LOSSLESS PRELOAD FOR LED DRIVER WITH EXTENDED DIMMING

• US 20140265898A1
• Filed: 03/15/2013
• Published: 09/18/2014
• Est. Priority Date: 03/15/2013
• Status: Abandoned Application

• Current Assignee: Power Integrations Incorporated
• Original Assignee: Power Integrations Incorporated
• Inventors: ESPINO, Marvin Cruz, DEL CARMEN, Jose R. Jr.
• Application Number:
  US13/844,356
• Publication Number:
  US 20140265898A1
• Time in Patent Office: Days
• US Class Current: 315/200.R
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/31 Phase-control circuits
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: H05B 45/59 for reducing or suppressing flicker or glow effects
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A quasi-phase active preload circuit to be coupled at the output of a non-isolated LED driver converter having a pre-stage phase-angle control dimmer circuit, such as a commonly used leading-edge control Triac dimmer, is disclosed. The quasi-phase active preload circuit may include a preload resistor coupled to a current-controlled current source configured to draw a sinking current through the preload resistor based on a peak detect signal. The peak detect signal may be, in one example, representative of a leading-edge peak voltage of an output of the Triac dimmer circuit, which may be representative of a conduction angle of the Triac dimmer circuit. During normal operating conditions, no sinking current is drawn through the preload resistor. During low dimming conditions, a sinking current that is responsive to the peak detect signal is drawn through the preload resistor. During deep dimming or when used with a leaky Triac dimmer, a maximum sinking current may be drawn through the preload resistor by the current-controlled current source.

Claims

1. An active preload circuit configured to be coupled to an output of a non-isolated light-emitting diode (LED) driver converter having a phase-angle control dimmer circuit, the active preload circuit comprising:

a preload resistor coupled to the output of the non-isolated LED driver converter; and

a current-controlled current source coupled to receive a peak detect signal representative of a conduction angle of the phase-angle control dimmer circuit, wherein the current-controlled current source is configured to draw a variable sinking current through the preload resistor, and wherein a value of the sinking current is based on the peak detect signal.

2. The active preload circuit of claim 1, wherein the phase-angle control dimmer circuit comprises a leading edge control Triac dimmer.

3. The active preload circuit of claim 1, wherein the peak detect signal is representative of a leading-edge peak voltage of an output of the phase-angle control dimmer circuit.

4. The active preload circuit of claim 1, wherein when the peak detect signal is above an upper threshold value, a switching device of the current-controlled current source is configured to be in an OFF state operating in an open circuit mode to cause a value of the sinking current to be substantially zero.

5. The active preload circuit of claim 4, wherein the upper threshold value corresponds to an upper threshold of the conduction angle of the phase-angle control dimmer circuit.

6. The active preload circuit of claim 1, wherein when the peak detect signal is below a lower threshold value, a switching device of the current-controlled current source is configured to be in an ON state to cause a value of the sinking current to have a maximum value.

7. The active preload circuit of claim 1, wherein the current-controlled current source comprises:

a voltage-controlled current source configured to draw a compensation current proportional to a voltage of the peak detect signal; and

a switching device coupled to draw the sinking current in response to a control signal, wherein the control signal is equal to a maximum bias current minus the compensation current.

8. The active preload circuit of claim 1, wherein when the peak detect signal is between an upper threshold value and a lower threshold value, a switching device of the current-controlled current source is configured to operate in a linear mode in response to the peak detect signal.

9. The active preload circuit of claim 1, wherein the current-controlled current source comprises a Darlington combination of a first BJT transistor and a second BJT transistor, and wherein the first BJT transistor is configured to draw the sinking current through the preload resistor.

10. The active preload circuit of claim 9, wherein the Darlington combination of the first BJT transistor and the second BJT transistor is controlled by a control current, and wherein the control current is generated by a voltage-controlled current source that is controlled by a scaled version of the peak detect signal.

11. The active preload circuit of claim 1, wherein the variable sinking current has a minimum value of zero amperes.

12. The active preload circuit of claim 1, wherein the current-controlled current source is coupled to receive the peak detect signal from a peak detector circuit, the peak detector circuit comprising:

a capacitor coupled to a first output terminal of the phase-angle control dimmer circuit;

a diode coupled between the capacitor and a second output terminal of the phase-angle control dimmer circuit; and

a resistor coupled between the capacitor and the second output terminal of the phase-angle control dimmer circuit.

13. The active preload circuit of claim 1, wherein the non-isolated LED driver converter is a Buck-Boost converter.

14. The active preload circuit of claim 1, wherein the non-isolated LED driver converter is a Buck or Tapped Buck converter, and wherein a Buck switch or a Buck inductor of the non-isolated LED driver converter generates a level difference between an input return and an output return of the non-isolated LED driver converter.

15. A light-emitting diode (LED) driver comprising:

a phase-angle control dimmer circuit coupled to receive an input voltage and output a phase-adjusted voltage;

a rectifier circuit coupled to receive the phase-adjusted voltage and output a rectified voltage;

a peak detector circuit coupled to receive the rectified voltage and generate a peak detect signal representative of a conduction angle of the phase-angle control dimmer circuit;

a non-isolated converter coupled to receive the rectified voltage and output an output voltage;

an active preload circuit coupled to an output of the non-isolated converter, wherein the active preload circuit comprises;

a preload resistor coupled to the output of the non-isolated converter; and

a current-controlled current source coupled to receive the peak detect signal from the peak detector circuit, wherein the current-controlled current source is configured to draw a variable sinking current through the preload resistor, and wherein a value of the sinking current is based on the peak detect signal.

16. The LED driver of claim 15, wherein the phase-angle control dimmer circuit comprises a Triac dimmer.

17. The LED driver of claim 15, wherein the peak detect signal is representative of a leading-edge peak voltage of the phase-adjusted voltage.

18. The LED driver of claim 15, wherein when the peak detect signal is above an upper threshold value, a switching device of the current-controlled current source is configured to be in an OFF state operating in an open circuit mode to cause the sinking current to have a substantially zero value.

19. The LED driver of claim 15, wherein when the peak detect signal is below a lower threshold value, a switching device of the current-controlled current source is configured to be in an ON state operating in a short circuit mode to cause the value of the sinking current to be a maximum value.

20. The LED driver of claim 15, wherein when the peak detect signal is between an upper threshold value and a lower threshold value, a switching device of the current-controlled current source is configured to operate in a linear mode in response to the peak detect signal.

21. The LED driver of claim 15, wherein the current-controlled current source comprises a Darlington combination of a first BJT transistor and a second BJT transistor, and wherein the first BJT transistor is configured to draw the sinking current through the preload resistor.

22. The LED driver of claim 15, wherein the peak detector circuit comprises:

a capacitor coupled to a first output terminal of the phase-angle control dimmer circuit;

a diode coupled between the capacitor and a second output terminal of the phase-angle control dimmer circuit; and

a resistor coupled between the capacitor and the second output terminal of the phase-angle control dimmer circuit.

23. The LED driver of claim 15, wherein the non-isolated converter is a Buck-Boost converter.

24. The LED driver of claim 15, wherein the non-isolated converter is a Buck or Tapped Buck converter, and wherein a Buck switch or a Buck inductor of the non-isolated converter generates a level difference between an input return and an output return of the LED driver.

25. The LED driver of claim 15, wherein the current-controlled current source comprises:

a voltage-controlled current source configured to draw a compensation current proportional to a voltage of the peak detect signal; and

a switching device coupled to draw the sinking current in response to a control signal, wherein the control signal is equal to a maximum bias current minus the compensation current.