Dell 2000FP Service Manual page 30

Dell 2000FP LCD Monitor Service Guide
VREF
IC701
TL1451
The TL1451AC incorporates on a single monolithic chip all the functions required in the construction of two
pulse-width modulation control circuits. Designed primarily for power supply control, the TL1451AC contains
an on-chip 2.5V regulator two error amplifiers, an adjustable oscillator, two dead-time comparators,
undervoltage lockout circuitry, and dual common-emitter output transistor circuits. The uncommitted output
transistors provide common-emitter output capability for each controller. The internal amplifiers exhibit a
common-mode voltage range from 1.04V to 1.45V. The dead-time control comparator has no offset unless
externally altered and can provide 0% to 100% dead time. The on-chip oscillator can be operated by erminating
RT and CT. During low Vcc conditions, the undervoltage lockout control circuit feature locks the outputs off
until the internal circuitry is operational.
Feed-back Circuit
C707
R707
10K
0.01U
C703
C705
1U
16V (OPEN)
(1206)
(SHORT)
C702 R705 C704
680P 10K (OPEN)
(1%)
R706
10K
R708
10K
R718
1.8K
(1%)
R719
1.1K
(1%)
Confidential
R711
5.1K
R710 R712
5.1K 47K
C706
0.01U
Fig. 2
C717
1200P
50V
R726
330
1/4W
(1206)
Fig. 3
5
Circuit Operation Theory
VREF
C709
R723
1U
OPEN
16V
(1206)
R713
47K
C708
1U
16V
(1206)
VREF
R724 C710
OPEN 1U
16V
(1206)