QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 515
CCFL POWER SUPPLY
LT1373
DESCRIPTION
Demonstration Circuit 515 is a single output CCFL
inverter with dimming and over-voltage protection
features. The inverter consists of a LT1373 and a
Royer converter that uses bipolar transistors. The
featured LT1373 limits its switch current to 1.5A,
which protects against CCFL short circuit conditions.
The Royer topology is very flexible in that it operates
over wide supply ranges, and it scales well over a
broad output power range while keeping component
count low. DC515 is most suitable for 2W–6W CCFL
applications such as point-of-sale terminals and
automotive LCD displays.
DC515 is designed to operate for a V
IN
range of 5V–
20V and outputs hundreds of volts at mA current lev-
els.
Dimming can be achieved by either an analog signal
or a PWM signal applied to the Vprog terminal, or by
adjusting a potentiometer. The over-voltage protec-
tion feature (when enabled) protects the Royer trans-
former from excessive high voltages when the CCFL
is not connected to the output.
Design files for this circuit board are available.
Call the LTC factory.
QUICK START PROCEDURE
DC515 is easy to set up to evaluate the performance
of the LT1373. Refer to Figure 1 for proper meas-
urement equipment setup and follow the procedure
below:
1.
Connect the LCD\CCFL across the CCFL – and +
NOTE:
5V–8V input may be too low a voltage for
some LCDs\CCFLs that have unusual characteris-
tics. If one such LCD is being used contact the
LTC Applications Department for directions on how
the board can be modified to operate down to 5V.
terminals E5 and E6. Connect the positive CCFL
wire to E5 and the negative terminal of the CCFL
to E6.
Warning:
There may be
thousands of volts
across
the CCFL – and + terminals, across the capacitor
C1, and on the secondary side of the transformer
T1.
These high voltages can be very harmful to
anyone who touches these points.
2.
Ground the LCD Casing.
3.
Apply 8V–20V to the Vin and Gnd terminals.
4.
Carefully adjust R2 until the CCFL current equals
the maximum current for which the CCFL is speci-
fied.
5.
Apply the system V
PROG
supply to the Vprog ter-
minal. Set the V
PROG
voltage to its specified
maximum (5V is the limit). Adjust R8 until zero cur-
rent flows in the CCFL. CCFL current can now be
adjusted over its full range by adjusting V
PROG
over its full range.
1
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