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Voltage Divider ground change to negative voltage

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mengghee

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can anybody tell me ... what happens if we have a potential divider which the ground is change to a negative voltage and is there any equation that can be used. thank you.
 

This is easily solved from basic information.

1. Calculate the current flowing through the series chain of resistors by dividing the total voltage across the chain by the total resistance. Then calculate the voltage difference across each resistor by multiplying the current times the resistance. Then from knowing the voltage at one end and the drop across each resistor, you can find the voltage at each of the junctions of resistors.
 

    M

    mengghee

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say i have two resistors across them both 2k and 1k. vcc = +15v and vee = -15

current through them is i=v/r

i = 30/3k
= 0.01

so, voltage coming out from one 1k resistor is
v=0.01*1k
=10v
is that right ?

how would we know about the polarity ?

thank you
 

Polarity:

Add voltages starting from the "bottom" ..
For 1kΩ side ..
(-15)+(+10) -->(-5)
or
Deduct voltages starting from the "top" ..
For 2kΩ side:
(+15)-(+20) -->(-5)

Regards,
IanP
 

    M

    mengghee

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actually i am using this kind of potential divider to give a reference voltage to a differential amplifier. i need the reference voltage to be both positive and negative. and i am just wondering, what would the amplifier looks at it as ? whether it is positive and negative because i think measuring an output from a potential divider depends on the gnd. if the op amp is connected to the same negative voltage, what would it see the output of the potential divider as ? thank you


regards,
mengghee

Added after 1 minutes:

IanP,

but my positive and negative voltage is both the same .... ??
 

For an opamp anything above (-Vee) is positive ..
It is YOU who decide whether to call (Vcc-Vee)/2 a 0V(GND) and to connect a voltmeter negative (black) probe to this potential and not to (-Vee) ..

Regards,
IanP
 

    M

    mengghee

    Points: 2
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