Using the constant current LED driver design high efficiency LED lighting system

With the appearance of high power LED lighting industry also faces new challenges. The service life of the LED and the power conversion efficiency of a major consideration when designing a LED lighting system. And in order to provide constant current in order to maintain the consistency of color and brightness LED, LED constant current drive can be used as a constant current output of switch type converter. In addition, the province electricity or high efficiency switching power demand is the indispensable element in the LED lighting application, and the hysteresis type pulse frequency modulation technology ( 滞后烤瓷) Can a sharp rise in the light load or overloading of the power conversion efficiency. This article explores how to use the constant current LED driver design high efficiency, high stability of the LED lighting system.

the traditional LED driver: constant voltage mode LED

the current determines the brightness of LED, the greater the current, the brightness of the leds will be brighter. In general, the use of constant voltage or constant current drive can achieve the goal of light LED. Figure 1 is the most simple constant voltage LED driver, flowing through the LED current is controlled by and LED series resistance. For example, assume that the input voltage is 5 v, the LED forward bias is 3. 6 v, under the condition of the, if you need the LED current to 20 ma, need to use the resistor of 70 Ω. Although the architecture of this method is very simple, but the current of the LED will change with the voltage at the ends of the fall in LED, LED forward bias if inconsistency or there is some change in the input voltage will affect the brightness of the LED. In addition, in the power loss on the resistor can cause overheating and the low efficiency problem.

the traditional LED driver: constant current mode

another common LED drive as shown in figure 2, the mode of constant current drive. In figure 2, the current of the LED by the linear voltage regulator, the current can be made of R1 resistance setting. Compared with the constant voltage mode driver, constant current mode LED driver can control the current without being LED forward bias and is influenced by the different input voltage. But if the input voltage and the LED forward always bias between the differential pressure is too large, will cause overheating problem on the drive.

hysteresis type pulse frequency modulation

MBI6650 hysteresis model of pulse frequency modulation control method can effectively improve the system efficiency under light load application. Figure 3 for the application of MBI6650 circuit, figure 4 is hysteresis model pulse frequency modulation way of wave type diagram. In figure 3 VSEN RSEN resistance at the ends of the pressure drop, MBI6650 output current is by the voltage and resistance. In figure 4 VH for MBI6650 internal reference voltage of high and its value is 1 VSEN voltage. Three times, and VL VSEN 0. Seven times. MBI6650 working principle is: when the power is opened, VSEN below the VH, therefore MBI6650 built-in MOSFET and the inductance current is added at the ends of the joint across in RSEN VSEN increases. When VSEN equals the VH, built-in MOSFET will be closed, the inductor current through the diode ( D1) Discharge decreases, and thus make VSEN voltage drops. When voltage is equal to the VL VSEN, built-in MOSFET will open again and again repeat before action. Due to the nature of hysteresis type pulse frequency modulation, the inductance current remains in continuous conduction mode ( CCM) , which is of great help to reduce the LED ripple current.

this kind of control method of switching frequency will change with load current, the greater the current frequency is lower. Under the same load conditions, the bigger the inductance its switching frequency will be lower. Switching frequency controlled in more than 40 KHZ MBI6650 in order to avoid the happening of audio noise.

besides can improve the light load efficiency, hysteresis type pulse frequency modulation control method also has other advantages, for example, due to the use of high pressure measuring current limiting technology, and the loss of power consumption on a current limiting resistor is very small, so can use smaller volume of current limiting resistor, the circuit board to save space and cost of components is helpful.

figure 3: MBI6650 application circuit.

figure 4: hysteresis type pulse frequency modulation control method of wave type diagram.

protection function to ensure that the LED lighting system and the safety and reliability of the drive, MBI6650 provide several kinds of protection function at the same time. For example, low voltage protection, UVLO) To avoid wrong IC due to insufficient input voltage operation, it provides the hysteresis voltage can avoid the noise when the phone is switched on. Open circuit and short circuit protection to protect the drive due to affected by the fault of damage. MBI6650 also provide over temperature protection, when arrived at 140 ° C, the IC chip IC will shut down automatically output current to avoid overheating on IC produce damage, and when the temperature dropped to 95 ° C, the IC will work again only.

summary of this article is to design a safe and effective LED lighting system, the accumulation of science and technology launched MBI6650 has considerable advantages, for example: with hysteresis type pulse frequency modulation technologies to promote the efficiency of the light load when, can improve the service life of the LED constant current control, and provide several kinds of protection function to ensure the safety and reliability of lighting system. Compared with the traditional LED drive, MBI6650 precise output current and high conversion efficiency is more suitable for the application of LED lighting system.

the author: Wu Zhiyu application engineering, accumulated technology co. , LTD