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the duration of the square wave by 500 ns (this value is set by
R3640 and C2640).
A demagnetisation winding (pin 1-2 of L5600) detects when
there is no energy in the transformer. This information is fed to
IC7650 pin 7 and this is used to switch 'on' the MOSFET
(7610). In this way, the dissipation is very low, combined with a
low EMI.
The MOSFET 7610 is switched 'off' at high currents, up to 15
A. To reduce dissipation, this is done at high speed for which
'turn off driver' T7608 is used.
The output voltage (400 V) is divided by R3670 and R3671 and
connected to pin 3 of IC7650. A change in the load will adjust
the duty cycle of the gate pulse at pin 11, in order to keep the
output voltage constant. Therefore, there is no need to adjust
the output voltage by means of a potentiometer.
Protections
Current Protection
The current through FET 7610 flows also through the sense
resistors 3614 and 3615. The voltage across these resistors is
fed to pin 6 of IC7650. If the current exceeds its reference level,
the pre-conditioner will switch 'off'. A filter, formed by C2666
and R3666, avoids unnecessary protection triggering due to
spikes.
C2665 and R3665 on pin 13 determine the maximum
oscillating frequency.
9.2.6
LLC Supply (Diagram P6)
Introduction
The V
supply (70-90V) is based upon the so-called LLC
S
converter technology (also used in the MG3.1 and FTV1.9). It
is used to supply the power of the sustain pulses, which
generate the light in the PDP. The voltage is set by a reference
DC voltage (V
), coming from the PDP.
RS
The V
voltage (derived from V
A
for driving the addressing electrodes of the PDP. The value of
V
is also depending on a reference voltage (V
A
the PDP.
The main supply hosts the following supplies:
•
V
supply, via a LLC converter.
S
•
V
supply, via the LLC supply and a down converter.
A
•
V
, via a flyback converter.
CC
•
3V3, via a down converter.
•
Audio amplifier supplies (V
transformer.
6007
DRIVER
5001
6008
7001
14
12
FAULT INPUT
FASE
10
CONTROL-IC
MC34067
Figure 9-4 V
The start-up voltage for the control IC 7001 is derived from one
phase, the IC starts to oscillate, and alternately S1 (7005) and
S2 (7006) are driven into conduction with a dead time in
between. This effects that, via the resonance circuit and the
Circuit Descriptions and List of Abbreviations
) is used to supply the power
S
) coming from
RA
and V
), via a
SND_POS
SND_NEG
+400V-HOT
POWER
BLOCK
S1
7005
3014
5002
6044
S2
7006
3017
FEEDBACK
7002
VCC
VAUX
SENSING
7010
CL 16532099_109.eps
Supply
S
MOSFETS, energy is stored into transformers L5002/5004 and
capacitor C2001. Compared with the FM23, two transformers
are used, to be able to deliver the higher power for the 42" PDP.
The secondary voltages are rectified and smoothed. These
voltages are, via a voltage divider, fed to the optocoupler that
influences the oscillator frequency of the control IC and
stabilises the secondary voltages. If the current becomes too
high, the supply is switched 'off' via the fault input of the control
IC.
Advantages:
•
High efficiency (more then 90%, other supplies 75%).
•
Less radiation.
•
More cost-effective (two MOSFETS of 400 V are cheaper
than one MOSFET of 600 V).
Disadvantages:
•
Very low power stand-by impossible.
•
Realisation and stabilisation is more complex.
Operation V
Figure 9-5 Impedance Characteristic
General
The LLC supply is a serial resonance power supply. The coil,
resistor, and capacitor form a trap at the resonance frequency
f
. The impedance is frequency dependent. The smallest
R
impedance is at the resonance frequency (f
of f
is the inductive part, and at the left side the capacitive part.
R
The supply works in the inductive part, since higher
frequencies causes minor losses.
Stabilisation is realised, by regulating the frequency as function
of the output voltage (V
stabilised by influencing the series-loop. The higher the
frequency, the lower the output power.
The supply voltage of the control IC comes from the 25V_HOT
voltage of the standby supply (via stabiliser 7093), and is lead
to pin 15 of the IC. The IC starts to oscillate. This supply line
has a short-circuit protection via opto-coupler 7003; when the
STBY supply is regulating, the current through the opto-coupler
is amplified and will deliver power to the IC.
Vs
Control is done in the usual way by a TL431 at the secondary
+
side. V
RS
additional TL431 (7011 at schematic P6). V
coming from the display, influences the output of the V
The output voltage of the V
following formula: V
circuitry for V
is possible to adjust the voltage, via potmeter R3026). The V
is fed via a voltage divider to IC7010 (TL431).
If the voltage at pin 3 of IC7010 is higher than 2.5 V, a current
will flow from cathode to anode. This current flows also through
260901
the secondary side of the optocoupler 7002.
The voltage at pin 7 of the MC34067, determines the output
frequency. The higher this voltage, the higher the output
frequency. Thus, if the voltage on pin 7 increases, the
frequency increases and V
So, when the output voltage rises, the voltage at the reference
IC7010 also rises, this causes the current through the diode of
the opto-coupler to rise. The transistor of the opto-coupler
FM24
Supply
S
Capacitive
Z
Lr
Cr
Ri
) and power. The load is
S_UNSW
is mixed into the feedback voltage, using an
supply varies according the
S
= 70 + (10 * V
). Via this stabilisation
S
RS
, the output voltage is stabilised (if necessary, it
S
decreases.
S
9.
EN 93
Inductive
f
f
r
CL 16532099_110.eps
260901
), at the right side
R
, a control signal
RS
supply.
S
S
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