TCL SY33, Руководство по обслуживанию

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2003 Sep 09 11
Philips Semiconductors Product specification
GreenChip

II SMPS control IC
TEA1506P; TEA1506AP;
TEA1506T; TEA1506AT
Control pin protection
If pin CTRL is open-circuit or not connected, a fault
condition is assumed and the converter will stop switching.
Operation will recommence as soon as the fault condition
is removed.
Soft start-up
To prevent transformer rattle during hiccup, the
transformer peak current is slowly increased by the soft
start function. This can be achieved by inserting a resistor
and a capacitor between pin I
sense
and the sense resistor
(see Fig.11). An internal current source charges the
capacitor to V = I
SS
×
R
SS
, with a maximum of
approximately 0.5 V.
The start level and the time constant of the increasing
primary current level can be adjusted externally by
changing the values of R
SS
and C
SS
.
The charging current I
SS
will flow as long as the voltage on
pin I
sense
is below approximately 0.5 V. If the voltage on
pin I
sense
exceeds 0.5 V, the soft start current source will
start limiting the current I
SS
. At the V
CC(start)
level, the I
SS
current source is completely switched off.
Since the soft start current I
SS
is supplied from pin DRAIN,
the R
SS
value will not affect the V
CC
current during start-up.
Driver
The driver circuit to the gate of the power MOSFET has a
current sourcing capability of 135 mA typical and a current
sink capability of 560 mA typical. This permits fast turn-on
and turn-off of the power MOSFET for efficient operation.
A low driver source current has been chosen to limit the
∆
V/
∆
t at switch-on. This reduces Electro Magnetic
Interference (EMI) and also limits the current spikes
across R
sense
.
I
primary(max)
V
ocp
I
SS
R
SS
× ( )
–
R
sense
----------------------------------------------- =
τ
R
SS
C
SS
×
=
handbook, halfpage
CSS
RSS
Isense
Rsense
ISS
Vocp
start-up
MGU237
5
0.5 V
Fig.11 Soft start.