LED driving circuit, LED device comprising the same, and driving method of LED

Patent metadata

Field	Value
Publication number	US-10104728-B2
Application number	US-201615380254-A
Country	US
Kind code	B2
Filing date	Dec 15, 2016
Priority date	Dec 18, 2015
Publication date	Oct 16, 2018
Grant date	Oct 16, 2018

Abstract

A light emitting diode (LED) driving circuit disclosed herein controls a switching operation of a power switch connected to an LED string and includes a reference voltage generator configured to generate a frequency modulation reference voltage according to a dimming signal that controls brightness of the LED string, and a switching controller configured to control a switching frequency of the power switch to be constant when a level of the dimming signal is higher than that of the frequency modulation reference voltage, and control the switching frequency of the power switch based on the dimming signal when a level of the dimming signal is lower than that of the frequency modulation reference voltage.

First claim

What is claimed is:

1. A light emitting diode (LED) driving circuit for controlling a switching operation of a power switch connected to an LED string, comprising:
a reference voltage generator configured to generate a frequency modulation reference voltage according to a dimming signal that controls brightness of the LED string; and
a switching controller configured to control a switching frequency of the power switch to be constant when a level of the dimming signal is higher than that of the frequency modulation reference voltage, and vary the switching frequency of the power switch based on the dimming signal when a level of the dimming signal is lower than that of the frequency modulation reference voltage.

2. The LED driving circuit of claim 1 , wherein the switching controller is configured to generate a compensation dimming signal so as to control a delay period according to the dimming signal, and control a turn-on time of the power switch on the basis of a comparison result between a level of the compensation dimming signal and that of the frequency modulation reference voltage when a level of the dimming signal is lower than that of the frequency modulation reference voltage.

3. The LED driving circuit of claim 2 , wherein the reference voltage generator is configured to generate an upper limit reference voltage and a lower limit reference voltage, and
the switching controller generates a modulation control signal on the basis of comparison results between a sensing voltage, which corresponds to a current flowing at the LED string, and each of the upper limit reference voltage and the lower limit reference voltage, and the compensation dimming signal by adding a compensation signal, which is generated according to the modulation control signal, to the dimming signal.

4. The LED driving circuit of claim 3 , wherein the switching controller includes:
a first comparator configured to compare the sensing voltage with the upper limit reference voltage;
a second comparator configured to compare the sensing voltage with the lower limit reference voltage; and
a set-reset (SR) flip-flop configured to generate the modulation control signal according to outputs of the first comparator and the second comparator.

5. The LED driving circuit of claim 3 , wherein the switching controller includes a delay controller configured to generate the compensation signal, which is being increased during a period from a time at which the sensing voltage reaches the lower limit reference voltage to a time at which the sensing voltage reaches the upper limit reference voltage, according to the modulation control signal, and the compensation dimming signal by adding the compensation signal and the dimming signal.

6. The LED driving circuit of claim 5 , wherein the delay controller includes:
a current source;
an amplifier including a first input terminal to which the dimming signal is input, a second input terminal, and an output terminal connected to the second input terminal;
a first switch connected between the output terminal of the amplifier and a first node, and configured to perform a switching operation according to the modulation control signal; and
a capacitor connected between the first node and the output terminal of the amplifier,
wherein the compensation dimming signal depends on a voltage at the first node.

7. The LED driving circuit of claim 6 , wherein the delay controller further includes a second switch connected between the current source and the first node, and configured to perform a switching operation according to the modulation control signal.

8. The LED driving circuit of claim 3 , wherein the switching controller includes:
a comparator configured to compare the compensation dimming signal with the frequency modulation reference voltage, thereby generating a frequency control signal, and
a logical operator configured to perform a logical operation on the frequency control signal and the modulation control signal, thereby generating a gate control signal.

9. A light emitting diode (LED) device comprising:
an LED string;
a power switch electrically connected to the LED string, and configured to control a current flowing at the LED string; and
an LED driving circuit configured to generate a frequency modulation reference voltage according to a dimming signal that controls brightness of the LED string, generate a compensation dimming signal so as to control a delay period according to the dimming signal, and vary a switching frequency of the power switch on the basis of a comparison result between a level of the compensation dimming signal and that of the frequency modulation reference voltage when a level of the dimming signal is lower than that of the frequency modulation reference voltage.

10. The LED device of claim 9 , wherein the LED driving circuit includes:
a reference voltage generator configured to generate an upper limit reference voltage, a lower limit reference voltage, and the frequency modulation reference voltage according to the dimming signal; and
a switching controller configured to generate a compensation dimming signal by adding a compensation signal to the dimming signal, and control a turn-on time of the power switch in synchronization with a time at which a level of the compensation dimming signal reaches the level of the frequency modulation reference voltage when the level of the dimming signal is lower than the level of the frequency modulation reference voltage.

11. The LED device of claim 10 , wherein the switching controller generates a modulation control signal on the basis of comparison results between a sensing voltage, which corresponds to the current flowing at the LED string, and each of the upper limit reference voltage and the lower limit reference voltage, and generates the compensation signal that is generated according to the modulation control signal.

12. The LED device of claim 11 , wherein the switching controller includes:
a first comparator configured to compare the sensing voltage with the upper limit reference voltage;
a second comparator configured to compare the sensing voltage with the lower limit reference voltage; and
a set-reset (SR) flip-flop configured to generate the modulation control signal according to outputs of the first comparator and the second comparator.

13. The LED device of claim 11 , wherein the switching controller includes a delay controller configured to generate the compensation signal, which is being increased during a period from a time at which the sensing voltage reaches the lower limit reference voltage to a time at which the sensing voltage reaches the upper limit reference voltage, according to the modulation control signal, and the compensation dimming signal by adding the compensation signal and the dimming signal.

14. The LED device of claim 13 , wherein the delay controller includes:
a current source;
an amplifier including a first input terminal to which the dimming signal is input, a second input terminal, and an output terminal connected to the second input terminal;
a first switch connected between the output terminal of the amplifier and a first node, and configured to perform a switching operation according to the modulation control signal; and
a capacitor connected between the first node and the output terminal of the amplifier,
wherein the compensation dimming signal depends on a voltage at the first node.

15. The LED device of claim 14 , wherein the delay controller further includes a second switch connected between the current source and the first node, and configured to perform a switching op

Assignees

• Fairchild Korea Semiconductor Ltd
• Semiconductor Components Ind Llc

Inventors

• Lee Minwoo
• Song Moonsik
• Yang Seunguk

Classifications

• H05B45/48

  having LEDs organised in strings and incorporating parallel shunting devices · CPC title

• H05B33/0815 Primary

  Electricity · mapped topic

• H05B33/0845

  Electricity · mapped topic

• H05B33/083

  Electricity · mapped topic

• H05B45/10 Primary

  Controlling the intensity of the light · CPC title