Ballast Circuit for LED-Based Lamp Including Power Factor Correction with Protective Isolation

• US 20110109230A1
• Filed: 11/11/2009
• Published: 05/12/2011
• Est. Priority Date: 11/11/2009
• Status: Active Grant

• Current Assignee: ABL IP Holding LLC (Acuity Brands, Inc.)
• Original Assignee: OSRAM Sylvania Inc. (Ams-Osram AG)
• Inventors: Simi, Victor M.
• Granted Patent: US 8,384,295 B2
• Time in Patent Office: Days
• US Class Current: 315/119
• 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 45/382 with galvanic isolation between input and output
• CPC Class Codes: H05B 45/50 responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits
• 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 ballast circuit for a light emitting diode (LED) based lamp including power factor correction with protective isolation. The circuit includes a transformer with electrically isolated windings and a power factor correction circuit that receives no feedback from a secondary winding side of the transformer. An LED-based lamp assembly and a method of driving an LED-based light source are also provided.

Claims

1. A ballast circuit to drive a light emitting diode (LED)-based light source, the ballast circuit comprising:

a rectifier circuit configured to receive an AC input voltage and provide an unregulated DC voltage;

a transformer having a primary winding coupled to the rectifier circuit, at least one secondary winding configured to be coupled to the LED-based light source, and a feedback winding, the secondary winding being electrically isolated from the primary winding and the feedback winding with no electrical path between the primary winding and the secondary winding or the feedback winding and the secondary winding;

a switch, the switch being configured to close to couple a portion of the unregulated DC voltage across the primary winding and the switch being configured to open to transfer energy from the primary winding to the secondary winding to provide a DC output voltage to drive the LED-based light source; and

a power factor correction circuit configured to control the switch in response to a first signal representative of current through the primary winding, a second signal representative of current through the feedback winding, and a third signal representative of the unregulated DC voltage, with no feedback signal coupled from the secondary winding to the controller.

2. A ballast circuit according to claim 1, the ballast circuit further comprising a switched bias circuit, the switched bias circuit comprising a bias circuit switch configured to close when the switch is open to provide a supply voltage to the power factor correction circuit.

3. A ballast circuit according to claim 2, wherein the switched bias circuit is coupled to the feedback winding, and wherein the bias circuit switch is configured to close in response to current through the feedback winding.

4. A ballast circuit according to claim 1, the ballast circuit further comprising an over-voltage protection circuit coupled to the power factor correction circuit to disable the power factor controller circuit when a voltage at the transformer exceeds a predetermined level.

5. A ballast circuit according to claim 4, wherein the over-voltage protection circuit comprises a Zener diode coupled to the feedback winding, whereby a breakdown voltage of the Zener diode is exceeded when the voltage at the transformer exceeds the predetermined level thereby disabling the power factor controller circuit.

6. A ballast circuit according to claim 4, wherein the over-voltage protection circuit comprises an over-voltage protection switch configured to close when the voltage at the transformer exceeds the predetermined level thereby disabling the power factor controller circuit.

7. A ballast circuit according to claim 1, wherein the power factor correction circuit comprises an integrated circuit power factor controller configured to receive the first signal, the second signal, and the third signal and to provide an output to control the switch.

8. A ballast circuit according to claim 1, wherein the AC input signal is a 120V AC signal.

9. An LED-based lamp assembly comprising:

a lamp housing;

a light source disposed within the lamp housing; and

a ballast disposed within the lamp housing, the ballast comprising;

a rectifier circuit configured to receive an AC input voltage and provide an unregulated DC voltage;

a transformer having a primary winding coupled to the rectifier circuit, at least one secondary winding coupled to the LED-based light source, and a feedback winding, the secondary winding being electrically isolated from the primary winding and the feedback winding with no electrical path between the primary winding and the secondary winding or the feedback winding and the secondary winding;

a switch, the switch being configured to close to couple a portion of the unregulated DC voltage across the primary winding and the switch being configured to open to transfer energy from the primary winding to the secondary winding to provide a DC output voltage to drive the LED-based light source; and

a power factor correction circuit configured to control the switch in response to a first signal representative of current through the primary winding, a second signal representative of current through the feedback winding and a third signal representative of the unregulated DC voltage, with no feedback signal coupled from the secondary winding to the controller.

10. An LED-based lamp assembly according to claim 9, the ballast circuit further comprising a switched bias circuit, the switched bias circuit comprising a bias circuit switch configured to close when the switch is open to provide a supply voltage to the power factor correction circuit.

11. An LED-based lamp assembly according to claim 10, wherein the switched bias circuit is coupled to the feedback winding, and wherein the bias circuit switch is configured to close in response to current through the feedback winding.

12. An LED-based lamp assembly according to claim 9, the ballast circuit further comprising an over-voltage protection circuit coupled to the power factor correction circuit to disable the power factor controller circuit when a voltage at the transformer exceeds a predetermined level.

13. An LED-based lamp assembly according to claim 12, wherein the over-voltage protection circuit comprises a Zener diode coupled to the feedback winding, whereby a breakdown voltage of the Zener diode is exceeded when the voltage at the transformer exceeds the predetermined level thereby disabling the power factor controller circuit.

14. An LED-based lamp assembly according to claim 12, wherein the over-voltage protection circuit comprises an over-voltage protection switch configured to close when the voltage at the transformer exceeds the predetermined level thereby disabling the power factor controller circuit.

15. An LED-based lamp assembly according to claim 9, wherein the power factor correction circuit comprises an integrated circuit power factor controller configured to receive the first signal, the second signal, and the third signal and to provide an output for controlling the switch.

16. An LED-based lamp assembly according to claim 9, wherein the AC input signal is a 120V AC signal.

17. A method of driving an LED-based light source, the method comprising:

receiving an AC input signal;

converting the AC input signal into a regulated DC output using a ballast circuit comprising;

a transformer having a primary winding, a secondary winding and a feedback winding, the secondary winding being electrically isolated from the primary winding and the feedback winding with no electrical path between the primary winding and the secondary winding or the feedback winding and the secondary winding, and

a power factor correction circuit receiving no feedback signal coupled from the secondary winding; and

coupling the regulated DC output to the LED-based light source.

18. A method according to claim 17, wherein receiving an AC input signal comprises receiving the AC input signal from a dimmer circuit.

19. A method according to claim 17, wherein converting comprises:

converting the AC input signal into a regulated DC output using a ballast circuit comprising;

a transformer having a primary winding, a secondary winding and a feedback winding, the secondary winding being electrically isolated from the primary winding and the feedback winding with no electrical path between the primary winding and the secondary winding or the feedback winding and the secondary winding, and

a power factor correction circuit receiving no feedback signal coupled from the secondary winding; and

a switched bias circuit including a bias circuit switch configured to close to provide a supply voltage to the power factor correction circuit.

20. A method according to claim 17, wherein converting comprises:

converting the AC input signal into a regulated DC output using a ballast circuit comprising;

a transformer having a primary winding, a secondary winding and a feedback winding, the secondary winding being electrically isolated from the primary winding and the feedback winding with no electrical path between the primary winding and the secondary winding or the feedback winding and the secondary winding, and

a power factor correction circuit receiving no feedback signal coupled from the secondary winding; and

an over-voltage protection circuit coupled to the power factor correction circuit to disable the power factor controller circuit when a voltage at the transformer exceeds a predetermined level.