Triac dimmer compatible switching mode power supply and method thereof

• US 8,581,518 B2
• Filed: 05/18/2011
• Issued: 11/12/2013
• Est. Priority Date: 05/19/2010
• Status: Active Grant

• Current Assignee: Monolithic Power Systems Incorporated
• Original Assignee: Monolithic Power Systems Incorporated
• Inventors: Kuang, Naixing, Du, Lei, Zhang, Junming, Ren, Yuancheng
• Primary Examiner(s): CRAWFORD, JASON
• Application Number:
  US13/110,719
• Publication Number:
  US 20110285301A1
• Time in Patent Office: 909 Days
• Field of Search: 315/185.R, 315/186, 315/200.R, 315/201, 315/209.R, 315/224, 315/291, 315/294, 315246-247, 315/287
• US Class Current: 315/307
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/355 Power factor correction [PFC]; Reactive power compensation
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: H05B 45/38 using boost topology
• 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: H05B 45/39 Circuits containing inverter bridges

Abstract

Triac dimmer compatible switching mode power supplies used as LED drivers are disclosed herein. A PFC controller is configured in the switching mode power supplies. With the PFC controller, the current keeping the triac in the on-state is supplied by the DC/DC converter, and the LC resonance is reduced.

Claims

1. A switching mode power supply, comprising:

a triac dimmer, wherein the triac dimmer configured to receive an AC input signal and to modify the AC input signal with a target phase angle to generate a shaped AC signal;

a rectifier coupled to the triac dimmer to receive the shaped AC signal, the rectifier being configured to generate a rectified signal based on the shaped AC signal;

a filter coupled to the rectifier, the filter being configured to receive the rectified signal and generate a filtered signal;

a DC/DC converter coupled to the filter to receive the filtered signal, and wherein the DC/DC converter is configured to provide power to a load;

a dimming signal generator coupled to the rectifier to receive the rectified signal, the dimming signal generator being configured to generate a dimming signal based on the rectified signal;

a feedback circuit coupled to the DC/DC converter to generate a feedback signal indicative of the power provided to the load by the DC/DC converter; and

a PFC controller having a first input terminal, a second input terminal, a third input terminal, a fourth input terminal, and an output terminal, wherein;

the first input terminal is coupled to the dimming signal generator to receive the dimming signal;

the second input terminal is coupled to the rectifier to receive the rectified signal;

the third input terminal is coupled to the DC/DC converter to receive a sense signal indicative of a current flowing through the DC/DC converter;

the fourth input terminal is coupled to the feedback circuit to receive the feedback signal; and

based on the dimming signal, the rectified signal, the sense signal, and the feedback signal, the PFC controller provides a switching signal at the output terminal to the DC/DC converter.

2. The switching mode power supply of claim 1, wherein the DC/DC converter comprises a flyback converter.

3. The switching mode power supply of claim 2, wherein the feedback circuit comprises an average load current calculator having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal is coupled to the logic circuit to receive the switching signal, the second input terminal is coupled to the primary winding to receive the sense signal, and wherein based on the switching signal and the sense signal, the average load current calculator provides the feedback signal.

4. The switching mode power supply of claim 3, wherein the average load current calculator comprises:

an inverter configured to receive the switching signal, and wherein based on the switching signal, the inverter generates an inverse signal of the switching signal;

a first switch having a first terminal and a second terminal, wherein the first terminal is configured to receive the sense signal;

a second capacitor coupled between the second terminal of the first switch and ground;

a second switch having a first terminal and a second terminal, wherein the first terminal of the second switch is coupled to the second terminal of the first switch, and a square-wave signal is provided at the second terminal;

a third switch, coupled between the second terminal of the second switch and the primary side ground; and

an integrator having an input terminal and an output terminal, wherein the input terminal is coupled to the second terminal of the second switch to receive the square-wave signal, and wherein based on the square-wave signal, the integrator generates the feedback signal at the output terminal, and further wherein

the first switch and the third switch are controlled by the switching signal;

the second switch is controlled by the inverse signal of the switching signal; and

the feedback signal is provided at the output terminal of the integrator.

5. The switching mode power supply of claim 1, wherein the dimming signal generator comprises a first comparator having a first input terminal, a second input terminal, and an output terminal, and wherein the first input terminal is coupled the rectifier to receive the rectified signal, the second input terminal is coupled to a reference signal, and wherein based on the rectified signal and the reference signal, the first comparator provides the dimming signal at the output terminal.

6. The switching mode power supply of claim 1, wherein the PFC controller further comprises:

an oscillator configured to provide a set signal;

an error amplifier having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal is coupled to the dimming signal generator to receive the dimming signal, the second input terminal is coupled to the feedback circuit to receive the feedback signal, and wherein based on the dimming signal and the feedback signal, the error amplifier provides an error amplified signal;

a multiplier having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal is coupled to the rectifier to receive the rectified signal, the second input terminal is coupled to the error amplifier to receive the error amplified signal, and wherein based on the rectified signal and the error amplified signal, the multiplier provides an arithmetical signal at the output terminal;

a second comparator having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal is coupled to the multiplier to receive the arithmetical signal, the second input terminal is coupled to the DC/DC converter to receive the sense signal, and wherein based on the arithmetical signal and the sense signal, the second comparator provides a reset signal; and

a logic circuit having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal is coupled to the second comparator to receive the reset signal, the second input terminal is coupled to the oscillator to receive the set signal, and wherein based on the reset signal and the set signal, the logic circuit provides the switching signal to the DC/DC converter.

7. The switching mode power supply of claim 1, wherein the PFC controller comprises:

an error amplifier having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal is coupled to the dimming signal generator to receive the dimming signal, the second input terminal is coupled to the feedback circuit to receive the feedback signal, and wherein based on the dimming signal and the feedback signal, the error amplifier provides an error amplified signal;

a multiplier having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal is coupled to the rectifier to receive the rectified signal, the second input terminal is coupled to the error amplifier to receive the error amplified signal, and wherein based on the rectified signal and the error amplified signal, the multiplier provides an arithmetical signal at the output terminal;

a second comparator having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal is coupled to the multiplier to receive the arithmetical signal, the second input terminal is coupled to the DC/DC converter to receive the sense signal, and wherein based on the arithmetical signal and the sense signal, the second comparator provides a reset signal;

a zero current detector configured to detect a current flowing through the energy storage component, wherein the zero current detector generates the set signal based on the detection; and

a logic circuit having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal is coupled to the second comparator to receive the reset signal, the second input terminal is coupled to the zero current detector to receive the set signal, and wherein based on the reset signal and the set signal, the logic circuit provides the switching signal to the DC/DC converter.

8. A switching mode power supply, comprising:

a triac dimmer configured to receive an AC input voltage and modify the AC input voltage with a target phase angle to generate a shaped AC signal;

a rectifier coupled to the triac dimmer to receive the shaped AC signal, the rectifier being configured to generate a rectified signal based on the shaped AC signal;

a filter coupled to the rectifier to filter the rectified signal to generate a filtered signal;

a DC/DC converter coupled to the filter to receive the filtered signal, and wherein the DC/DC converter having a main switch operating in ON and OFF states to provide power to a load;

a dimming signal generator comprising a first comparator having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal is coupled to the rectifier to receive the rectified signal, the second input terminal is coupled to a reference signal with constant value, and wherein based on the rectified signal and the reference signal, the first comparator provides the dimming signal at the output terminal;

a feedback circuit coupled to the DC/DC converter to generate a feedback signal indicative of the power supplied to the load by the DC/DC converter; and

a PFC controller having a first input terminal, a second input terminal and an output terminal, wherein the first input terminal is coupled to the dimming signal generator to receive the dimming signal, the second input terminal is coupled to the feedback circuit to receive the feedback signal, and wherein based on the dimming signal and the feedback signal, the PFC controller provides a switching signal at the output terminal to control the main switch.

9. The switching mode power supply of claim 8, wherein the DC/DC converter comprises a flyback converter.

10. The switching mode power supply of claim 8, wherein the PFC controller comprises:

an oscillator configured to provide a set signal;

an error amplifier having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal is coupled to the dimming signal generator to receive the dimming signal, the second input terminal is coupled to the feedback circuit to receive the feedback signal, and wherein based on the dimming signal and the feedback signal, the error amplifier provides an error amplified signal;

an on-time controller having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal is coupled to the oscillator to receive the set signal, the second input terminal is coupled to the error amplifier to receive the error amplified signal, and wherein based on the set signal and the error amplified signal, the on-time controller provides a reset signal at the output terminal; and

a logic circuit having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal is coupled to the on-time controller to receive the reset signal, the second input terminal is coupled to the oscillator to receive the set signal, and wherein based on the reset signal and the set signal, the logic circuit provides a switching signal to control the main switch of the DC/DC converter.

11. The switching mode power supply of claim 8, wherein the PFC controller comprises:

a zero current detector configured to detect a current flowing through the energy storage component, wherein the zero current detector generates the set signal based on the detection;

an error amplifier having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal is coupled to the dimming signal generator to receive the dimming signal, the second input terminal is coupled to the feedback circuit to receive the feedback signal, and wherein based on the dimming signal and the feedback signal, the error amplifier provides an error amplified signal;

an on-time controller having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal is coupled to the zero current detector to receive the set signal, the second input terminal is coupled to the error amplifier to receive the error amplified signal, and wherein based on the set signal and the error amplified signal, the on-time controller provides a reset signal at the output terminal; and

a logic circuit having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal is coupled to the on-time controller to receive the reset signal, the second input terminal is coupled to the zero current detector to receive the set signal, and wherein based on the reset signal and the set signal, the logic circuit provides a switching signal to control the main switch.

12. The switching mode power supply of claim 8, wherein the feedback circuit comprises an average load current calculator having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal is coupled to the logic circuit to receive the switching signal, the second input terminal is coupled to the main switch to receive the sense signal, and wherein based on the switching signal and the sense signal, the average load current calculator provides the feedback signal.

13. The switching mode power supply of claim 12, wherein the average load current calculator comprises:

an inverter, configured to receive the switching signal, and wherein based on the switching signal, the inverter generates an inverse signal of the switching signal;

a first switch having a first terminal, a second terminal, wherein the first terminal receives the sense signal;

a second capacitor, coupled between the second terminal of the first switch and the ground;

a second switch having a first terminal and the second terminal, wherein the first terminal of the second switch is coupled to the second terminal of the first switch, and a square-wave signal is provided at the second terminal;

a third switch, coupled between the second terminal of the second switch and the primary side ground; and

an integrator having an input terminal and a output terminal, wherein the input terminal is coupled to the second terminal of the second switch to receive the square-wave signal, based on the square-wave signal, the integrator generates the feedback signal at the output terminal, and wherein

the first switch and the third switch are controlled by the switching signal,

the second switch is controlled by the inverse signal of the switching signal, and

the feedback signal is provided at the output terminal of the integrator.

14. A method of controlling a switching mode power supply, comprising:

coupling an AC input signal to a triac dimmer, to modify the AC input signal with a target phase angle to get a shaped AC signal;

rectifying the shaped AC signal to generate a rectified signal;

filtering the rectified signal to generate a filtered signal;

coupling the filtered signal to a DC/DC converter to provide power to a load, wherein the DC/DC converter has a main switch operating in ON and OFF states;

coupling the rectified signal to a dimming signal generator to generate a dimming signal;

sensing a current flowing through the main switch to generate a sense signal;

generating a feedback signal indicative of the power supplied to the load; and

generating a switching signal in response to the rectified signal, the dimming signal, the sense signal, and the feedback signal to control the main switch.

15. The method of claim 14, wherein the step of generating the switching signal in response to the rectified signal, the dimming signal, the sense signal, and the feedback signal comprises:

amplifying the difference between the dimming signal and the feedback signal to generate an error amplified signal;

multiplying the error amplified signal with the rectified signal to generate an arithmetical signal;

comparing the arithmetical signal with the sense signal to generate a reset signal;

generating an oscillation signal as a set signal; and

generating the switching signal based on the reset signal and the set signal.

16. The method of claim 14, wherein the step of generating a switching signal in response to the rectified signal, the dimming signal, the sense signal, and the feedback signal comprises:

amplifying the difference between the dimming signal and the feedback signal to generate an error amplified signal;

multiplying the error amplified signal with the rectified signal to generate an arithmetical signal;

comparing the arithmetical signal with the sense signal to generate a reset signal;

detecting a current flowing through the energy storage component to generate a zero current signal as a set signal; and

generating the switching signal based on the reset signal and the set signal.

17. A method of modulating current flowing through a load with a triac dimmer in a switching mode power supply, comprising:

coupling an AC input signal to a triac dimmer, to modify the AC input signal with a target phase angle to generate a shaped AC signal;

rectifying the shaped AC signal to generate a rectified signal;

filtering the rectified signal to generate a filtered signal;

coupling the filtered signal to a DC/DC converter to provide power to a load, wherein the DC/DC converter has a main switch operating in the ON and OFF states;

comparing the rectified signal with a constant reference signal to generate a dimming signal;

generating a feedback signal indicative of the power supplied to the load; and

generating a switching signal in response to the dimming signal and the feedback signal to control the main switch.

18. The method of claim 17, wherein the step of generating a switching signal in response to the dimming signal and the feedback signal comprises:

generating an oscillation signal by an oscillator as a set signal;

amplifying the difference between the dimming signal and the feedback signal to generate an error amplified signal;

generating a reset signal in response to the error amplified signal and the set signal by an on-time controller; and

generating a switching signal in response to the set signal and the reset signal.

19. The method of claim 17, wherein the step of generating a switching signal in response to the dimming signal and the feedback signal comprises:

detecting a current flowing through the energy storage component to generate a zero current signal as a set signal;

amplifying the difference between the dimming signal and the feedback signal to generate an error amplified signal;

generating a reset signal in response to the error amplified signal and the set signal by an on-time controller; and

generating a switching signal in response to the set signal and the reset signal.