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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

using the LT3420EMS–1 to rapidly charge an output ca-

pacitor to 300V for photoflash applications. It demon-

strates a simple application circuit operating in high effi-

ciency and shows appropriate layout techniques for the

LT3420EMS– 1. The circuit uses small surface mount

components and has very small board space compared

to conventional solutions. This demonstration circuit is

particularly useful for applications such as digital cam-

eras and high voltage supplies that require high effi-

ciency and small size.

Design files for this circuit board are available. Call

the LTC factory.

LT is a trademark of Linear Technology Corporation

QUICK START PROCEDURE

Demonstration circuit 690 is easy to set up to evaluate

the performance of the LT3420EMS–1. Refer to Figure 1

for proper measurement equipment setup and follow the

procedure below:

NOTE:

When measuring the input or output voltage rip-

ple, care must be taken to avoid a long ground lead on

the oscilloscope probe. Measure the input or output

voltage ripple by touching the probe tip directly across

the Vin or Vout and GND terminals. See Figure 2 for

proper scope probe technique.

NOTE:

For safe operation, always shield the circuit when

power is on, and always discharge the high voltage out-

put capacitor after power is off.

With power off, connect input power source Vbatt to

the Vbatt and GND terminals. Input voltage is limited

to between 1.8V to 6V.

Set JP1 to DISCONNECT position for separate input

power operation. Connect input power source Vcc to

the Vcc and GND terminals, and limit the input voltage

from 2.3V to 6V.

Connect load (a 70uF, 330V photoflash capacitor) be-

tween the +Strobe Cap and –Strobe Cap terminals.

Set JP2 to ON position to enable Charge operation.

Slowly turn on power source Vbatt and Vcc. Check for

the proper output voltages. Vout= 320V.

NOTE:

If there is no output, temporarily disconnect the

load and input power source, and make sure that JP2

is set to ON position.

Measure the charge time (Vout rise time from 0V to

320V) from scope, it should be about 3 seconds. The

photoflash capacitor should be pre-charged a few

times before the measurement test due to its memory

characteristic.

For efficiency measurement, connect a high voltage

adjustable load box between the +Strobe Cap and –

Strobe Cap terminals, adjust load and set the Vout =

300V. Measure the Vin, Iin, Vout and Iout and calcu-

late the efficiency. For Vin=3.3V, the efficiency should

be above 70%.

For single source operation, set the input source se-

lector Jumper JP1 to CONNECT position. Remove the

connection of power source Vcc. Limit the input volt-

age from 2.3V to 6V. Vcc will be powered from Vbatt.

To shut down the circuit, connect the JP2 to OFF posi-

tion. The output capacitor charging is disabled.

Warning: Operate by high voltage trained personnel only.