LT3420/LT3420-1
Photoflash Capacitor
Chargers with Automatic Refresh
DESCRIPTIO
The LT
®
3420/LT3420-1 charge high voltage photoflash
capacitors quickly and efficiently. Designed for use in both
digital and film cameras, these devices use a flyback
topology to achieve efficiencies up to four times better
than competing flash modules. A unique adaptive off-time
control algorithm* maintains current-limited continuous
mode transformer operation throughout the entire charge
cycle, eliminating the high inrush current often found in
modules.
The LT3420/LT3420-1 output voltage sensing scheme*
monitors the flyback voltage to indirectly regulate the
output voltage, eliminating an output resistor divider or
discrete zener diode. This feature allows the capacitor to
be held at a fully charged state without excessive power
consumption. Automatic refresh (which can be defeated)
allows the capacitor to remain charged while consuming
an average input current of about 2mA, at a user-defined
refresh rate. A logic high on the CHARGE pin initiates
charging, while the DONE pin signals that the capacitor is
fully charged.
, LTC and LT are registered trademarks of Linear Technology Corporation.
*U.S. Patent #6,518,733
FEATURES
s
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Charges 220µF to 320V in 3.7 Seconds
from 5V (LT3420)
Charges 100µF to 320V in 3.5 Seconds
from 5V (LT3420-1)
Charges Any Size Photoflash Capacitor
Supports Operation from Two AA Cells or Any
Supply from 1.8V to 16V
Controlled Peak Switch Current: 1.4A (LT3420)
1.0A (LT3420-1)
Controlled Input Current: 840mA (LT3420)
450mA (LT3420-1)
Uses Standard Transformers
Efficient Flyback Operation (>75% Typical)
Adjustable Output
Automatic Refresh
Charge Complete Indicator
No High Voltage Zener Diode Required
No Output Voltage Divider Required
Small 10-Lead MSOP Package
APPLICATIO S
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s
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Digital Camera Flash Unit
Film Camera Flash Unit
High Voltage Power Supplies
TYPICAL APPLICATIO
V
BAT
1.8V TO 6V
C1
4.7µF
5,6
3,4
DANGER HIGH VOLTAGE
OPERATION BY HIGH VOLTAGE
TRAINED PERSONEL ONLY
V
CC
2.5V TO 10V
4
C2
4.7µF
9
8
51.1k
2
V
BAT
V
CC
LT3420
CHARGE
DONE
C
T
10
0.1µF
R
REF
GND
5
3
R
FB
6
SW
SEC
T1
1:12
8
D1
320V
V
BAT
1.8V TO 6V
C1
4.7µF
1
DANGER HIGH VOLTAGE
OPERATION BY HIGH VOLTAGE
TRAINED PERSONEL ONLY
C3
220µF
7
330V
PHOTOFLASH
CAPACITOR
1
+
V
CC
2.5V TO 6V
CHARGE
DONE
CHARGE
DONE
C2
4.7µF
9
8
2k
C1, C2: 4.7µF, X5R or X7R, 10V
C3: RUBYCON 220µF PHOTOFLASH CAPACITOR
T1: TDK SRW10EPC-U01H003 FLYBACK TRANSFORMER
D1: GENERAL SEMICONDUCTOR GSD2004S SOT-23
DUAL DIODE. DIODES CONNECTED IN SERIES
3420 F01
C1, C2: 4.7µF, X5R or X7R, 6.3V
C3: RUBYCON 100µF PHOTOFLASH CAPACITOR
T1: KIJIMA MUSEN SBL-5.6S-2
D1: GENERAL SEMICONDUCTOR GSD2004S SOT-23
DUAL DIODE. DIODES CONNECTED IN SERIES
Figure 1. High Charge Rate LT3420 Photoflash Circuit
Figure 2. Small Size LT3420-1 Photoflash Circuit
3420fa
U
4
U
U
T1
1:10
4
5
D1
320V
3
60.4k
2
V
BAT
V
CC
LT3420-1
CHARGE
DONE
C
T
10
0.1µF
R
REF
GND
5
1
3
R
FB
6
SW
SEC
6
7
C3
100µF
330V
PHOTOFLASH
CAPACITOR
+
2k
3420 F02
1
LINER [ LINEAR TECHNOLOGY ]
