TDA8385 Philips Semiconductors, TDA8385 Datasheet - Page 7

• Manufacturer Part Number: TDA8385
• Description: Control circuit for a Self-Oscillating Power Supply SOPS
• Manufacturer: Philips Semiconductors

Philips Semiconductors
March 1994
Control circuit for a Self-Oscillating
Power Supply (SOPS)
(1), (2), (3) = V
(4), (5) = V
The voltage V
slowly increases from zero, the peak current starts at I
the regulation slope is reached, which is approximately V
The plateau of the top between the points x and y has to be kept as small as possible.
The voltage V
Due to the characteristic of the TCG open- and short-circuit feedback loop will result in low peak current.
An additional signal on pin 13 can be supplied which is subtracted from the signal V
If no feed forward information is used, pin 13 should be connected to ground.
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Fig.7
diff
.
Current foldback characteristic; stabilized output voltage (V
as function of load current (I
V
mv
diff
TCG
O
determines the collector peak current I
decreases with the decreasing load. For good no-load operation the peak current has to be made zero with V
.
V ss +
(5)
I c (max)
(1)
V Ton(min)
(4)
I c (min)
(2)
Fig.8 Characteristics of the control part.
O
).
I c
c(min)
c
of transistor T1. The right-hand curve is passed through at start-up. When the feedback voltage
ref
.
and rises along the straight line until I
V mv
(3)
I O
MCD406
8
x
mv
V
. This input can be used for feed forward information.
fb
y
O
V ref
)
c(max)
is reached. At a slightly higher feedback voltage
The voltage V
minimum on-time of the switching
transistor. This voltage can be
determined externally with a resistor
on pin 4. With this resistor the current
foldback characteristic can be
influenced (see dotted line in Figs 6
and 7).
The minimum on-time is of
importance for the following.
The output of the differential amplifier
(V
and the voltage V
compared in a minimum voltage
clamping circuit (see Fig.1
sub-section 6). The output voltage is
equal to the lowest input voltage.
Some relevant characteristics of the
control part are depicted in Fig.8.
MCD407
Stand-by operation
Starting-up of power supply
Overload and short-circuit
conditions.
diff
), the output of the TCG (V
V TCG
V
V
external peak-current
setting (pin 7)
diff
mv
Preliminary specification
Ton(min)
diff
.
ss
+ V
TDA8385
determines the
Ton(min)
are
TCG
)