ACPL-782T Ver la hoja de datos (PDF) - Avago Technologies
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ACPL-782T Datasheet PDF : 18 Pages
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Isolated Temperature Sensing using Thermistor
Thermistor is widely used to measure temperatures in
most systems application. A galvanic isolation between
the potential of the Thermistor and that of the analog-
to-digital is often required when they are mounted in
locations such as high voltage potential, electrically noisy
environments, poorly grounded environments, where
lack of isolation causes either safety or EMI issues.
RL = R1//(R2+R3)=R1(R2+R3)/(R1+R2+R3)
R2 and R3 divides the voltage across RL so that the voltage
fed into ACPL-782T does not exceed +200 mV. The high
impedance characteristic of the input terminals of ACPL-
782T helps in determining those resistors value since one
can select relatively high resistance of R2 and R3 and R1
can be determined easily.
If R2+R3 >> R1, RL ~ R1
Dividing ratio ~ R3/(R2+R3)
As can be seen from the circuit, one might eliminate R1
and RL~(R2+R3) in this case.
An application example with a Thermistor designed for
measuring IGBT’s surface temperatures is shown in Figure
23. Where TH is the thermistor and the RL is a resistor for
linearization. Suitable RL value is determined from the
Thermistor characteristic and the temperature range to
measure. Please note that the RL value is the compound
value of R1, R2 and R3.
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Data subject to change. Copyright © 2005-2011 Avago Technologies. All rights reserved.
AV02-1565EN - March 23, 2011
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