In order to ensure lighting-class white LED light is not only able to get a good application, but also higher efficiency, first you need to make it meet certain conditions, followed by the need to adapt the drive circuit to meet the the LDE working parameters to meet them .
First, the application requirements of the LED lighting
1, the driver circuit is powered by a specifically designed for LED special power supply, to have a simple circuit configuration, a smaller occupied volume, and a high conversion efficiency.
2, the driving circuit of the output electrical parameters (current and voltage) to the technical parameters of the LED is driven match, to meet the requirements of the LED, and the constant current control with high precision, appropriate pressure limiting function. Multiple output, the output of each channel must be individually controlled.
3, with linearity better dimming function, to meet the requirements of different applications of LED brightness adjustment.
In an abnormal state (LED open circuit, short circuit, driver circuit failure), the circuit of the circuit itself, LED, and users have the appropriate protective effect.
5, when the driver circuit, the other circuit normal work interference less meet the electromagnetic compatibility requirements.
Second, the linear drive applications
The application of the linear drive is one of the most simple and most direct drive applications. Lighting-class white LED applications, although there is a low efficiency, poor regulatory issues, but because of its simple circuit, compact, to meet the general requirements, and therefore more in certain occasions.
A regulated power supply Vdd + ballast resistor R Figure 1 as a regulator power + ballast resistor drive way, the circuit has the advantage of simple structure, low cost. A resistor in series with the LED, the additional loss is larger, and the linear regulator power supply Vdd own power consumption is larger, so the two superimposed together to obtain the overall efficiency is very low (<50%), and the LED current low precision control brightness can not be adjusted, it is generally only applied to smaller power, the occasion of a short time lighting, such as LED flashlight, LED downlight, LED ceiling light, COB LED downlight, LED tube and emergency lights.
2, stable flow power source Vdd + ballast resistor R + electronic switch S manner: Figure 2 illustrated drive mode is Figure 3 drive mode of the improved manner, the advantage not only to improve the LED current control precision, but the LED brightness also can be by changing The electronic switch S off ratio to adjust. However, due to the series resistance and linear, the additional loss of the constant current power supply is higher, so the resulting overall efficiency is still low, the specific application range is more restricted.
Switching drive applications
Switch type driving good current control accuracy and a higher overall efficiency, the switched-mode driver can be obtained.
Application mode is mainly divided into the buck boost two categories.
1 buck switch driver: buck switch driver parallel drive case for the terminal voltage of the power supply voltage is higher than the LED or multiple LED.
The main principle of the circuit is the use of the chopping current obtained in accordance with the requirements off the electronic switch S, to obtain the required current lf meet LED value by the negative feedback of the current (the current sampling is by R0) so that the flows through the LED the current If is stable within a certain range, and can handle a certain dimming function. FIG inductance L of the role is played the freewheeling effect turns off in the energy storage and S S, when opened, to reduce the flow through the LED current If fluctuations. Boost switch driver Boost switch driver the tandem drive case for the power supply voltage is lower than the terminal voltage of the LED or multiple LED.
The working principle of the circuit is the use of the role in accordance with the requirements of the electronic switch S off-off. Requested when the power supply Vdd to the inductance L of the energy storage in the S, when opened, the voltage polarity is reversed on L S is turned OFF and power voltage Vf is superimposed to be met LED current value If, and the voltage value Vr, through the current negative feedback effect (the current sampling), so that the current If flowing through the LED dimming function that can handle a range of stable within a certain range, while by R0.
Dimming applications of LED light fixtures
Lighting level white LED is not suitable for a linear hand-off to change the segment to adjust the brightness of the luminous amplitude of the current If, should be used unchanged (LED working current) change only if the unit time the current pulse j width manner dimming, because it will not change its luminescence spectra caused by the white color cast. Dimming applications using the following ways: 1, pulse width modulation: pulse width modulation is a common adjust LED brightness. By changing the width of the rectangular pulse current applied to the LED on, so that the average current on the LED is changed within a larger range can be obtained a larger range of dimming effect.
2, the frequency modulation: frequency modulation is another way of adjusting LED brightness. Unchanged to maintain the width of the rectangular pulse current applied to the LED (amplitudes unchanged), a rectangular pulse applied to the LED by varying the unit time; how much the number of the current, so that the average current on the LED in the larger range changes, having a larger range of adjustment so that the LED light fixtures are more brightness.
3 bit angle modulation scheme: In angle modulation is used bunch containing a binary sequence of pulses, and each of a width of the pulse sequences in accordance with the proportion of its bit value to stretch. By changing the unit time applied to the LED on the rectangular pulse; occupy bit value of the current in extendible width, so that the average current on the LED changes within a large range, in order to adjust the LED brightness.
In short, the lighting level white LED is a solid-state light-emitting devices for high-power alternative for general lighting, although certain extent, restricted the speed of the application subject to the current price, the nature, but because it has excellent performance, with the R & D technology continues to progress, lighting-class white LEDs can be predicted and certainly has a good prospect.