Research On Integrated Circuit Of Off-chip Capacitor Free Hysteresis Current Control Large Current LED Driver

In recent years,with the development of high-brightness LED technology,high-brightness LED lighting solutions have gradually replaced traditional lighting such as fluorescent lighting and incandescent lamps for its advantages in longer lifetime and better luminous efficiency and it is widely used in outdoor lighting,automotive lighting,industrial lighting and other areas that require high product reliability and efficiency.Since different places have different lighting environment and different requirement,or say,different input voltage,numbers of LEDs,the job of a LED driver is to ensure the LEDs working properly under different condition and offer dimming control.The essence of the structure of LED is a P-N junction,so they have the same V-I characteristic,and the brightness of a LED is relate to its forward current.So driving LED is to regulate the current through it,which is different from traditional voltage source.For high-brightness LED,the forward current of it is usually large and the set-up time of the output current is long which may affect the performance of PWM dimming,limit its application range.In order to meet as much as possible situations,LED driver needs appropriate current regulating metho and cut the use of off-chip components which will bring extra cost.Under this background,a high-current LED driver without off-chip power MOSFET bootstrap capacitors and output filter capacitors is designed in this paper,which can driving different numbers of LEDs properly under different input voltage without extra off-chip components.The proposed high-side power transistor gate driver gets rid of the reliance on off-chip capacitors in traditional high-side power transisitor gate driver.Moreover,the set-up time of the output current is short enough to have wide range of PWM dimming to meet different brightness requirement,and the problem of the variation of switching frequency in traditional hysteresis current control under different numbers of output LEDs is alleviated by the using of pseudo-constant frequency current control,which simplifies the EMI design.This paper first briefly explains the basic principles of large-current LED driving,and then the circuit design,the simulation results as well as their performance of every module is presented.Lastly,part of the layout design and the comparison between the pre-simulation and post-simulation is given.The proposed LED driver is implemented in BCD 30V process of DB Hitek of Korean with the dimming range of 10%—100%,the input voltage range is 6—30 V and maximum output LED amounts is 9.The presented LED driver can regulating a stable average output current(700 mA)under different input voltage and different numbers of output series LEDs,the relatively change rate is 4.40%and the maximum output current ripple is 167.61 mA.Moreover,with a certain input voltage,the presented LED driver can stabilize the switching frequency under different load,the largest switching period change is 351.7 ns,which is 78.98%better than the traditional hyteresis current control and its peak efficiency is up to 93.1%.Above all,the presented LED driver satisfies the basic requirement of large-current LED driving as well as reduces the application cost,which meets the expected functions.