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LL204

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

3 of 5

www.unisonic.com.tw

QW-R121-012.C



BLOCK DIAGRAM

Vcc-13mV

VRef1

VRef2

Vcc/2

4.7KΩ

R10

1.2KΩ

4.7KΩ

right

left

1.2KΩ

4.7KΩ

Relay

200Ω

Hazard warning

GND 10

27.5V

Vcc-6V

82KΩ

4.7μF

47KΩ

Vcc

Vstart

GND

RShunt

4.8mΩ

Contast

Vcc

5W 21W 21W

21W 21W 5W

Pin 8, Lamp outage detection

The lamp current is monitored via an external shunt resistor R3 and an internal comparator K1 with its reference

voltage of typ. 13 mV (VSS = 12V). The outage of one lamp out of two lamps is detected according to the following

calculation:

Nominal current of 1 lamp: 21W / (VSS = 12V): Ilamp = 1.75A

Nominal current of 2 lamps: 2 x 21W / (VSS = 12V): Ilamp = 3.5A.

The detection threshold is recommended to be set in the middle of the current range: Ioutage ≈ 2.7A.

Thus the shunt resistor is calculated as:

R3 = VT (K1) / Ioutage

R3 = 13mV/2.7A = 4.8mΩ.

Comparator K1‘s reference voltage is matched to the characteristics of filament lamps (see “control signal

threshold” in the data part).

The combination of shunt resistor and resistance of wire harness prevents Pin 8 from a too high voltage in case of

shorted lamps.

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