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2016September

Several white LED driver

From: www.szbako.com Data:01/09/2016

in order to ensure that the lighting white LED can not only get good application, and can obtain higher efficiency in the use of, first of all need to meet certain application conditions, followed by the need to adopt suitable driving circuit to meet the LDE parameters with the requirements.

one, application requirements

1, drive circuit is a kind of special power supply for LED, to have a simple circuit structure, a smaller footprint, and a higher conversion efficiency. 2, the output voltage of the driving circuit (current, voltage) to match with the technical parameters of the driven LED, meet the requirements of LED, and has a high precision of constant current control, suitable for the function. Multiple outputs, each output should be able to control the output. 3, with a good linear dimming function, in order to meet the requirements of different applications on the LED luminous brightness adjustment. 4, in the abnormal state (LED open, short circuit, drive circuit fault), the circuit can be on the circuit itself, LED and users have a corresponding protective effect. 5, when the driving circuit, the normal work of other circuits less interference, to meet the relevant requirements of the electromagnetic compatibility.

two, linear drive application

linear drive application is one of the most simple and the most direct drive applications. In the application of white LED lighting level, although there are many problems such as low efficiency, poor adjustment and so on, because of its simple circuit, small size, can meet the general requirements, so in some particular applications more.

1, voltage stabilized power supply Vdd+ R mode Figure 1 for the voltage stabilized power supply + ballast resistance of the drive mode, the circuit is simple structure, low cost. In the additional loss resistor in series with the LED is larger, and the linear regulator power supply (VDD) its power consumption is large, the superposition of both together to get the overall efficiency is very low (the 50%) and low control accuracy of the LED current, brightness is adjustable, it is generally only used in small power and short time lighting applications, such as LED flashlight, emergency lights. 2, stabilized power supply Vdd+ town flow resistance R + electronic switch s way: Figure 2 shows the driving mode is figure 3 drive the improvement of the way, the utility model has the advantages of not only improves the LED current control accuracy and the brightness of the LED can also by changing the electronic switch s on-off ratio of the regulation. However, due to the additional loss of the resistance and linear regulated power supply series are high, so the overall efficiency is still very low, the specific scope of application is greatly limited.

three, switch type drive application

use switch type drive can get good current control accuracy and high overall efficiency, switch type drive.

application is mainly divided into two categories: Buck and boost.

1, buck switching drive mode: the buck switch driver is for the power supply voltage is higher than the LED of the terminal voltage or the use of multiple LED parallel driver.

circuit of the main principle is to use in accordance with the requirements of the on-off electronic s the chopping current switch, come to meet such requirements of current lf values, by the current negative feedback (by R0 of current sampling) that passes over a LED current if stable within a certain scope. At the same time, it can be both a dimming function. The inductance L is to s open energy storage and s to turn off the rear of freewheeling role, to reduce the fluctuation of flows through the LED current if. 2, the boost switch driver is for the power supply voltage is lower than the LED of the terminal voltage or the use of multiple LED series driver. The working principle of the

circuit is to use the on-off action of the electronic switch S which is required to be switched off. In s opening power supply (VDD) to inductance L storage can, s turn off the rear l voltage polarity reversal and supply voltage VF overlapped Calais meet such requirements of current value if and voltage value VR and through the current negative feedback, current sampling by R0, the flowing through the LED current if stable within a certain range, at the same time, it can be both a range of dimming function.

4, adjusting light application way

2, frequency modulation: frequency modulation is another way to adjust the brightness of LED. Keep plus in the LED on the rectangular pulse current (constant amplitude) of width unchanged, by changing the time unit and a rectangular pulse in the LED; current of a number, the average current is led to change in a large range, makes the LED brightness with a wide range of adjustment.

3, bit angle modulation: bit angle modulation is the use of a series of pulses containing a binary sequence, and the sequence of pulses per bit width in accordance with the proportion of the value of the value to extend. By changing the unit time plus the rectangular pulse on the LED; the value of the current occupies the width of the LED, so that the average current in the larger range of change, to adjust the brightness of LED.

in short, white LED lighting is a which can be used to replace general lighting of high power solid-state light-emitting device, although subject to the current price, in a certain extent restricts the application of speed, but because of the necessity of its excellent performance, along with the continuous progress of technology research and development can predicted grade lighting white LED, it must have good application prospects.

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