U243B
Circuit Description
The application circuit shows the operation of the U243B
as a car-direction indicator signal generator. The flashing
frequency is determined by the components R
t
and C
t
, and
the frequency can be calculated from
f
1
The use of this application circuit ensures damage and
interference protection accordance to VDE 0839. The
recognition point for lamp failure can be calculated from
the control signal threshold, typically 81 mV with
V
S
= 12 V.
1
R
t
C
t
1.5
(Hz)
where f
1
is the frequency in normal flashing operation
(basic frequency). The control frequency f
2
is typically
2.2 times the value of f
1
and is the frequency in the case
of lamp failure. The bright periods for f
1
and f
2
are inter-
nally set in the IC and are 50% for f
1
and 40% for f
2
.
The resistors R
1
and R
2
are needed to protect the circuit
against possible damage. An integrated Z-diode in addi-
tion to these external resistors limits the impulse current
in the integrated circuit to
≤
1.5 A. Connecting the circuit
with the wrong polarity leads to current limitation by R
1
,
R
2
and the resistance of the coil of the relay. A current of
about 150 mA would then flow over R
1
, so that for unlim-
ited protection against continuous reversal of the polarity
of the supply, a 2-W resistor would be necessary. A short
circuit between the indicator lamp (49a) and ground (31)
can give rise to a voltage drop of about 4 V across the
measuring resistance, R
3
. The circuit is not damaged by
such a short circuit.
With 81 mV and a measuring resistance of R
3
= 30 m
W
,
it corresponds to a lamp current of 2.7 A, i.e., the
frequency change-over with a lamp load of 21 W
+ 11.4 W. The variation of the control-signal threshold
with the supply voltage takes into account the PTC char-
acteristic of the filament lamps. A resistance R
p
≥
5 k
W
between the lamp indicator (49a) and ground (31) ensures
that in case the direction indicator switch is open, the
flashing generator is in stand-by mode.
With a control lamp of max. 4 W between 49 and 49a the
IC still starts with the bright phase.
The arrangement of the supply connections to Pins 2 and
6 must be such as to ensure that, on the connection PCB,
the resistance of V
S
to Pin 6 is lower than that to Pin 2.
Defined operation is ensured with a lamp load of
P
L
10 W or more. Defined operation with lamp loads
≥
2 W require an additional external resistance as
described in “Applications”. With considerably reduced
external circuitry, the integrated circuit U243B can be
used as an instable multivibrator in the frequency range
f = 0.05 to 10 Hz.
Absolute Maximum Ratings
Reference point Pin 1
Parameters
Supply voltage
Surge forward current
t
p
= 0.1 ms
t
p
= 2 ms
t
p
= 2 ms
Output current
Power dissipation
T
amb
= 95°C
T
amb
= 60°C
Junction temperature
Ambient temperature range
Storage temperature range
Pins 2 and 6
Pins 2 and 6
Pins 2 and 6
Pin 8
Pin 3
DIP8
SO8
DIP8
SO8
Symbol
V
S
I
FSM
I
FSM
I
FSM
I
o
P
tot
P
tot
P
tot
P
tot
T
j
T
amb
T
stg
Value
16.5
1.5
1.0
50
0.3
420
340
690
560
150
–40 to +95
–55 to +125
Unit
V
A
A
mA
A
mW
mW
mW
mW
°C
°C
°C
2 (6)
Preliminary Information
TELEFUNKEN Semiconductors
Rev. A1, 05-Sep-96
TEMIC [ TEMIC SEMICONDUCTORS ]
