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U2043B Datasheet, PDF (4/10 Pages) TEMIC Semiconductors – Flasher, 30-mohm Shunt, Pilot Lamp to GND or V Batt | |||
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3.6 Lamp Outage Detection (Pin 7)
The lamp current is monitored via an external shunt resistor R3 and an internal comparator K1
with its reference voltage of typically 81 mV (VS = 12V). The outage of one lamp out of two
lamps is detected according to the following calculation:
Nominal current of 1 lamp: 21W/(VS = 12V):
Ilamp = 1.75A
Nominal current of 2 lamps: 2 Ã 21W/(VS = 12V): Ilamp = 3.5A
We recommend setting the detection threshold in the middle of the current range:
Ioutage â 2.7A
Thus, the shunt resistor is calculated as:
R3 = VT (K1)/Ioutage
R3 = 81 mV/2.7 A = 30 mâ¦
Comparator K1âs reference voltage is matched to the characteristics of filament lamps (see sec-
tion âControl Signal Thresholdâ).
The combination of the shunt resistor and the resistance of the wire harness prevents pin 7 from
a too high voltage in the case of shorted lamps.
3.7 Start Input (Pin 8)
Start condition for flashing:
The voltage at pin 8 has to be less than VS â 5V (flasher switch closed).
Humidity and dirt may decrease the resistance between 49a and GND. If this leakage resistance
is > 5 k⦠the IC is still kept in its off-condition. In this case the voltage at pin 8 is greater than
VS â 5V.
During the bright phase the voltage at pin 8 is above the K2 threshold, during the dark phase it is
below the K3 threshold. For proper start conditions a minimum lamp wattage of 10W is required.
4 U2043B
4720BâAUTOâ09/05
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