In order to ensure that the lighting level of white LED can not only get a good application, and can get a higher efficiency, the first need to make it meet certain application conditions, White Light Illuminator followed by the need to use the appropriate drive circuit to meet the LDE work parameters with the requirements The
Drive circuit is a special power supply for the LED, White Light Illuminator to have a simple circuit structure, a smaller footprint, and higher conversion efficiency.
B. The output electrical parameters (current, voltage) of the drive circuit are matched with the technical parameters of the driven LED to meet the requirements of the LED and have a high accuracy constant current control and a suitable voltage limiting function. Multiple output, White Light Illuminator each way the output should be able to separate control.
C. With a good linearity dimming function to meet the different applications on the LED light brightness adjustment requirements.
D. In the abnormal state (LED open circuit, short circuit, White Light Illuminator drive circuit failure), the circuit can circuit itself, LED and the user has a corresponding protective effect.
E. Drive circuit work, the other circuit of the normal work of less interference to meet the relevant electromagnetic compatibility requirements.
Linear drive applications are one of the simplest and most direct driver applications. White Light Illuminator In the lighting-grade white LED applications, although there are low efficiency, poor regulation and other issues, but because of its simple circuit, small size, to meet the general requirements, so in some specific occasions, more applications.
A. Power supply Vdd + ballast resistance R way for the regulator power supply + ballast resistance drive mode, the circuit has the advantage of simple structure, low cost. White Light Illuminator The additional losses on the resistors in series with the LEDs are large and the power consumption of the linearly regulated power supply Vdd itself is also large, so that the overall efficiency of the two is too low (<50%), and the LED current Control accuracy is low, brightness can not be adjusted, it is generally only used in smaller power, White Light Illuminator short time lighting occasions, such as LED flashlight, emergency lighting.
B. Steady flow power supply Vdd + ballast resistance R + electronic switch S mode: its advantages not only improve the LED current control accuracy, White Light Illuminator and LED brightness can also change the electronic switch S to adjust the ratio. However, due to the higher resistance of series resistance and linear steady current power supply, White Light Illuminator the overall efficiency obtained is still very low, and the specific application range is limited.
Lighting level white LED is not suitable for the use of linear hand to change the section to adjust the brightness of its luminous, should use the current If the amplitude of the same (LED current), only change If, the unit time within the current pulse j width of the way Dimming, because it does not change its luminous spectrum and cause white light color cast. Commonly used dimming applications mainly in the following ways:
Pulse width modulation: pulse width modulation is a common way to adjust the brightness of the LED. By changing the width of the rectangular pulse current applied to the LED, White Light Illuminator the average current obtained on the LED is changed in a large range, and a large range of dimming effect can be obtained.
B. Frequency Modulation: Frequency modulation is another way to adjust the brightness of the LED. Keep the width of the rectangular pulse current (amplitude unchanged) on the LED unchanged, White Light Illuminator by changing the unit time plus the rectangular pulse on the LED; the number of current in the LED so that the average current obtained in the larger Range changes, making the LED brightness with a wide range of adjustment.
C. Bit angle modulation: Bit angle modulation is a string containing binary sequence pulses, and each bit width of the sequence pulse is extended in proportion to its bit value. White Light Illuminator By changing the unit time added to the LED on the rectangular pulse; White Light Illuminator in the current occupied by the value of the width of the extension, so that the LED on the average current in a large range of changes in order to adjust the brightness of the LED.