Circuit And Method For Driving A Light-Emitting Diode

• US 20130249440A1
• Filed: 11/29/2012
• Published: 09/26/2013
• Est. Priority Date: 03/23/2012
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Doshi, Montu Virendra, Barrow, Steven Michael
• Granted Patent: US 9,736,898 B2
• Time in Patent Office: Days
• US Class Current: 315/309
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/325 Pulse-width modulation [PWM]
• CPC Class Codes: H05B 45/355 Power factor correction [PFC]; Reactive power compensation
• CPC Class Codes: H05B 45/385 using flyback topology
• CPC Class Codes: H05B 45/397 Current mirror circuits
• CPC Class Codes: H05B 47/10 Controlling the light source
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

Circuits and methods for driving an LED from a secondary side of a transformer are disclosed herein. An embodiment of the method includes monitoring an input voltage to determine the power level intended to drive the LED. The current flow through the primary side of the transformer is adjusted to make the power actually driving the LED equal to the power intended to drive the LED.

Claims

1. A method for driving an LED from a secondary side of a transformer;

the method comprising;

monitoring an input voltage to determine the power level intended to drive the LED; and

adjusting the current flow through the primary side of the transformer to make the power driving the LED equal to the power intended to drive the LED.

2. The method of claim 1, wherein the input voltage has a conduction angle associated therewith and wherein the power level intended to drive the LED is related to the conduction angle.

3. The method of claim 2 and further comprising powering the LED to a predetermined level when the conduction angle exceeds a predetermined value.

4. The method of claim 2 and further comprising powering the LED to a predetermined level when the conduction angle is less than a predetermined value.

5. The method of claim 4, wherein the predetermined level constitutes no power being delivered to the LED.

6. The method of claim 1, wherein the primary side of the transformer is driven by way of a pulse width modulated signal.

7. The method of claim 6, wherein the duty cycle of the pulse width modulated signal is related to the power on the primary side of the transformer.

8. The method of claim 7, wherein the adjusting comprises adjusting the duty cycle of the pulse width modulated signal.

9. The method of claim 1 and further comprising monitoring the voltage on the primary side of the transformer to determine if ringing occurs and not driving the primary side of the transformer during the ringing.

10. The method of claim 1 and further comprising:

monitoring the temperature of the LED; and

lowering the power to the primary side of the transformer when the temperature is above a predetermined value.

11. The method of claim 1 wherein current flow through the primary side of the transformer is a pulse width modulated signal and wherein the adjusting comprises:

multiplying the duty cycle of the pulse width modulated signal by the input voltage to yield a product;

comparing the product to a reference voltage that is representative of the power level intended to be delivered to the LED to yield an error; and

adjusting the current flow through the primary side of the transformer based on the error.

12. The method of claim 11, wherein the RMS value of the input voltage is multiplied by the duty cycle of the pulse width modulated signal.

13. A circuit for driving an LED, the circuit comprising:

a transformer having a primary side and a secondary side wherein the LED is connected to the secondary side;

an input connected to the primary side of the transformer, wherein a voltage at the input is representative of the power to be delivered to the LED;

a current regulator connected in series with the primary side of the transformer;

a control circuit that controls the current regulator based on the voltage at the input.

14. The circuit of claim 13, wherein the voltage at the input has a conduction angle associated therewith and wherein the power to be delivered to the LED is proportional to the conduction angle.

15. The circuit of claim 13, wherein the current regulator is a switch.

16. The circuit of claim 13, wherein the current regulator is controlled with a pulse width modulated signal.

17. The circuit of claim 13, wherein the control circuit monitors the power on the primary side of the transformer.

18. The circuit of claim 13 and further comprising an input that is connectable to a temperature sensor on the LED, wherein the control circuit reduces the power to the primary side of the transformer when the temperature sensor indicates that the temperature of the LED has exceeded a predetermined value.

19. The circuit of claim 13 wherein the control circuit:

drives the current regulator with a pulse width modulated signal;

multiplies the duty cycle of the pulse width modulated signal with the voltage at the input yielding a product;

compares the product to a reference voltage that is representative of the power intended to be delivered to the LED to yield an error; and

controls the current regulator based on the error.

20. A circuit for driving an LED, the circuit comprising:

a transformer having a primary side and a secondary side, the secondary side being connected to the LED, the primary side being driven by a signal having a conduction angle, wherein the conduction angle is proportional to dimming intended to applied to the LED;

wherein the primary side of the transformer is driven based on current regulation when the dimming is below a predetermined value; and

wherein the primary side of the transformer is driven based on power regulation when the dimming is greater than the predetermined value.