MP1039 – 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.
By regulating the peak current in the
transformer secondary winding, UL60950 can
be met for most systems. When the MP1039 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 MP1039 detects an open lamp
condition for a time that exceeds the timer
interval, it will shut down until the part is turned
off and then turned on again. Similarly, the
MP1039 will shut down 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.
The MP1039 does not utilize ZVS or ZCS. It
implements fast switching to reduce switching
loss and operates at the condition that I
PRI
and
V
PRI
are in phase to reduce primary RMS
current. Therefore, higher efficiency than ZVS
or ZCS is achieved.
V
PS
A
V
PS
C
D1
+
V
PRI
I
PRI
-
B
D
A,D
V
PRI
:
ZVS
I
PRI
:
ZCS
B,C
0
0
0
MP1039
FEATURE DESCRIPTION
All reference designators refer to Figure 1,
unless otherwise designated.
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
primary current I
PRI
lagging primary voltage V
PRI
.
With ZVS, since D1 can only conduct at the
negative phase of I
PRI
, the beginning of A & D
conduction will only happen at the negative
phase of I
PRI
.
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 I
PRI
.
Figure 2—V
PRI
vs. I
PRI
Brightness Control
The MP1039 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.
Choosing the required burst repetition
frequency can be achieved by an RC
combination, as defined in component
selection. The MP1039 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.
MP1039 Rev. 1.1
9/24/2007
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7
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