Page 23

EETE NOVEMBER 2012

Fig. 3: LED Efficiency in the circuit diagram of figure 2. set from 0V to 60V enabling to drive a wide range of LEDs in a single string. A typical 50W headlight application is shown in figure 2. This application uses a single inductor to accurately regulate a 25V string of LEDs at 2A to deliver 50W of LED power. This circuit offers a 50:1 PWM dimming ratio which is ideal for anti-glare auto-dimming requirements. Both input and output (LED) cur- rent is monitored while fault protection is provided to survive and report and open or shorted LED condition. Its internal 4 switch buck-boost controller operates from input voltages above, below or equal to the output voltage mak- ing it ideal for applications, such as automotive, where the input voltage can vary dramatically during stop/start, cold crank and load dump scenarios. Transitions between buck, pass-through and boost operating modes are seamless, offering a well regulated output in spite of wide variations of supply voltage. The LT3791’s unique design utilizes three control loops monitor input current, LED current and output voltage to deliver optimal performance and reliability. It uses four external switching MOSFETs and can deliver from 5W to over 100W of continuous LED power with efficien- cies up to 98% as can be seen in figure 3. In conventionally powered vehicles high efficiency is important as it minimizes the Visit us: need for heat sinking enabling a very compact low profile foot- Hall B3, Booth 559 print. However, in EVs this power savings adds valuable miles of vehicle range between charges. > circuit protection LED current accuracy of +6% ensures constant lighting connectors in an LED string while + 2% output voltage accuracy offers emc products several LED protection features and also enables the converter switches to operate as a constant voltage source. The LT3791 can use input systems either analog or PWM dimming as required by the applica- ems tion. Furthermore, its switching frequency can be programmed schurter.com between 200 and 700kHz or synchronized to an external clock. Additional features include output disconnect, input and output current monitors, and integrated fault protection. www.electronics-eetimes.com Electronic Engineering Times Europe November 2012 23


EETE NOVEMBER 2012
To see the actual publication please follow the link above