March 1994

Philips Semiconductors

Preliminary specification

Control circuit for a Self-Oscillating
Power Supply (SOPS)

TDA8385

FEATURES

Bandgap reference generator

Slow-start circuitry

Low-loss peak current sensing

Over-voltage protection

Hysteresis controlled stand-by
function

Error amplifier with gain setting

Programmable transfer character
generator

Protection against open- and
short-circuited feedback loop

Over-load current fold back
characteristic

LED driver

Demagnetization protection

Programmable determination of
switch-on moment of switching
transistor for low-switching losses

Feed-forward input

Regulation-indicator output

Programmable minimum on-time of
switching transistor

Accurate peak-current setting.

GENERAL DESCRIPTION

The TDA8385 is intended to be used
in combination with the opto-coupler
(CNR50) as a control unit for a
self-oscillating power supply.

ORDERING INFORMATION

EXTENDED TYPE

NUMBER

PACKAGE

PINS

PIN POSITION

MATERIAL

CODE

TDA8385

DIL

plastic

SOT38WBE

March 1994

Philips Semiconductors

Preliminary specification

Control circuit for a Self-Oscillating
Power Supply (SOPS)

TDA8385

BLOCK DIAGRAMS

handbook, full pagewidth

MCD417

V ts

DIFFERENTIAL AMPLIFIER

CONTROL PART

REGULATION

INDICATOR

(2.5 V)

reset (28)

quick

discharge

CLAMP

charge

2.5 V

TCG

V TCG

V diff

Vss +

MINIMUM

VOLTAGE

CLAMP

III

VII

Vmv

RIO

11 V diff

Vss

REFERENCE

BLOCK

STABILIZED

SUPPLY

DETECTOR

VP (min)

SUPPLY REFERENCES

(28, 27, 23)

reset

latch

I ref

Vstab

Vref

current reference

setting

feed forward

input

regulation indicator

output

differential amplifier

output

slow start voltage

input

feedback voltage

input

transistor-on

setting input

GND

SLOW START

V ts

Ton(min)

Ton (min)

Fig.1 Block diagram; part A (continued in Fig.2; part B).

March 1994

Philips Semiconductors

Preliminary specification

Control circuit for a Self-Oscillating
Power Supply (SOPS)

TDA8385

handbook, full pagewidth

stand-by voltage input

over-voltage

protection

latch

MCD418

100

slow

discharge

(17)

(28)

VIII

over voltage

115 mV

2.5 V

OVER-VOLTAGE PROTECTION

DELAY

115 mV

100 mV

SAWTOOTH GENERATOR

DEM

Vsb

Vsim

PWM

demagnetization

LED CONTROL

demagnetization

(28)

I12

0.2 I

I sim

I peak

2.5 V

2 V

STAND-BY

2.5 V

latch

Q (23)

OUTPUT

STAGE

LED

LED DRIVER

TDA8385

LED driver output

delay setting

demagnetization

input

peak-current

setting input

current simulation

input

comparator

Fig.2 Block diagram; part B (continued from Fig.1; part A).

March 1994

Philips Semiconductors

Preliminary specification

Control circuit for a Self-Oscillating
Power Supply (SOPS)

TDA8385

PINNING

SYMBOL

PIN

DESCRIPTION

RIO

regulation indicator output

LED

LED driver output

ref

current reference setting

on(min)

transistor-on setting input

peak

peak current setting input

DELAY

delay setting

slow start voltage input

OVP

over-voltage protection

feedback voltage input

stand-by voltage input

diff

differential amplifier output

sim

current simulation input

feed forward input

GND

ground (0 V)

DEM

demagnetization input

positive supply voltage

Fig.3 Pinning diagram.

handbook, 2 columns

RIO

LED

DELAY

OVP

I ref

Ton(min)

I peak

Vss

DEM

GND

Vfo

I sim

Vdiff

TDA8385

MCD402

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

BLOCK

NO.

DESCRIPTION

supply references

sawtooth generator

III

control part

pulse width modulator
(PWM)

LED control

LED driver

VII

slow-start circuitry

VIII

over-voltage protection

stand-by circuit

regulation-indicator
output

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

(see

Fig.16) takes place during transistor
on-time (T

; see Fig.17). During

stand-by the IC is supplied by the
stand-by voltage V

(pin 10). The

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

stab

of 3.9 V to supply all internal

circuits of the IC except the LED
driver. The LED driver is directly
supplied by V

. The reference block

generates all the reference voltages
in the circuit. By means of a resistor
connected to pin 3, a reference
current (I

ref

) is defined.

This current is reflected several times
and is used to obtain IC-independent
settings e.g. T

on(min)

setting, delay

setting, charging and discharging of
slow-start capacitor C

on pin 7

(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

= 10 V by sensing

the mains voltage V

. As soon as the

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.

March 1994

Philips Semiconductors

Preliminary specification

Control circuit for a Self-Oscillating
Power Supply (SOPS)

TDA8385

Fig.4 Latch initialization as a function of supply voltage V

5.2

7.5

latch

initialization

operation

VP (V)

MCD403

Sawtooth generator (Block II)

URRENT SIMULATION

(

SEE FIGS

AND

16)

The current of the power supply
switching transistor is detected on the
secondary side by an indirect method
of current sensing.

Information of the collector current (I

)

is obtained by integrating the voltage
of an auxiliary winding of the
transformer during transistor on-time
(T

). An external capacitor C on pin 5

is charged during T

by the current

source I

sim

. The current I

sim

is the

reflection of the current which flows
into pin 12. This current is obtained by
connecting an external resistor R12 to
the auxiliary transformer winding.
During transistor on-time this current
is related to the input voltage V

During transistor off time (T

off

) the

capacitor C is discharged by switch
sw1. This switch is active during the
total T

off

time. In this way a sawtooth

voltage V

is formed across C. This

sawtooth is a measure for the
collector current of the switching
transistor T1.

For the voltage V

yields:

(1)

(2)

Where: p = reflection factor;

(2)

(1) gives:

(3)

sim

-------------------------

sim

------

R12

-----------

sim

---------

0.2

----

------

R12

-----------

Fig.5 Determination of the peak current I

handbook, full pagewidth

R12

I 12

Isim

n p

n h

MCD404

Ton

Toff

sw1

March 1994

Philips Semiconductors

Preliminary specification

Control circuit for a Self-Oscillating
Power Supply (SOPS)

TDA8385

For `T

' yields:

(4)

For the primary current I

yields:

(5)

Substitution (4) into (5):

(6)

Equation (6) shows that by limiting the
voltage V

the collector peak current

can be limited. The peak current is
limited by means of the clamping
circuit in the transfer character
generator (TCG); see Fig.1
sub-section 4.

The clamping level can be externally
influenced by means of a resistor
on pin 7.

The collector peak current can be
influenced in several ways:

Resistor R12 on pin 12

Capacitor C on pin 5

Capacitor on pin 7

Transfer ratio n

Inductance L

Before comparing the sawtooth
voltage V

with the control voltage V

in the pulse width modulator, a
voltage of 100 mV is added to V

. In

this way it will be possible for V

become smaller than V

sim

, which is

important for a stabilized no-load
operation (see Fig.6 area 3).

EMAGNETIZATION INPUT

(

15)

This input prevents the switching
transistor from conducting during
demagnetization of the transformer in
order to prevent the transformer from
going into saturation. The output of
comparator (11) is HIGH as soon as
the voltage of the transformer winding
exceeds 115 mV.

R12

-----------------------------------------------

-----

----

1
p

---

------

R12

ELAY SETTING

(

The output of sub-section 11 is
extended by the delay circuit of
sub-section 12. The starting
(reference) point of the delay circuit is
the falling edge of the output of
demagnetizing comparator (11) The
delay can be determined externally by
capacitor (C

delay

) on pin 6.

The switch-on moment of the
switching transistor can be
determined by capacitor C

delay

A minimum delay time is required to
prevent transistor T1 from switching
during demagnetization of the
transformer because of oscillations
caused by the leakage inductance.

Control part (Block III)

The differential amplifier,
sub-section 3, compares the
feedback voltage (V

) with the

reference voltage V

ref

. The output of

the differential amplifier is available
on pin 11 to allow gain setting. The
differential amplifier is internally
compensated for 0 dB feedback
stability.

The feedback input (pin 9) is also
used as the input for the TCG
(see Fig.6) with which a current
foldback characteristic can be
obtained as shown in Fig.7.

Fig.6 Reference voltage (V

) as a function of feedback voltage (V

(1), (2), (3) = V

TCG

(4), (5) = V

diff

(5)

(4)

(3)

(2)

(1)

MCD405

Vmv

VTon(min)

Vclamp

March 1994

Philips Semiconductors

Preliminary specification

Control circuit for a Self-Oscillating
Power Supply (SOPS)

TDA8385

Fig.7

Current foldback characteristic; stabilized output voltage (V

)

as function of load current (I

(5)

(4)

(3)

(2)

(1)

MCD406

(1), (2), (3) = V

TCG

(4), (5) = V

diff

The voltage V

Ton(min)

determines the

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.

Stand-by operation

Starting-up of power supply

Overload and short-circuit
conditions.

The output of the differential amplifier
(V

diff

), the output of the TCG (V

TCG

)

and the voltage V

+ V

Ton(min)

are

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.

Fig.8 Characteristics of the control part.

The voltage V

determines the collector peak current I

of transistor T1. The right-hand curve is passed through at start-up. When the feedback voltage

slowly increases from zero, the peak current starts at I

c(min)

and rises along the straight line until I

c(max)

is reached. At a slightly higher feedback voltage

the regulation slope is reached, which is approximately V

ref

The plateau of the top between the points x and y has to be kept as small as possible.

The voltage V

diff

decreases with the decreasing load. For good no-load operation the peak current has to be made zero with V

diff

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

. This input can be used for feed forward information.

If no feed forward information is used, pin 13 should be connected to ground.

handbook, full pagewidth

MCD407

Vss +

Ic (max)

Ic (min)

Vmv

Vref

VTCG

external peak-current
setting (pin 7)

diff

VTon(min)

March 1994

Philips Semiconductors

Preliminary specification

Control circuit for a Self-Oscillating
Power Supply (SOPS)

TDA8385

Pulse width modulator (Block IV)

The pulse width modulator compares
the control voltage V

with the

sawtooth voltage V

sim

. If V

sim

output sub-section 8 is HIGH the LED
is switched on and then the switching
transistor is switched off. In this way
the output voltage is controlled.

XAMPLE

If the load decreases, V

increases

and therefore V

decreases. This

causes the LED to start conducting
prematurely, which implies that the
switching transistor is turned off
sooner. The consequence is that the
collector peak current decreases and
hence less energy is stored in the
transformer and V

will decrease.

LED control (Block V)

If either output of sub-section 8 or
output of sub-section 16 are HIGH the
LED is conductive. In order to
improve the start-up behaviour of the
power supply, the demagnetization
signal of sub-section 12 will only
activate the LED driver if flip-flop (13)
has previously been set. The set
signal is generated in the following
three ways.

1. Pulse width modulator

(sub-section 8)

2. Comparator (18)

3. V

P(min)

detector

Set signal (2.) and (3.) are added as
extra security to guarantee a
demagnetization pulse in the event of
the switching transistor not having
enough base current. In that situation
e.g. at start-up, no comparator signal,
set signal (3.) is generated by
sub-section 8.

LED driver (Block VI)

The LED driver (pin 2) is blocked if the
supply voltage V

is in the

initialization phase (see Fig.4). The
output stage is a push-pull stage,
which can sink 5 mA and source
10 mA.

Slow-start circuit (Block VII)

The slow-start circuit is active at
start-up, over voltage protection or
after an overload (short-circuited),
and stand-by mode. The voltage V

and therefore the voltage V

and the

peak current I

slowly increase at

start-up.

By means of sub-section 27 the slow
start voltage V

is clamped to the

voltage V

. If the feedback voltage is

reduced, e.g. as overload, the
slow-start capacitor is discharged to
the level of V

. In this way a slow

start-up is also guaranteed after an
overload, short-circuit situation or
after a stand-by mode. The circuit of
sub-section 27 is not active during an
over voltage protection.

When the supply voltage V

is below

the reset-level of 5.2 V
(sub-section 28) the slow-start
capacitor is quickly discharged.

The slow-start input (pin 7) can also
be used for I

c(max)

setting by

connecting a resistor to this pin.

Over voltage protection
(Block VIII)

The operation of the over voltage
protection circuit is, in the event of the
IC being SOPS-supplied, quite
different from when the IC is
externally supplied.

PERATION WHEN THE

EXTERNALLY SUPPLIED

When the voltage on pin 8 exceeds
2.5 V the slow-start capacitor is
slowly discharged. During discharge
the LED is permanently conducting.
Discharge is stopped when V

below 115 mV. Flip-flop (23) will then
be reset and the circuit is ready again
for a new slow-start procedure.

During an over voltage sub-section 27
is not active so that the output voltage
V

cannot influence the slow-start

discharge procedure.

PERATION WHEN

SOPS-

SUPPLIED

(

SEE FIGS

AND

10)

When the voltage on pin 8 exceeds
2.5 V the slow-start capacitor is
slowly discharged. During discharge
of C

the supply capacitor C

is also

discharged. Because the capacitors
C

and C

have almost the same

value and the supply current I

(

15 mA) is much larger than the slow

discharge current (

A), the LED

will be switched off by means of the
V

P(min)

detection circuit (5.2 V). At that

moment the switching transistor will
be switched on again until the 7.5 V
level is reached. During this
hysteresis interval the slow-charge
capacitor is quickly discharged. At the
7.5 V level the LED will be switched
on again because flip-flop (23) output
is still HIGH.

The same procedure will be repeated
several times until the slow-start
capacitor reaches the 115 mV reset
level. At that moment the slow-start
procedure is started again.

If there is still an over voltage the
procedure will be repeated.

Figure 10 is a detailed exposure of
Fig.11.

March 1994

Philips Semiconductors

Preliminary specification

Control circuit for a Self-Oscillating
Power Supply (SOPS)

TDA8385

LIMITING VALUES

In accordance with the Absolute Maximum Rating System (IEC 134).
All voltages are measured with respect to ground; positive current flow into the IC; all pins not mentioned in the voltage
list are not allowed to be voltage driven. The voltage ratings are valid provided other ratings are not violated; current
ratings are valid provided the power rating is not violated.

THERMAL RESISTANCE

SYMBOL

PARAMETER

CONDITIONS

MIN.

MAX.

UNIT

Voltages

supply voltage

pin 2 connected

0.5

pin 2 open-circuit

0.5

voltage on pins 1, 2, 4, 7, 9 and 13

0.5

+18

voltage on pin 3

0.5

8,10

voltage on pins 8 and 10

0.5

+3.9

voltage on pin 12

0.1

+0.5

voltage on pin 15

0.5

+0.5

Currents

current on pin 1

current on pins 2, 12 and 15

+10

current on pin 3

5, 6

current on pins 5 and 6

current on pin 7

+25

current on pin 11

+0.5

current on pin 16

Temperatures

amb

operating ambient temperature

+70

stg

storage temperature

+150

Power dissipation

tot

total power dissipation

500

SYMBOL

PARAMETER

THERMAL RESISTANCE

th j-a

from junction to ambient in free air

55 K/W

March 1994

Philips Semiconductors

Preliminary specification

Control circuit for a Self-Oscillating
Power Supply (SOPS)

TDA8385

CHARACTERISTICS

= 15 V; I

= 200

A; T

amb

= 25

C; unless otherwise specified.

SYMBOL

PARAMETER

CONDITIONS

MIN.

TYP.

MAX.

UNIT

Supply

supply voltage (pin 16)

7.9

supply initialization level

7.1

7.5

7.9

16(hys)

internal fixed hysteresis

2.5

2.55

supply current

active LED output

supply voltage ripple rejection

see Figs 13 and 14

Reference voltage

reference voltage at pin 3

0.52

0.55

0.58

Error amplifier

threshold voltage error amplitude

2.4

2.5

2.6

input current feedback input

0.5

sink current output

= 80 mV

400

source current output

= 2.5 V

500

open loop gain

100

unity gain bandwidth

600

kHz

temperature coefficient

300

threshold for switching output

diff

= 1.25 V;

= 2 V; V

= 0 V;

; I

= 2 mA

diff

(1)

Transfer characteristic generator

current ratio

= 0.5 V

0.23

0.25

0.27

threshold for switching output

= 0.5 V; V

= 0 V;

; I

= 2 mA

on(min)

= 0 V

0.4

0.5

0.6

= 20%

= 0.4 V

0.9

= 50%

= 1 V

1.4

1.5

1.6

= 80%

= 1.6 V

2.1

clamp

= 2.25 V

2.4

2.6

PLH

response time pulse width
modulation pin 5 to pin 2
LOW-to-HIGH

note 2

700

PHL

response time pulse width
modulation pin 5 to pin 2
HIGH-to-LOW

note 2

Feed forward

threshold for switching output
(V

)

= 0.5 V; V

= 0 V;

= V

= 3 V;

= 2 mA; V

= 1 V

0.6

0.7

0.8

input bias current

= 0 V

March 1994

Philips Semiconductors

Preliminary specification

Control circuit for a Self-Oscillating
Power Supply (SOPS)

TDA8385

Slow-start

charge current ratio

= 0.5 V

0.22

0.24

0.26

quick discharge current

= 1 V

= 100 mV

clamping level

= 100

2.8

3.0

3.2

threshold for switching output
(V

)

= 0.5 V; V

= 0 V;

= 1 V; I

= 2 mA;

= 2 V

1.4

1.5

1.6

Output stage

2(sat)

saturation voltage

= 2 mA

300

source current

= 2 V

operating

4.8

5.3

6.3

initialization phase

open output voltage HIGH

= 5 mA

Current simulation

current ratio

= 1 V; I

= 0.5 mA 0.19

0.2

0.21

simulation input voltage

= 0.5 mA

1.1

5(sat)

saturation voltage

= V

= 0 V;

= 1 mA

300

= V

= 0 V;

= 200

200

threshold for switching output;
voltage difference between pins 5
and 11; offset simulation voltage
(V

)

= 0.5 V; V

= 0 V;

= V

= 3 V;

= 2 mA;

= 0.5 V

100

140

Demagnetization input

demLH

delay from pin 15 to pin 5
LOW-to-HIGH

see Fig.15;
pin 6 not connected

500

demHL

delay from pin 15 to pin 5
HIGH-to-LOW

see Fig.15

clamping level

= 10 mA

positive

1.2

negative

demagnetization threshold
voltage

115

140

input capacitance

input bias current

= 60 mV

0.5

SYMBOL

PARAMETER

CONDITIONS

MIN.

TYP.

MAX.

UNIT

March 1994

Philips Semiconductors

Preliminary specification

Control circuit for a Self-Oscillating
Power Supply (SOPS)

TDA8385

Notes

1. V

= V

offset.

2. V

pulse = 1 V; V

= 0.5 V; V

= V

= 3 V; V

= 0.5 V; V

= 0 V; I

= 2 mA.

Delay setting

charge current ratio

= 1 V

1.1

1.2

1.3

charge current initialization phase V

= 1 V; V

= 5 V

clamping level

2.8

3.2

6(sat)

saturation voltage

= 140 mV

100

dLH

delay from pin 6 to pin 2;
V

crossing the 2.5 V level;

LOW-to-HIGH

= 470 pF;

= 0 V; I

= 2 mA;

see Fig.15;

excluding capacitive
tolerances

1.2

t/c

delay setting (t = C

V/I)

= 2.5 V;

= 250

ns/pF

Stand-by

10H

threshold level HIGH

2.4

2.5

2.6

10(hys)

hysteresis

450

500

550

dLH

delay to output pin 10 to pin 2
LOW-to-HIGH

dHL

delay to output pin 10 to pin 2
HIGH-to-LOW

input current

= 2.3 V

Over voltage protection

threshold level

2.4

2.5

2.6

dLH

delay to output pin 8 to pin 2
LOW-to-HIGH

dHL

delay to output pin 8 to pin 2
HIGH-to-LOW

reset level

140

slow discharge current ratio

= 1 V

0.12

0.23

0.31

input current

= 3 V

Regulation indicator output

saturation voltage

= 1 mA

300

leakage current

= V

SYMBOL

PARAMETER

CONDITIONS

MIN.

TYP.

MAX.

UNIT

March 1994

Philips Semiconductors

Preliminary specification

Control circuit for a Self-Oscillating
Power Supply (SOPS)

TDA8385

SOLDERING

Plastic dual in-line packages

Y DIP OR WAVE

The maximum permissible
temperature of the solder is 260

this temperature must not be in
contact with the joint for more than
5 s. The total contact time of
successive solder waves must not
exceed 5 s.

The device may be mounted up to the
seating plane, but the temperature of
the plastic body must not exceed the
specified storage maximum. If the
printed-circuit board has been
pre-heated, forced cooling may be
necessary immediately after
soldering to keep the temperature
within the permissible limit.

EPAIRING SOLDERED JOINTS

Apply a low voltage soldering iron
below the seating plane (or not more
than 2 mm above it). If its temperature
is below 300

C, it must not be in

contact for more than 10 s; if
between 300 and 400

C, for not

more than 5 s.

DEFINITIONS

LIFE SUPPORT APPLICATIONS

These products are not designed for use in life support appliances, devices, or systems where malfunction of these
products can reasonably be expected to result in personal injury. Philips customers using or selling these products for
use in such applications do so at their own risk and agree to fully indemnify Philips for any damages resulting from such
improper use or sale.

Data sheet status

Objective specification

This data sheet contains target or goal specifications for product development.

Preliminary specification

This data sheet contains preliminary data; supplementary data may be published later.

Product specification

This data sheet contains final product specifications.

Limiting values

Limiting values given are in accordance with the Absolute Maximum Rating System (IEC 134). Stress above one or
more of the limiting values may cause permanent damage to the device. These are stress ratings only and operation
of the device at these or at any other conditions above those given in the Characteristics sections of the specification
is not implied. Exposure to limiting values for extended periods may affect device reliability.

Application information

Where application information is given, it is advisory and does not form part of the specification.

Ð­Ð»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: TDA8385

ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: TDA8385