Method and apparatus for precise temperature brightness compensation of LED

摘要

The invention is a method and apparatus to provide a temperature compensation for LED brightness utilizing temperature dependence of voltage-current characteristic of the LED. Methods ensure the precise compensation of brightness of LED using two or more temperatures to tune an LED driver circuit without the use of thermistors or other temperature sensor.;This method also allows for circuits that compensate brightness not only of a single LED but of an assembly of LEDs. The method allows to manufacture LED modules with built-in temperature brightness compensation circuit. These modules can be used in a variety of illuminating equipment including but not limited to home lights, vehicle turn or brake signals, traffic lights, and a backlight for LCD display.

主权项

1. A method of compensation of brightness of the LED or the assembly of LED, ensure the precise compensation at least at three temperatures, comprising the steps of:
a. Dividing the temperature operating range of the LED or the assembly of LEDs into two temperature intervals, from a high to middle temperature, and from the middle to low temperature; b. Finding a first optimal voltage and first optimal resistance for temperature interval from high to middle temperatures by:
1) Placing an LED assembly into a temperature-controlled container with a window;2) Connecting the LED assembly to an adjustable power supply unit with a voltmeter across the LED assembly, and an ammeter in series with the LED assembly;3) Directing the LED assembly to a light meter through the output window of the temperature-controlled container;4) Setting a high working temperature in the temperature-controlled container;5) Adjusting the power supply unit so that the light meter reads the required brightness of the LED assembly;6) Recording the current and the forward voltage of the LED assembly at the high temperature setting;7) Setting a low working temperature in the temperature-controlled container;8) Adjusting the adjustable power supply so that the light meter reads the same brightness as it did when the container was at the previous high temperature setting;9) Recording the current and the forward voltage of the LED assembly at the low temperature setting necessary to achieve the same brightness measured at the high temperature setting10) Plotting the currents and voltages recorded at the high and low temperatures on a two-dimensional current-voltage graph;11) Connecting the graph points of the high and low temperature results with a straight line until it crosses the current and the voltage axes;12) Using the voltage intercept point on the graph as the optimal voltage value of source for supply of the LED or the assembly of LEDs for consistent brightness; and13) Using the ratio of the intercept voltage value to the intercept current value as the value of the optimal resistance of the resistor for supply of the LED assembly c. Finding a second optimal voltage and second optimal resistance for temperature from middle to low temperature by repeating the method described by 1) through 13) listed above in step b d. Recording the value of the forward voltage of the LED or the assembly of LEDs at a middle temperature; e. Connecting the LED or the assembly of LEDs to the power supply set at the first optimal voltage output through a resistor with the first optimal resistance, and increasing the temperature of the LED or the assembly of LEDs, recording the forward voltage when the LED is at the middle temperature as the temperature is increased; f. With a decreasing temperature and increasing voltage of the LED or the assembly of LED equal or more than recorded forward voltage on middle temperature connect the LED or the assembly of LED to the power supply with second optimal voltage through resistor with second optimal resistance.