LED driving apparatus with temperature compensation function

Abstract

An LED driving apparatus having a temperature compensation function includes a reference voltage generator for generating a first reference voltage and a non-inversion amplification unit for performing non-inversion amplification to a difference voltage between the first reference voltage and a forward voltage with a preset gain. A driving unit adjusts a supply voltage in response to the voltage from the non-inversion amplification unit to supply the adjusted supply voltage to a light source having light emitting diodes. A forward voltage detector detects the forward voltage at an anode of the light emitting diodes of the light source to supply the forward voltage to the non-inversion amplification unit. Luminance variation can be compensated according to temperature changes by using a forward voltage of an LED light source so that the forward voltage of the LED light source can be controlled in association with a target current value of ambient temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram of a conventional LED driving apparatus;

FIG. 2 is a block diagram of an LED driving apparatus of the invention;

FIG. 3 is a circuit diagram of the current limiter shown in FIG. 2; and

FIG. 4 is a graph illustrating luminance variation-temperature characteristics of the inventive and conventional LED driving apparatuses.

Claims

1. A light emitting diode driving apparatus comprising: a reference voltage generator for generating a first reference voltage;a non-inversion amplification unit for performing non-inversion amplification to a difference voltage between the first reference voltage and a forward voltage with a preset gain;a driving unit for adjusting a supply voltage in response to the voltage from the non-inversion amplification unit to supply the adjusted supply voltage to a light source having light emitting diodes; anda forward voltage detector for detecting the forward voltage at an anode of the light emitting diodes of the light source to supply the forward voltage to the non-inversion amplification unit,whereby temperature change is compensated.

2. The light emitting diode driving apparatus according to claim 1, wherein the reference voltage generator is adapted to adjust the first reference voltage in response to user selection.

3. The light emitting diode driving apparatus according to claim 1, wherein the non-conversion amplification unit comprises a non-inversion operation amplifier, which includes: an inversion input terminal connected to a first reference voltage terminal connected from the reference voltage generator; anda non-inversion input terminal connected to a forward voltage terminal of the forward voltage detector.

4. The light emitting diode driving apparatus according to claim 3, wherein the inversion input terminal of the non-inversion amplification unit is connected to the first reference voltage terminal via a first resistor and to an output of the non-inversion operation amplifier via a second resistor, and the non-inversion input terminal of the non-inversion amplification unit is connected to the forward voltage terminal via a third resistor.

5. The light emitting diode driving apparatus according to claim 3, further comprising an on/off switch for switching connection between the non-inversion input terminal of the non-inversion amplification unit and the supply voltage terminal to turn on/off the light source.

6. The light emitting diode driving apparatus according to claim 3, further comprising a current limiter for supplies the second reference voltage in place of the output voltage to the driving unit thereby limiting the supply voltage of the driving unit if the output voltage of the non-inversion amplification unit is lower than a preset second reference voltage.

7. The light emitting diode driving apparatus according to claim 6, wherein the current limiter includes: a comparator for comparing the output voltage of the non-inversion amplification unit with the second reference voltage; anda switch for selecting a larger one of the output voltage of the non-inversion amplification unit and the second reference voltage in response to the comparison result of the comparator.

8. The light emitting diode driving apparatus according to claim 3, wherein forward voltage detector includes a buffer operation amplifier for detecting the forward voltage from an anode of the light emitting diodes of the light source to supply the forward voltage to the non-inversion amplification unit.

9. The light emitting diode driving apparatus according to claim 3, wherein the driving unit includes: a transistor having a base connected to the output terminal of the non-inversion amplification unit, an emitter connected to the supply voltage terminal via a resistor and a collector connected to the anode of the light emitting diodes of the light source;a capacitor connected to the base of the transistor and the supply voltage terminal to suppress excessive voltage from the switching of the transistor; anda diode having a cathode connected to the base of the transistor and an anode grounded.