鈥?/div>
Open Lamp Detection Circuitry
DESCRIPTION
The UC3872 is a resonant lamp ballast controller optimized for driving
cold cathode fluorescent, neon, and other gas discharge lamps. The res-
onant power stage develops a sinusoidal lamp drive voltage, and mini-
mizes switching loss and EMI generation. Lamp intensity adjustment is
accomplished with a buck regulator, which is synchronized to the external
power stage鈥檚 resonant frequency. Suitable for automotive and battery
powered applications, the UC3872 draws only 1碌A(chǔ) when disabled.
Soft start and open lamp detect circuitry have been incorporated to mini-
mize component stresses. Open lamp detection is enabled at the comple-
tion of a soft start cycle. The chip is optimized for smooth duty cycle
control to 100%.
Other features include a precision 1.2% reference, undervoltage lockout,
and accurate minimum and maximum frequency control.
BLOCK DIAGRAM
3
VC
VCC 10
REF
9
(HIGH=ENABLE)
UVLO
3.0V
REF
50k
PUSH PULL
OUTPUTS
N-CHANNEL
2
AOUT
ENBL 11
0.1V
COMP
INV
4
6
20碌A(chǔ)
1.5V
SS
5
200碌A(chǔ)
0.2V
+
CT
7
OSCILLATOR
ZERO DETECT
ZD
8
0.5V
SENSE
OUT
SYNC
+
鈥?/div>
TOGGLE
T
PWM
鈥?/div>
EA
+
OPEN
LAMP
DETECT
1
50k
BOUT
鈥?/div>
鈥?/div>
1
+
R
S
50k
12 COUT
BUCK DRIVE
P-CHANNEL
13 PGND
14
GND
鈥?/div>
+
Note: Pin numbers shown are for DIP package.
UDG-99112
07/99
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