AN880 APPLICATION NOTE THE L6569: A NEW HIGH VOLTAGE IC DRIVER FOR ELECTRONIC LAMP BALLAST by G. Calabrese and T. Castagnet Figure 1: CFL series resonant half bridge inverter. INTRODUCTION Electronic lamp ballasts are now popular in both consumer and industrial lighting. They offer power saving, flicker free operation and reduced sizes. Improvements to the light control and cost reduc- tion of the ballast will broaden their market accep- tance. Today designers focus on reducing the cost of the ballast, but also work to add features to the bal- last like saving energy by dimming the light, or in- creasing the life time with better preheat and pro- tections. Such requirements have contributed to the development of dedicated high voltage con- trollers like the L6569, which are able to drive the floating transistor of a symmetric half bridge in- verter. This device is a simple, monolithic oscilla- tor-half bridge driver that allows quick design of the ballast. Figure 2: Current and voltage of the STD3NA50 MOSFETs when driven in ZVS with the L6569. HIGH VOLTAGE IC DRIVERS IN BALLAST AP- PLICATIONS ID The voltage fed half bridge VDS Voltage fed series resonant half bridge inverters are currently used for Compact Fluorescent Lamp GND ballasts (CFL), for Halogen Lamp transformers, and for many European Tube Lamp (TL) ballasts. This simple converter is preferred for new de- LVG GND signs, because it minimizes the off state voltage of the power transistors to the peak line voltage, RF GND and requires only one resonant choke. In addition this choke protects the half bridge against short 2 s/dv 50 V/dv 0.1 A/dv circuits across lamp terminals. However overheat- ing and overcurrent occur during open load op- eration. The inverter robustness must be im- gle frequency with a saturable pulse transformer proved, or some protections are required. (see fig. 1) to drive the transistors. This type of The half bridge inverter operates in Zero Voltage design has a higher component count, a higher Switching (ZVS) resonant mode 1 , to reduce the tolerance on the switching frequency, and it can- transistor switching losses and the electromag- not adjust the lamp power. netic interference generated by the output wiring The only way to design a cost effective, compact and the lamp. and smart control of the lamp is to use a dedi- cated I.C. that is able to drive the upper transistor of an symmetric half bridge inverter. Such control- lers require a high voltage capability for the float- Fully integrated ballast controllers ing transistor driver 2 . MOSFETs are preferred By varying the switching frequency, the half over Bipolar transistors as power switches be- bridge inverter is able to modulate the lamp cause their gate driver requires a lower supply power. However most current designs use a sin- current and a smaller silicon size 3 . February 2003 1/14AN880 APPLICATION NOTE and the circuit requires only 150 A at power up. THE L6569 AND ITS APPLICATIONS The L6569 integrates a high voltage Lateral The L6569 DMOS transistor in place of the usual external di- The L6569 is able to directly control a symmetric ode 2 to charge the bootstrap capacitor for the half bridge inverter of a fluorescent lamp ballast, upper buffer. Figure 5 shows DMOS operating as or a low voltage halogen lamp transformer.Two a synchronous rectifier. 270mA buffers drive the inverter MOSFETs in complementary fashion with a 1.25s built-in dead time to prevent cross conduction. The buffer The applications for the upper Mosfet is driven through a 600V The primary application for the L6569 is the Com- level shifter realized in BCD off line technology. pact Fluorescent Lamp. With the oscillator, the The oscillator, similar to a CMOS 555 timer, oper- supply and the Mosfet drivers it is the core of the ates from 25 to 150 kHz with a +/-5% maximum application, and designers can customize the cir- tolerance. The internal 15V shunt regulator has a cuit to their requirements. 9V Under Voltage Lock Out with an 1V hysteresis, Figure 3: Block diagram of the L6569. VS BOOT CHARGE UVLO PUMP LEVEL HVG SHIFTER HIGH SIDE RF DRIVER OUT CF LOGIC CONTROL with DEAD TIME LVG LOW SIDE DRIVER GND Figure 4: Basic application diagram using the L6569 and two STD4NK50Z MOSFETs. 100nF 180KW 22W 10m F STD4NK50Z L6569 10KW LAMP 10m F AC LINE 22W 1nF D02IN1385 2/14