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From: Spehro Pefhany
Subject: Re: Voltage Reference With LM4041DIZ-ADJ
X-Newsreader: Forte Agent 1.92/32.572
Date: Tue, 24 Dec 2002 23:24:09 GMT
NNTP-Posting-Date: Tue, 24 Dec 2002 18:24:09 EST
On 24 Dec 2002 23:12:12 GMT, the renowned firstname.lastname@example.org (Ed
>I need a voltage reference for a resistive bridge circuit. I have a lm358
>comparator used to turn on a resistive load when a thermistor in the bridge
>falls below a preset value (about 2.5 volts).
>The circuit is run off of 5 volts and uses an LM2940T-5.0 regulator to supply
>the 5 volts necessary for the circuit. To increase the circuit accuracy I have
>used a 0.2 degree tolerance thermistor as the sensing element. The remaining
>resistors are in the bridge are 0.1 percent tolerance.
>I was going to use the unregulated DC voltage to power the voltage reference
>for the bridge. How do I increase the current capacity on the reference to
>allow it to power the resistive bridge circuit?
You shouldn't need any fancy reference, the LM2940 should be good
enough, provided it stays in regulation. You've got a ratiometric
circuit- the exact excitation voltage is unimportant. Worry more about
self-heating effects (you're operating in water, right?) and Vos of
your op-amp comparator, which could be as much as 5 mV.
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