DC515A Analog Devices

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 515 CCFL POWER SUPPLY LT1373 DESCRIPTION Demonstration Circuit 515 is a single output CCFL DC515 is designed to operate for a V range of 5V IN inverter with dimming and over-voltage protection 20V and outputs hundreds of volts at mA current lev- features. The inverter consists of a LT1373 and a els. Royer converter that uses bipolar transistors. The Dimming can be achieved by either an analog signal featured LT1373 limits its switch current to 1.5A, or a PWM signal applied to the Vprog terminal, or by which protects against CCFL short circuit conditions. adjusting a potentiometer. The over-voltage protec- The Royer topology is very flexible in that it operates tion feature (when enabled) protects the Royer trans- over wide supply ranges, and it scales well over a former from excessive high voltages when the CCFL broad output power range while keeping component is not connected to the output. count low. DC515 is most suitable for 2W6W CCFL Design files for this circuit board are available. applications such as point-of-sale terminals and Call the LTC factory. automotive LCD displays. QUICK START PROCEDURE DC515 is easy to set up to evaluate the performance NOTE: 5V8V input may be too low a voltage for of the LT1373. Refer to Figure 1 for proper meas- some LCDs CCFLs that have unusual characteris- urement equipment setup and follow the procedure tics. If one such LCD is being used contact the below: LTC Applications Department for directions on how the board can be modified to operate down to 5V. 1. Connect the LCD CCFL across the CCFL and + terminals E5 and E6. Connect the positive CCFL 4. Carefully adjust R2 until the CCFL current equals wire to E5 and the negative terminal of the CCFL the maximum current for which the CCFL is speci- to E6. fied. Warning: There may be thousands of volts across 5. Apply the system V supply to the Vprog ter- PROG the CCFL and + terminals, across the capacitor minal. Set the V voltage to its specified PROG C1, and on the secondary side of the transformer maximum (5V is the limit). Adjust R8 until zero cur- T1. These high voltages can be very harmful to rent flows in the CCFL. CCFL current can now be anyone who touches these points. adjusted over its full range by adjusting V PROG over its full range. 2. Ground the LCD Casing. 3. Apply 8V20V to the Vin and Gnd terminals. 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 515 CCFL POWER SUPPLY + + + TRUE RMS + CURRENT METER* CURRENT PROBE CCFL LCD LCD CASE CCFL CONNECTOR * FOR A DESCRIPTION OF HOW TO ACCURATELY MEASURE CCFL CURRENT, SEE LINEAR TECHNOLOGY APPLICATION NOTE 65 (AN65), APPENDIX C Figure 1. Proper Measurement Equipment Setup 2 + +