Electronic Transformer Compatibility for Light Emitting Diode Systems

• US 20120112648A1
• Filed: 11/07/2011
• Published: 05/10/2012
• Est. Priority Date: 11/08/2010
• Status: Active Grant

• Current Assignee: Maxim Integrated Products, Inc. (Analog Devices, Inc.)
• Original Assignee: Maxim Integrated Products, Inc. (Analog Devices, Inc.)
• Inventors: Hariharan, Suresh
• Granted Patent: US 8,766,557 B2
• Time in Patent Office: Days
• US Class Current: 315/186
• CPC Class Codes: H02M 1/4208 Arrangements for improving power factor of AC input
• 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 45/38 using boost topology
• CPC Class Codes: H05B 45/382 with galvanic isolation between input and output
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

Various embodiments of the invention provide power factor correction in solid state lighting applications. In certain embodiments, an LED driver for an LED array is controlled for power factor correction by a control circuit block. The control circuit block comprises electronic circuitry that enables the input current to the LED driver to be measured and controlled. This control circuit block comprises at least one switching device that enables an alternating form of current at a particular frequency to be applied to the LED array regardless of whether the main power source is a DC or AC power source.

Claims

1. A sold state lighting control system that provide power factor correction, the system comprising:

a current waveform shaper coupled to receive an AC power signal, the current waveform adjusts a peak current on the AC power signal;

a bridge rectifier coupled to receive the adjusted AC power signal, the bridge rectifier converts the adjusted AC power signal to a DC power signal;

an LED driver coupled to receive the DC power signal and to generate a regulated LED power signal, the LED driver is controlled to provide power factor correction on the regulated LED power signal;

a control circuit coupled to the LED driver, the control circuit comprising at least one switching device that enables an current at a particular frequency to be applied to an LED array independent of the power signal received at the bridge rectifier; and

wherein the LED driver measures a current level on the AC power signal and controls the regulated LED power signal such that the power signal and the regulated LED power signal are in phase.

2. The system of claim 1 wherein a current level on the regulated LED power signal is controlled using a detected external voltage.

3. The system of claim 1 wherein the LED driver is configured as a direct current boost driver using a fixed frequency peak current mode control.

4. The system of claim 3 further comprising:

an inner control loop within the LED driver that provides inner peak current mode control by controlling a duty cycle of a switching MOSFET; and

an outer control loop that provides that controls the regulated LED power signal using an error amplifier.

5. The system of claim 4 wherein a current magnitude of the regulated LED power signal is adjustable by controlling a programmable reference pin on the LED driver.

6. The system of claim 1 wherein the LED driver is configured as an alternating current boost driver.

7. The system of claim 6 further comprising at least one inductor and one capacitor coupled between a rectifier bridge and the LED driver, the at least one inductor and one capacitor shaping the power signal prior to being received at the first interface.

8. The system of claim 7 wherein a current level on the power signal is controlled to be proportional to an input voltage derived at the rectifier bridge.

9. The system of claim 1 wherein the LED driver is configured as a buck-boost driver.

10. The system of claim 9 wherein a pulsating current flowing in a switching MOSFET within the LED driver is used by an inner peak control loop and an outer current control loop to control the regulated LED power signal.

11. The system of claim 9 wherein the LED driver is employed in an offline configuration to isolate an AC input on the LED driver and an LED array.

12. A method for providing power factor correction on a regulated LED power signal, the method comprising:

receiving an alternating current power signal from an electronic transformer;

shaping the power signal such that a peak current is pulled through the electronic transformer every switching cycle;

converting the alternating current power signal into a rectified direct current power signal;

controlling a switch within a driver by comparing the rectified direct current power signal to at least one reference within the driver, the switch generates a regulated LED power signal from the rectified direct current power signal; and

smoothing the regulated LED power signal to remove at least a portion of noise on the regulated LED power signal from the switch.

13. The method of claim 12 further comprising the step of filtering the rectified direct current power signal to remove at least a portion of switching noise from a bridge rectifier.

14. The method of claim 12 wherein the at least one reference within the driver is a current reference.

15. The method of claim 12 wherein the at least one reference within the driver is a voltage reference.

16. An apparatus comprising:

a current waveform shaper coupled to receive an AC power signal, the current waveform adjusts a peak current on the AC power signal;

a bridge rectifier coupled to receive the adjusted AC power signal, the bridge rectifier converts the adjusted AC power signal to a DC power signal;

a fixed frequency average mode control (FFACMC) circuit coupled to receive the DC power signal;

a programmable reference in the circuit; and

the FFACMC controlling a switch relative to a voltage on the input signal and is programmable such that a voltage drop on the input signal relative to a reference voltage results in a power factor correction (PFC) applied to an output voltage of the circuit.

17. The apparatus of claim 16 wherein the output voltage is maintained in phase with the input signal so that the circuit appears as a resistive load across the input interface.

18. The apparatus of claim 16 wherein the output voltage of the circuit is applied across a solid state lighting (SSL) device.

19. The apparatus of claim 18 wherein the solid state lighting (SSL) device comprises a light emitting diode (LED) or an array or cluster of light emitting diodes (LEDs).

20. The apparatus of claim 18 further comprising a switching device connected to the FFACMC and the solid state lighting (SSL) device to work with leading and trailing edge dimmers to provide dimming of the solid state lighting (SSL) device.