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,;<
5. DESCRIPTION OF OPERATION ,;:
5-1 SWITCHING MODE POWER SUPPLY CIRCUIT
-
.
The
TDA4601
is designed for driving controlling and
protecting
the
s~itching
transistor in flyback converter power supplIes during start-up
~ormal
and overload operation as well as during disturded operation . In
case
of disturbance the drive of the switching transistor is
inhibited
and a secandary voltage rise IS prevented.
A. The
start-ur procedures include three consecutive operating phase as
follows:
1. aui ld-ur internal ref erence vol tage
The
intenal
reference voltage supplies the voltage
regulator and
effects charging of the coupling electrolytic capacitor cannected to
the switching transistor.
~
Enabling of internal voltage reference voltage Vl=4V
Simultaneously with va reaching approx 12V.
an Internal
voltage
becomes
available
providing all
component
elements.
with
the
exceptIon
of the control lOgIC with a thermally stable and overload
resistant current supply.
3. Enabl ing of control lagH
In conjunction with the generation of the reference
voltage.
The
current
supply
for the control lOgIC is activated by means
of
an
additional
stabilization circuit The Integrated circuit
is
then
ready for operation.
B. Normal operation mode/control operation mode
C.
At the input of Pin 2 the zero passage of the frequency provided by the
feedback
coil
~re
registered and forwarded to the control logic Pin 3
( control
input overload and standing
identification)
receives
the
~ectified
amplitude
fluctcations
of the feedback
coil the
control
amplifier
operates with an input voltage of approx 2V and a current of
a~prox
1.4mA depending on the internal voltage reference.
The
overload
identification
limits
in
conjunction with
collector
current
simulator Pin 4 the operating range of the
control
amplifier
The collctor current is sImulated by an external RC combinatIon present
at
Pin 4 and internally set threshold voltage
The
largest
possible
collector
current applIcable with the switching transistor increase in
propovtion to
~he
increased
~apactance
caos
thus the reguired operatIng
range of the control
arnplifie~
is established the range of control lies
b~tween
a
DC
voltage clamped at 2V and a
sa~tooth-snaped
rising
AC
voltage
WhICh can vary up to a max amplitude of 4V (reference voltage)
during
secondary
load reductlon the switching frequency is
increased
and.
Pin 5
~t
is possible to externally inhibit the operatlon of
the
Ie,
the outp;.it:1.t ?in 8 4i11 be Inhibited when volltage
of~Vref
-O.IV
are present at PIn 5.
A~d
the
bas~
current amplifler forwards the sawtooth-shaped V4 voltage
to
the output of Pin 6.
A current feedback with an external
resistor
R804
1S
present between Pin 8 and Pin 7,
the applIed value
of
the
resistor
determines the max amplItude of the base driv1ng current
for
the switching transistor.
Protective operation mode
The
base
current shut-down activated by the
outpu~
of
P i;l 7 to
l. 61,1 .
As
a result the
~r~~:sistor
1S
inhibited
T his protective
supply voltage a: Pin
9
reach'Os
a
va
lue~6.
7
5
control logic clamps
the
drive of
the
switching
measure is enabled if
the
V or if vol tage at .::;;:
Vre~
2
... ....
-.:
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