White LED driver and application of detailed interpretation and analysis

In order to keep the white LED lighting level can not only get good application, and can achieve high efficiency, the first is to make it meet the application conditions, the second is the need to adopt appropriate to the driver circuit to meet the parameters of the LDE with requirements. A application requirements,

1, the drive circuit is a specially designed for LED power supply, special power supply, to has a simple circuit structure, small footprint, volume and higher conversion efficiency.

2, drive circuit, the output of the electric parameters ( Current, voltage) To match the driven LED technology parameters, meet the requirements of the LED, and has a high precision of constant current control, appropriate pressure limiting function. Multiplexed output, the output of each all the way to be able to separate control.

3, have good linearity dimming function, in order to meet the different applications of LED brightness control requirements.

4, the abnormal state ( LED open circuit, short circuit, drive circuit fault) , the circuit of circuit itself, LED and the user has a corresponding protection.

5, driver circuit to work, to interfere with the normal work of the other circuit, meet the requirement of electromagnetic compatibility.

2, linear drive application linear drive application is one of the most simple and most direct drive applications. In white LED lighting level application, although there are some problems such as low efficiency and poor regulatory, but because of its simple circuit, small size, can satisfy the general requirements and therefore widely applied in certain occasions.

1, regulated power supply, Vdd is shown in figure 1 + ballast resistance R way to drive mode, regulated power supply + ballast resistor circuit has the advantage of simple structure, low cost. With LED in series on the resistance of the additional loss is bigger, and linear regulated power supply Vdd its power consumption is bigger also, so the combination together to get the overall efficiency is low (

2, current Vdd + ballast resistance R + electronic switch S way: figure 2 shows the improvement of driving mode is figure 3 drive way, its advantage is not only to improve the control precision of the LED current, and the brightness of the LED can also be through changing the on and off of electronic switch S ratios. However, because of series resistance and the additional loss of the linear current regulator was high, the overall efficiency is still very low, so get concrete application scope is limited by the larger.

3, type switch drive applications

type switch drive can be used to obtain good current control precision and high overall efficiency, switch mode driver.

applications mainly divided into two major categories of depressurization and booster.

1, step-down switch drive mode: step-down switch drive for power supply voltage of the voltage is higher than that of the LED or the application of multiple LED driven by parallel circumstances.

the main principle of the circuit is used in accordance with the requirements on and off of electronic switch S of chopping current, lf could satisfy the requirement of LED is working to get the current value, through the role of the feedback current ( Current sampling by R0) Leds for the current If stable in a certain range, and at the same time can have certain dimming function. Figure, inductance L is a S opening energy storage and S pass the break of stream function, to reduce the flow through the LED current If the volatility. 2, the booster type switch drive booster type switch drive for power supply voltage is lower than the voltage of the leds or LED driven by series connection of multiple applications.

working principle is to use on and off in accordance with the requirements of the circuit of the electronic switch S on-off action. In S opening Vdd power supply for the inductive energy storage, L S pass final L the voltage polarity reversal, and power supply voltage of the Vf superposition could satisfy the requirement of LED is working to get the current value If and voltage Vr, through the current negative feedback effect ( Current sampling by R0) Current through the LED, If stable in a certain range, at the same time can have a range of dimming function.

4, dimming applications

white LED lighting level is not suitable for using linear hand period of to adjust the brightness of the light changes, current should be used If the amplitude of the same ( The working current of LED) , only change the If, per unit time of current pulse width in the j to move light, because it will not change its luminescence spectrum caused by partial color of white light. Commonly used dimming applications mainly adopts the following several ways: 1, pulse width modulation mode: pulse width modulation is a common way of adjusting LED brightness. By changing on the LED on the width of the rectangular pulse current is big, the LED on the average current changes in a larger scope, large range of dimming effect can be obtained.

2, frequency modulation way: frequency modulation is another a way to adjust the LED brightness. Keep on the LED on the rectangular pulse current ( Amplitude unchanged) The width of the constant, by changing the unit of time in the LED on the rectangular pulse; In the current number of how many, the LED on the average current over a wide range of change, make the LED brightness has a wide range of adjustment.

3, position Angle modulation way: an Angle modulation is to use a string containing the binary sequence pulse, and sequence of each width of pulse extend according to the proportion of its value. By changing the unit time on the LED on the rectangular pulse; The width of the current has a value of extension, the LED on the average current over a wide range of change, to adjust the brightness of LED.

all in all, white LED lighting level is a kind of lighting can be used to replace ordinary high-power solid light-emitting devices, though subject to current prices, to some extent, restricted the application of speed, but since it has the good performance, with the progress of research and development technology, can predict white LED lighting level must have a good application prospect.