MP1048 – FULL BRIDGE CCFL CONTROLLER
Careful management of limit conditions
provides graceful reduction of lamp power at
low supply voltages but allows the loop to
recover quickly from an abrupt step in supply
voltage. System fault management facilities
include an on-chip open-lamp regulator, a
transformer secondary peak current regulator
and a dual-mode fault timer.
Higher phase delay will lead to higher primary
RMS current and therefore higher transformer
temperature. With ZCS, A & D conduction starts
at the zero crossing of IPRI.
The MP1048 does not utilize ZVS or ZCS. It
implements fast switching to reduce switching
loss and operates at the condition that IPRI and
VPRI are in phase to reduce primary RMS
current. Therefore, higher efficiency than ZVS
or ZCS is achieved.
By regulating the peak current in the
transformer secondary winding, UL1950 can be
met for most systems. When the MP1048 is
regulating open lamp voltage, it ignores the
burst control and runs continuously to ensure
either the lamp has a chance to re-ignite or the
fault timer can smoothly and accurately time
out. If the MP1048 detects an open lamp
condition for a time that exceeds the timer
interval, it will shutdown until the part is turned
off and then turned on again. Similarly, the
MP1048 will shutdown if it detects an
over-current condition in the secondary for
about 2% of the open lamp timer interval. If
required, the secondary over-current timeout
can be shortened with external components.
On-chip current limit protects the MP1048 in
case of output fault conditions.
V
V
PS
PS
A
B
C
D
D1
V
PRI
-
+
I
PRI
A,D
B,C
V
I
:
:
PRI
PRI
ZVS
ZCS
0
0
0
FEATURE DESCRIPTION
All reference designators refer to the MP1048
Block Diagram, unless otherwise designated.
MP1048
Figure 2—VPRI vs. IPRI
Brightness Control
The MP1048 can operate in four modes:
Analog Mode, Burst Mode with a DC input,
Burst Mode with an external PWM or Analog
and Burst Mode. The four modes are
dependent on the pin connections defined
under Pin Functions.
High Efficiency Operation
There are two major power losses in a CCFL
inverter: switching loss of switches and copper
loss of the transformer winding. To reduce
switching loss, Zero Current Switching (ZCS as
described in US patent 6,114,814) or Zero Voltage
Switching (ZVS) are commonly implemented.
As shown in Figure 2, ZCS and ZVS require
Choosing the required burst repetition
frequency can be achieved by an RC
combination as defined in component selection.
The MP1048 has a soft-on and soft-off feature
to reduce noise when using burst mode
dimming. Analog dimming and Burst dimming
are independent of each other and may be
used together to obtain a wider dimming range.
primary current IPRI lagging primary voltage VPRI
.
With ZVS, since D1 can only conduct at the
negative phase of IPRI, the beginning of A & D
conduction will only happen at the negative
phase of IPRI.
MP1048 Rev. 0.9
9/24/2007
www.MonolithicPower.com
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2007 MPS. All Rights Reserved.
7
MPS [ MONOLITHIC POWER SYSTEMS ]
