QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC690 STROBE CAPACITOR CHARGER, HIGH VOLTAGE SUPPLY LT3420EMS-1 DESCRIPTION Demonstration circuit 690 is a DC-DC flyback converter eras and high voltage supplies that require high effi- using the LT3420EMS1 to rapidly charge an output ca- ciency and small size. pacitor to 300V for photoflash applications. It demon- strates a simple application circuit operating in high effi- Design files for this circuit board are available. Call ciency and shows appropriate layout techniques for the the LTC factory. LT3420EMS 1. The circuit uses small surface mount components and has very small board space compared LT is a trademark of Linear Technology Corporation to conventional solutions. This demonstration circuit is particularly useful for applications such as digital cam- QUICK START PROCEDURE Demonstration circuit 690 is easy to set up to evaluate 5. Slowly turn on power source Vbatt and Vcc. Check for the performance of the LT3420EMS1. Refer to Figure 1 the proper output voltages. Vout= 320V. for proper measurement equipment setup and follow the NOTE: If there is no output, temporarily disconnect the procedure below: load and input power source, and make sure that JP2 NOTE: When measuring the input or output voltage rip- is set to ON position. ple, care must be taken to avoid a long ground lead on 6. Measure the charge time (Vout rise time from 0V to the oscilloscope probe. Measure the input or output 320V) from scope, it should be about 3 seconds. The voltage ripple by touching the probe tip directly across photoflash capacitor should be pre-charged a few the Vin or Vout and GND terminals. See Figure 2 for times before the measurement test due to its memory proper scope probe technique. characteristic. NOTE: For safe operation, always shield the circuit when 7. For efficiency measurement, connect a high voltage power is on, and always discharge the high voltage out- adjustable load box between the +Strobe Cap and put capacitor after power is off. Strobe Cap terminals, adjust load and set the Vout = 1. With power off, connect input power source Vbatt to 300V. Measure the Vin, Iin, Vout and Iout and calcu- the Vbatt and GND terminals. Input voltage is limited late the efficiency. For Vin=3.3V, the efficiency should to between 1.8V to 6V. be above 70%. 2. Set JP1 to DISCONNECT position for separate input 8. For single source operation, set the input source se- power operation. Connect input power source Vcc to lector Jumper JP1 to CONNECT position. Remove the the Vcc and GND terminals, and limit the input voltage connection of power source Vcc. Limit the input volt- from 2.3V to 6V. age from 2.3V to 6V. Vcc will be powered from Vbatt. 3. Connect load (a 70uF, 330V photoflash capacitor) be- 9. To shut down the circuit, connect the JP2 to OFF posi- tween the +Strobe Cap and Strobe Cap terminals. tion. The output capacitor charging is disabled. 4. Set JP2 to ON position to enable Charge operation. Warning: Operate by high voltage trained personnel only. 1 GND VIN QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC690 STROBE CAPACITOR CHARGER, HIGH VOLTAGE SUPPLY Figure 1. Proper Measurement Equipment Setup Figure 2. Measuring Input or Output Ripple Figure 3. Charge time for charging 70uF, 330V photoflash capacitor. CH4: Vout, 100V/Div. Vin=3.3V, Vout=300V. 2