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There's a LM741 OpAmp in a circuit, that's amplifying a signal (from a hall effect sensor) with about -0.5/+0.5 V voltage swing. The hall sensor requires about 1.2 V to operate.
Since I'm using a single power supply for the OpAmp (at ~10 V), I figured, that I need to shift the voltage to power the hall sensor up to about half the supply voltage, so that the sensor signal swings around Vcc/2.
The simplest way to do this, that came to mind, was to use a voltage divider with 3 resistors between Vcc/Gnd. Two big ones (R1) and a small one in between them (R2). According to this formula, I can pick up a voltage over R2 that is just in the middle between the power rails.
Something like that...
Vcc --- R1 --i-- R2 --i-- R1' --- Gnd
(Found by some simple calcs):
r = R1 / R2
r = ( Vcc - Vdiff ) / ( 2 * Vdiff )
example:
Vcc = 10 V
Vdiff = 1.2 V
r = ( 10 - 1.2 ) / ( 2 * 1.2 ) = 3.66...
So for R1 = 10 k, R2 = 36.6... k
The hall sensor doesn't require much power to work. So thought it should be ok to it that way, and in fact it does work, but isn't really stable somehow... Is this the proper way to do it (I actually don't think it is...)? Is there better still easy way to accomplish that? Maybe with two linear voltage regulators, like the LM317T?
Since I'm using a single power supply for the OpAmp (at ~10 V), I figured, that I need to shift the voltage to power the hall sensor up to about half the supply voltage, so that the sensor signal swings around Vcc/2.
The simplest way to do this, that came to mind, was to use a voltage divider with 3 resistors between Vcc/Gnd. Two big ones (R1) and a small one in between them (R2). According to this formula, I can pick up a voltage over R2 that is just in the middle between the power rails.
Something like that...
Vcc --- R1 --i-- R2 --i-- R1' --- Gnd
(Found by some simple calcs):
r = R1 / R2
r = ( Vcc - Vdiff ) / ( 2 * Vdiff )
example:
Vcc = 10 V
Vdiff = 1.2 V
r = ( 10 - 1.2 ) / ( 2 * 1.2 ) = 3.66...
So for R1 = 10 k, R2 = 36.6... k
The hall sensor doesn't require much power to work. So thought it should be ok to it that way, and in fact it does work, but isn't really stable somehow... Is this the proper way to do it (I actually don't think it is...)? Is there better still easy way to accomplish that? Maybe with two linear voltage regulators, like the LM317T?
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