102,683 B2
• Time in Patent Office: Days
• US Class Current: 363/21.12
• CPC Class Codes: G05F 1/455 with phase control
• 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: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop
• CPC Class Codes: H02M 7/217 using semiconductor devices only
• CPC Class Codes: H05B 41/2827 using specially adapted components in the load circuit, e.g. feed-back transformers, piezoelectric transformers; using specially adapted load circuit configurations
• CPC Class Codes: H05B 41/3922 and measurement of the incident light
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/382 with galvanic isolation between input and output
• CPC Class Codes: H05B 45/385 using flyback topology
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

An example controller for a switched mode power supply includes a zero-crossing detector, a feedback reference circuit, and a drive signal generator. The zero-crossing detector is coupled to generate a zero-crossing signal representative of a length of time that a zero-crossing condition of an input voltage of the power supply exists. The feedback reference circuit is to be coupled to receive a feedback signal and a reference signal, where the feedback signal is representative of an output of the power supply and where the controller is adapted to adjust the reference signal in response to the length of time that the zero-crossing condition exists. The drive signal generator is to be coupled to control switching of a switch included in the power supply in response to an output of the feedback reference circuit to regulate an output of the power supply.

Claims

1. A controller for a switched mode power supply, the controller comprising:

a zero-crossing detector coupled to generate a zero-crossing signal representative of a length of time that a zero-crossing condition of an input voltage of the power supply exists;

a feedback reference circuit to be coupled to receive a feedback signal and a reference signal, wherein the feedback signal is representative of an output of the power supply and wherein the controller is adapted to adjust the reference signal in response to the length of time that the zero-crossing condition exists; and

a drive signal generator to be coupled to control switching of a switch included in the power supply in response to an output of the feedback reference circuit to regulate an output of the power supply.

2. The controller of claim 1, wherein the zero-crossing detector generates the zero-crossing signal in response to comparing a voltage sense signal representative of the input voltage with a zero-crossing reference.

3. The controller of claim 1, wherein the zero-crossing signal indicates that a zero-crossing condition exists when a magnitude of the input voltage of the power supply is less than a zero-crossing voltage threshold.

4. The controller of claim 1, wherein the zero-crossing detector generates the zero-crossing signal in response to comparing a current sense signal with a zero-crossing reference, wherein the current sense signal is representative of a switch current flowing through the switch.

5. The controller of claim 1, wherein the input voltage is a dimmer output voltage, the controller further comprising:

a counter coupled to generate a phase count representative of a phase angle of the dimmer output voltage in response to the zero-crossing signal; and

a digital-to-analog converter (DAC) coupled to generate the reference signal in response to the phase count.

6. The controller of claim 5, wherein the DAC comprises:

a plurality of current sources; and

a plurality of switches, wherein each switch is coupled to a respective current source and configured to couple its respective current source to provide current to a reference current signal in response to a respective binary digit of the phase count, wherein the reference signal is representative of the reference current signal.

7. The controller of claim 6, wherein the plurality of current sources are binary-weighted current sources.

8. The controller of claim 5, further comprising an offset block coupled to the DAC to provide a non-zero offset amount such that an output of the offset block is zero when the phase count is less than the offset amount.

9. The controller of claim 5, further comprising a line synchronized oscillator coupled to the counter to provide a system clock, wherein the system clock has a constant cycle count for each half line cycle of the input voltage independent of a frequency of the input voltage.

10. The controller of claim 9, wherein the line synchronized oscillator adjusts a frequency of the clock signal in response to the zero-crossing signal.

11. The controller of claim 1, wherein the controller and the switch are included in an integrated circuit.

12. A switched mode power supply, comprising:

a switch;

an energy transfer element coupled to the switch and coupled to receive a dimmer output voltage;

a controller coupled to the switch to regulate an output of the power supply in response to the dimmer output voltage, wherein the controller includes;

a zero-crossing detector coupled to generate a zero-crossing signal representative of a length of time that a zero-crossing condition of the dimmer output voltage exists;

a feedback reference circuit coupled to receive a feedback signal and a reference signal, wherein the feedback signal is representative of the output of the power supply and wherein the controller is adapted to adjust the reference signal in response to the length of time that the zero-crossing condition exists; and

a drive signal generator coupled to control switching of the switch in response to the output of the feedback reference circuit to regulate the output of the power supply.

13. The power supply of claim 12, further comprising a dimmer circuit coupled to the energy transfer element to provide the dimmer output voltage having a phase angle.

14. The power supply of claim 13, wherein the dimmer circuit is a triac dimmer circuit.

15. The power supply of claim 12, wherein the output of the power supply is to be coupled to a load that includes an array of light emitting diodes.

16. The power supply of claim 12, wherein the zero-crossing detector generates the zero-crossing signal in response to comparing a voltage sense signal representative of the dimmer output voltage with a zero-crossing reference.

17. The power supply of claim 12, wherein the zero-crossing signal indicates that a zero-crossing condition exists when a magnitude of the dimmer output voltage is less than a zero-crossing voltage threshold.

18. The power supply of claim 12, wherein the controller further comprises:

a counter coupled to generate a phase count representative of a phase angle of the dimmer output voltage in response to the zero-crossing signal; and

a digital-to-analog converter (DAC) coupled to generate the reference signal in response to the phase count.

19. The power supply of claim 18, further comprising a line synchronized oscillator coupled to the counter to provide a system clock, wherein the system clock has a constant cycle count for each half line cycle of the input voltage independent of a frequency of the input voltage.

20. The power supply of claim 19, wherein the line synchronized oscillator adjusts a frequency of the clock signal in response to the zero-crossing signal.

21. The power supply of claim 18, wherein the DAC comprises:

a plurality of current sources; and

a plurality of switches, wherein each switch is coupled to a respective current source and configured to couple its respective current source to provide current to a reference current signal in response to a respective binary digit of the phase count, wherein the reference signal is representative of the reference current signal.

22. The power supply of claim 21, wherein the plurality of current sources are binary-weighted current sources.

23. The power supply of claim 21, wherein the controller further comprises an offset block coupled to the DAC to provide a non-zero offset amount such that an output of the offset block is zero when the phase count is less than the offset amount.

24. The power supply of claim 12, wherein the controller and the switch are included in an integrated circuit.