High brightness LED driver for lighting equipment

With the continuous improvement of highlighting the LED efficiency, namely the lumens per watt than increase, more and more begin to choose high brightness LED lighting applications, such as the outside of the car lights ( Daytime running lights, dipped headlights, high beam, etc. ) And general lighting equipment, etc. LED manufacturer has recently launched the efficiency of high brightness LED more than 80 lumens per watt, therefore, can make use of the LED in lighting equipment to replace the traditional halogen lamp, such as MR16 spotlights. Transition from the traditional halogen lamp to high brightness of LED can be greatly reduced power consumption, extend the service life of the product. According to market research firm Strategies Unlimited, lighting, backlighting and automotive applications will be highlighted LED the market in the main driver of growth in the next 3 to 5 years, to 2011, the market scale will reach $9 billion. Linear drive

driver HBLED best solution is to use a constant current source. Implement simple circuit of constant current source is: use a MOSFET and HBLED series, the current of HBLED testing and comparing with the reference voltage, comparing the signal feedback to the operational amplifier, thus control MOSFET gate. This circuit as an ideal current source, can be in the forward voltage, maintaining a constant current power supply voltage changes. At present, some linear driver chips, such as MAX16806, as shown in figure 1, inside the chip integrates MOSFET and high precision voltage benchmark, to maintain consistent between different lighting brightness.

are linear drive relative to switch mode the advantages: simple circuit structure, easy to implement, because there is no high frequency switch, so also do not need to consider the EMI problems. The periphery of the linear drive less component, which can effectively reduce the overall cost of the system, such as: MAX16806 required input voltage only 1 v higher than LED the total pressure drop. LED current is measured using external inspection flow resistance, thus ensuring the input voltage and the LED forward voltage changes, MAX16806 can output constant current.

linear drive power consumption is equal to the LED current multiplied by the internal ( Or external) The pressure drop of passive components. When LED current or the input voltage, power consumption will also increase, which limits the application of linear drive. In order to reduce the power consumption of lighting device, to monitor the quality of the input voltage MAX16806, if the input voltage exceeds preset values, it will reduce the drive current to reduce power consumption. The function can avoid the use of switching power supply in some applications, such as: car dome light or daytime running lights, etc. , these applications that commonly appear in abnormal high battery voltage, leading to the lights. Step-down drive

switch mode when the input voltage is much higher than the LED total pressure drop, it is best to use the switch mode step-down drive, MAX16820, for example, as shown in figure 2, it can make the power to minimize power consumption, high drive efficiency is achieved.

and driven HBLED Buck chips, MAX16820 using hysteresis control. No control loop compensation, thus simplifies the design and helps to reduce number of external components. Integrated high voltage current amplifier, able to work in the switch of up to 2 MHZ frequency, effectively reduce the circuit board space and the number of devices, as a result, MAX16820 can be ideal for the vast majority of the LED driver, for example: based on the MR16 LED, car headlights and tail lights, etc.

reduce the LED current LED brightness adjustment may reduce the LED brightness, the output spectrum will change. In some applications, such use is not recommended. In order to keep the same spectra under different brightness, had better keep current numerical prescribed by the manufacturer, then at a particular frequency or duty ratio on the output current for chopping. In order to avoid visual flicker, frequency should be higher than 100 hz. The dimming range depends on the minimum cycle LED driver is allowed.

most of the LED drive need brightness control signal generated by the microprocessor or external timers. MAX16806 MAX16831 and LED driver is 200 hz by internal control signal, used in LED brightness PWM control; Also can use external PWM signal or analog signal through the DIM pin to adjust brightness. In some applications, the introduction of the function could save the microprocessor.

choose the HB LED driver must understand specific LED lighting device, you first need to define the parameters, such as: the input voltage, voltage LED current, the LED is the guide and the change range of these parameters. Security, EMI, thermal management, mechanical properties and can take advantage of the circuit board area are also factors must be considered. Linear drive fit in with the requirements of low cost, low EMI. Type switch drive is suitable for high power, high efficiency and wide input voltage range and other applications, but the cost is higher, EMI problems must be considered. Maxim can according to different HB LED solutions to provide wide range of application.

editor: li jie