TCL SY33, Руководство по обслуживанию

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2003 Sep 09 8
Philips Semiconductors Product specification
GreenChip

II SMPS control IC
TEA1506P; TEA1506AP;
TEA1506T; TEA1506AT
Demagnetization
The system will be in discontinuous conduction mode all
the time. The oscillator will not start a new primary stroke
until the secondary stroke has ended.
Demagnetization features a cycle-by-cycle output
short-circuit protection by immediately lowering the
frequency (longer off-time), thereby reducing the power
level.
Demagnetization recognition is suppressed during the first
t
suppr
time. This suppression may be necessary in
applications where the transformer has a large leakage
inductance, at low output voltages and at start-up.
If pin DEM is open-circuit or not connected, a fault
condition is assumed and the converter will stop operating
immediately. Operation will recommence as soon as the
fault condition is removed.
Minimum and maximum ‘on-time’
The minimum ‘on-time’ of the SMPS is determined by the
Leading Edge Blanking (LEB) time. The IC limits the
‘on-time’ to 50
µ
s. When the system desires an ‘on-time’
longer than 50
µ
s, a fault condition is assumed (e.g.
removed C
i
in Fig.12), the IC will stop switching and enter
the safe restart mode.
OverVoltage Protection (OVP)
An OVP mode is implemented in the GreenChip series.
This works for the TEA1506 by sensing the auxiliary
voltage via the current flowing into pin DEM during the
secondary stroke. The auxiliary winding voltage is a
well-defined replica of the output voltage. Any voltage
spikes are averaged by an internal filter.
If the output voltage exceeds the OVP trip level, an internal
counter starts counting subsequent OVP events. The
counter has been added to prevent incorrect OVP
detections which might occur during ESD or lightning
events. If the output voltage exceeds the OVP trip level a
few times and not again in a subsequent cycle, the internal
counter will count down with twice the speed compared
with counting-up. However, when typical 10 cycles of
subsequent OVP events are detected, the IC assumes a
true OVP and the OVP circuit switches the power
MOSFET off. Next, the controller waits until the UVLO
level is reached on pin V
CC
. When V
CC
drops to UVLO,
capacitor C
VCC
will be recharged to the V
start
level.
Regarding the TEA1506, the IC will not start switching
again. Subsequently, V
CC
will drop again to the UVLO
level, etc.
Operation only recommences when the V
CC
voltage drops
below a level of about 4.5 V.
Regarding the TEA1506A, when the V
start
level is reached,
switching starts again (safe restart mode) when the V
start
level is reached. This process is repeated as long as the
OVP condition exists.
The output voltage V
o(OVP)
at which the OVP function trips,
can be set by the demagnetization resistor, R
DEM
:
where N
s
is the number of secondary turns and N
aux
is the
number of auxiliary turns of the transformer.
Current I
(OVP)(DEM)
is internally trimmed.
The value of R
DEM
can be adjusted to the turns ratio of the
transformer, thus making an accurate OVP possible.
V
o OVP
( )
N
s
N
aux
----------- I
(OVP)(DEM)
R
DEM
×
V
clamp(DEM)(pos)
+
{ }
=