LED control unit, lighting device having the same, and operating method thereof
A light-emitting diode (LED) control unit includes: a pulse generator configured to generate a pulse signal; a T-filter configured to convert the pulse signal into a triangular wave signal; a first gate driver configured to receive the triangular wave signal and output a first gate control signal; a second gate driver configured to receive the first gate control signal and output a second gate control signal; a first switch configured to turn on a first LED string corresponding to a first color temperature based on the first gate control signal; a second switch configured to turn on a second LED string corresponding to a second color temperature based on the second gate control signal; and a power supply circuit configured to supply a power supply voltage to the pulse generator, the first gate driver, and the second gate driver by stepping down an operating voltage of the LED driver.
1 . A light-emitting diode (LED) control unit comprising:
a pulse generator configured to generate a pulse signal;
a T-filter configured to convert the pulse signal into a triangular wave signal;
a first gate driver configured to receive the triangular wave signal and output a first gate control signal;
a second gate driver configured to receive the first gate control signal and output a second gate control signal;
a first switch configured to turn on a first LED string corresponding to a first color temperature based on the first gate control signal;
a second switch configured to turn on a second LED string corresponding to a second color temperature based on the second gate control signal; and
a power supply circuit configured to supply a power supply voltage to the pulse generator, the first gate driver, and the second gate driver by stepping down an operating voltage of an LED driver.
2 . The LED control unit of claim 1 , wherein the first color temperature is higher than the second color temperature.
3 . The LED control unit of claim 1 , wherein the pulse generator comprises:
a first resistor;
a first capacitor connected between a first terminal of the first resistor and a ground terminal; and
a first Schmitt trigger inverter connected to the first terminal of the first resistor and a second terminal of the first resistor.
4 . The LED control unit of claim 3 , wherein the T-filter comprises:
a second resistor having a first terminal connected to the second terminal of the first resistor;
a third resistor connected to a second terminal of the second resistor; and
a second capacitor connected between the second terminal of the second resistor and the ground terminal.
5 . The LED control unit of claim 4 , wherein a resistance of the third resistor is varied to control a time to reach a trigger level of the first Schmitt trigger inverter.
6 . The LED control unit of claim 3 , wherein the T-filter comprises:
a second resistor having a first terminal connected to the second terminal of the first resistor;
a selection switch configured to connect one of a plurality of resistors to a second terminal of the second resistor to control a time to reach a trigger level of the first Schmitt trigger inverter; and
a second capacitor connected between the second terminal of the second resistor and the ground terminal.
7 . The LED control unit of claim 3 , wherein the first gate driver comprises a second Schmitt trigger inverter configured to receive an output signal of the T-filter and output the first gate control signal, and
the second gate driver comprises a third Schmitt trigger inverter configured to receive the first gate control signal and output the second gate control signal.
8 . The LED control unit of claim 1 , wherein the first switch is between a first cathode terminal of the first LED string and a ground terminal, and
the second switch is between a second cathode terminal of the second LED string and the ground terminal.
9 . The LED control unit of claim 1 , wherein the power supply circuit comprises:
a first regulator configured to receive the operating voltage and output a first voltage;
a second regulator configured to receive an output voltage of the first regulator and output the power supply voltage; and
a bypass control circuit configured to determine whether to bypass the first regulator according to a level of the operating voltage.
10 . The LED control unit of claim 9 , wherein the bypass control circuit is configured to:
activate the first regulator based on the operating voltage being greater than or equal to a reference voltage,
deactivate the first regulator based on the operating voltage being less than the reference voltage, and
input the operating voltage to the second regulator.
11 . A lighting device comprising:
a light-emitting diode (LED) module configured to:
receive an operating voltage, and
output light of different color temperatures;
an LED control unit configured to:
receive the operating voltage, and
control color temperature or dimming of the LED module; and
an LED driver configured to:
receive AC power, and
provide the operating voltage to the LED module and the LED control unit,
wherein the LED control unit comprises a power supply circuit, the power supply circuit comprising a first regulator and a second regulator, the operating voltage being an input to the first regulator and the second regulator, and the power supply circuit being configured to distribute a power lost as heat between the first regulator and the second regulator.
12 . The lighting device of claim 11 , wherein the LED module comprises:
a first LED string configured to output light of a first color temperature; and
a second LED string configured to output light of a second color temperature that is lower than the first color temperature.
13 . The lighting device of claim 11 , wherein the LED control unit comprises:
a pulse generator configured to:
receive the operating voltage, and
output a pulse signal;
a T-filter configured to:
receive the pulse signal, and
output a triangular wave signal;
at least one gate driver configured to:
receive the triangular wave signal, and
output a gate control signal; and
at least one switch configured to:
receive the gate control signal, and
switch the LED module.
14 . The lighting device of claim 11 , wherein the LED control unit comprises:
a pulse generator configured to:
receive the operating voltage, and
output a pulse signal;
a low-pass filter configured to:
receive the pulse signal, and
convert the pulse signal into a DC voltage in a form of a triangular wave;
a comparator configured to compare an output voltage of the low-pass filter with a reference voltage;
at least one gate driver configured to:
receive an output signal of the comparator, and
output a gate control signal having a duty ratio according to the reference voltage; and
at least one switch configured to:
receive the gate control signal, and
switch the LED module.
15 . The lighting device of claim 14 , wherein the comparator comprises:
an operational amplifier;
a resistor connected between a non-inverting terminal of the operational amplifier and an output terminal of the operational amplifier; and
a selection switch configured to determine the duty ratio by connecting one of a plurality of resistors between an inverting terminal of the operational amplifier and a ground terminal.
16 . A method of operating a light-emitting diode (LED) control unit, the method comprising:
receiving an operating voltage from an LED driver;
generating a power supply voltage from the operating voltage using a first regulator and a second regulator;
distributing a power lost as heat between the first regulator and the second regulator;
adjusting a pulse width modulation (PWM) duty ratio through control of a selection switch; and
controlling a color temperature or a dimming of an LED module according to the PWM duty ratio,
wherein the controlling of the color temperature or the dimming comprises:
turning on a first LED string corresponding to a first color temperature in response to a first gate control signal having the PWM duty ratio; and
turning on a second LED string corresponding to a second color temperature lower than the first color temperature in response to a second gate control signal having the PWM duty ratio.
17 . The method of claim 16 , further comprising:
generating a pulse signal using a Schmitt trigger inverter based on a time constant value corresponding to a resistor and a capacitor; and
converting the pulse signal into a triangular wave signal.
18 . The method of claim 17 , wherein the adjusting of the PWM duty ratio comprises controlling a time to reach a trigger level of the Schmitt trigger inverter.
19 . The method of claim 18 , wherein the adjusting of the PWM duty ratio further comprises varying the time constant value, wherein the time constant value is associated with a T-filter, and the time constant value determines a slope of the triangular wave signal.