U243B datasheet(2/6 Pages) TEMIC

2 / 6 page

U243B

TELEFUNKEN Semiconductors

Rev. A1, 05-Sep-96

Preliminary Information

2 (6)

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 Rt and Ct, and

the frequency can be calculated from

1.5

(Hz)

where f1 is the frequency in normal flashing operation

(basic frequency). The control frequency f2 is typically

2.2 times the value of f1 and is the frequency in the case

of lamp failure. The bright periods for f1 and f2 are inter-

nally set in the IC and are 50% for f1 and 40% for f2.

The resistors R1 and R2 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 R1,

R2 and the resistance of the coil of the relay. A current of

about 150 mA would then flow over R1, 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, R3. The circuit is not damaged by

such a short circuit.

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

VS = 12 V.

With 81 mV and a measuring resistance of R3 = 30 m

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 Rp ≥ 5 k

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 VS to Pin 6 is lower than that to Pin 2.

Defined operation is ensured with a lamp load of

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

Symbol

Value

Unit

Supply voltage

Pins 2 and 6

16.5

Surge forward current

tp = 0.1 ms

Pins 2 and 6

IFSM

1.5

tp = 2 ms

Pins 2 and 6

IFSM

1.0

tp = 2 ms

Pin 8

IFSM

Output current

Pin 3

0.3

Power dissipation

Tamb = 95°C

DIP8

Ptot

420

SO8

Ptot

340

Tamb = 60°C

DIP8

Ptot

690

SO8

Ptot

560

Junction temperature

150

°C

Ambient temperature range

Tamb

–40 to +95

°C

Storage temperature range

Tstg

–55 to +125

°C

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