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LM1042N View Datasheet(PDF) - National ->Texas Instruments

Part NameLM1042N National-Semiconductor
National ->Texas Instruments National-Semiconductor
DescriptionFluid Level Detector
LM1042N Datasheet PDF : 8 Pages
1 2 3 4 5 6 7 8
Application Notes (Continued)
FIGURE 9
TL H 8709 – 12
PROBE CURRENT REFERENCE CIRCUIT
The circuit defining the probe circuit is given in Figure 10 A
reference voltage is obtained from a bandgap regulator de-
rived current flowing in a diode resistor chain to set up a
voltage 2 volts below the supply This is applied to an ampli-
fier driving an external PNP transistor to maintain pin 3 at 2V
below supply The emitter resistance from pin 3 to supply
defines the current which less the base current flows in the
probe Because of the sensitivity of the measurement to
probe current evident in Figure 3 the current should be ad-
justed by means of a variable resistor to the desired value
This adjustment may also be used to take out probe toler-
ances
FIGURE 10
TL H 8709 – 13
TYPICAL APPLICATIONS CIRCUIT
A typical automotive application circuit is shown in Figure 11
where the probe selection signal is obtained from the oil
pressure switch At power up (ignition on) the oil pressure
switch is closed and pin 8 is held low by R4 causing a probe
1 (oil level) measurement to be made Once the engine has
started the oil pressure switch opens and D1 pulls pin 8 high
changing over to the second auxiliary probe input The ca-
pacitor C5 holds pin 8 high in the event of a stalled engine
so that a second probe 1 measurement can not occur in
disturbed oil Non-automotive applications may drive pin 8
directly with a logic signal
FIGURE 11 Typical Application Circuit
TL H 8709 – 14
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