TDA8385 Philips Semiconductors, TDA8385 Datasheet - Page 4

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

Philips Semiconductors
PINNING
FUNCTIONAL DESCRIPTION
The TDA8385 can be divided into
10 functional blocks as shown in Fig.1
and Fig.2.
Block for Figs 1 and 2
These 10 functional blocks of Fig.1
and Fig.2 contain sub-sections
numbered 1 to 28 which are
March 1994
RIO
LED
I
T
I
DELAY
V
OVP
V
V
V
I
V
GND
DEM
V
I
II
III
IV
V
VI
VII
VIII
IX
X
BLOCK
ref
peak
sim
on(min)
ss
fb
sb
diff
fo
P
Control circuit for a Self-Oscillating
Power Supply (SOPS)
NO.
SYMBOL
supply references
sawtooth generator
control part
pulse width modulator
(PWM)
LED control
LED driver
slow-start circuitry
over-voltage protection
stand-by circuit
regulation-indicator
output
DESCRIPTION
PIN
10
11
12
13
14
15
16
1
2
3
4
5
6
7
8
9
regulation indicator output
LED driver output
current reference setting
transistor-on setting input
peak current setting input
delay setting
slow start voltage input
over-voltage protection
feedback voltage input
stand-by voltage input
differential amplifier output
current simulation input
feed forward input
ground (0 V)
demagnetization input
positive supply voltage
cross-referenced in the following
description.
Supply references (Block I)
The TDA8385 is intended to be used
on the secondary side of the
self-oscillating power supply. It can be
supplied either by an auxiliary winding
of the transformer or an external
supply e.g. 50 Hz transformer.
Charging of the capacitor C
Fig.16) takes place during transistor
on-time (T
stand-by the IC is supplied by the
stand-by voltage V
operating voltage range is from 7.5 to
20 V. The supply current, inclusive
drive current for the LED, is less than
20 mA. A bandgap based reference
(2.5 V) generates a stabilized voltage
V
circuits of the IC except the LED
driver. The LED driver is directly
supplied by V
generates all the reference voltages
in the circuit. By means of a resistor
connected to pin 3, a reference
current (I
stab
of 3.9 V to supply all internal
DESCRIPTION
ref
on
) is defined.
; see Fig.17). During
P
. The reference block
5
sb
(pin 10). The
P
(see
handbook, 2 columns
This current is reflected several times
and is used to obtain IC-independent
settings e.g. T
setting, charging and discharging of
slow-start capacitor C
(see Fig.16).
The power supply is released by the
opto-coupler IC at an input voltage
level, which is high enough to
guarantee correct operation of the
TDA8385 e.g. V
the mains voltage V
SOPS switching transistor (T1, see
Fig.16) is conductive the capacitor C
is charged. As long as the IC supply
voltage is below 7.5 V the LED driver
is blocked (see latch output;
sub-section 28) in order to guarantee
start-up of SOPS.
During the initialization phase the
quick-discharge-switch
(sub-section 27), set input of
flip-flop (13) and reset input of
flip-flop (23) are also activated.
As soon as the voltage of 7.5 V is
reached the control functions of the IC
are operative. Hysteresis on the
initialization level is 2.3 V.
T on(min)
DELAY
I peak
OVP
LED
RIO
I ref
V ss
Fig.3 Pinning diagram.
1
3
4
2
5
6
7
8
Preliminary specification
on(min)
TDA8385
P
= 10 V by sensing
I
MCD402
. As soon as the
TDA8385
setting, delay
ss
on pin 7
16
15
14
13
12
11
10
9
V P
DEM
GND
V fo
I sim
V diff
V
V
sb
fb
P