Circuit for controlling LED with temperature compensation
View Patent ↗A circuit for controlling an LED with temperature compensation is employed in the LED-based system. The circuit of the invention linearly controls luminance and color of the LED according to temperature change and more precisely compensates for temperature-related variations in LED properties. Also, the circuit saves the cost of the product due to no requirement of a microprocessor. In the circuit, a waveform generator generates a sawtooth wave for Pulse Width Modulation (PWM) control. A temperature detector detects a voltage via a resistance value which is linearly variable according to changes in an ambient temperature. A PWM controller compares the sawtooth wave from the wave generator with the detection voltage from the temperature detector and generates a PWM voltage having a duty determined by the comparison result.
1. A circuit for controlling a Light Emitting Diode (LED) with temperature compensation comprising:
a waveform generator for generating a sawtooth wave for Pulse Width Modulation (PWM) control;
a temperature detector for detecting a voltage via a resistance value which is linearly variable according to changes in an ambient temperature; and
a PWM controller for comparing the sawtooth wave from the wave generator with the detection voltage from the temperature detector and generating a PWM voltage having a duty determined by the comparison result,
wherein the temperature detector comprises:
a temperature detection circuit for dividing a dimming voltage via the variable resistance value to output the detection voltage; and
a comparator for outputting a difference voltage between the detection voltage from the temperature detection circuit and the dimming voltage.
2. The circuit according to claim 1 , further comprising a driver for driving an LED backlight in response to the PWM voltage from the PWM controller.
3. The circuit according to claim 1 , wherein the temperature detection circuit comprises:
first and second resistors connected in series between a dimming voltage terminal and a ground terminal;
a first temperature detection device having a resistance value corresponding to an ambient temperature, the first temperature detection device connected in parallel to the first or second resistor; and
a plurality of temperature detection devices each having a resistance value corresponding to an ambient temperature, the temperature detection devices connected in parallel to the first temperature detection device and in series with one another.
4. The circuit according to claim 1 , wherein the temperature detection circuit comprises:
first and second resistors connected in series with each other between a dimming voltage terminal and a ground terminal;
a first temperature detection device having a resistance value corresponding to an ambient temperature, the first temperature detection device connected in parallel to the second resistor; and
second and third temperature detection devices each having a resistance value corresponding to an ambient temperature, the second and third temperature detection devices connected in parallel to the first temperature detection device and in series with each other.
5. The circuit according to claim 4 , wherein the comparator comprises:
an inversion input terminal for receiving the voltage detected at a connecting node of the first and second resistors;
a non-inversion input terminal for receiving the dimming voltage; and
an output terminal for outputting the difference voltage between the detection voltage from the inversion input terminal and the dimming voltage from the non-inversion input terminal.
6. The circuit according to claim 1 , wherein the temperature detection circuit comprises:
first and second resistors connected in series with each other between a dimming voltage terminal and a ground terminal;
a first temperature detection device having a resistance value corresponding to an ambient temperature, the first temperature detection device connected in parallel to the first resistor; and
second and third temperature detection devices each having a resistance value corresponding to an ambient temperature, the second and third temperature detection devices connected in parallel to the first temperature detection device and in series with each other.
7. The circuit according to claim 6 , wherein the comparator comprises:
a non-inversion input terminal for receiving the detection voltage detected at a connecting node of the first and second resistors;
an inversion input terminal for receiving the dimming voltage; and
an output terminal for outputting the difference voltage between the detected voltage from the non-inversion input terminal and the dimming voltage from the inversion input terminal.
8. The circuit according to claim 1 , wherein the PWM controller comprises:
an inversion input terminal for receiving the sawtooth wave from the waveform generator;
a non-inversion input terminal for receiving the detection voltage detected by the temperature detector; and
an output terminal for comparing the sawtooth wave from the inversion input terminal with the detection voltage from the non-inversion input terminal.