# voltage divider calculation

Discussion in 'The Projects Forum' started by farkhana, Mar 18, 2012.

1. ### farkhana Thread Starter New Member

Apr 14, 2011
10
0
Hi all,

I need your help everyone..How can I calculate the V5 if I don't know the value of R5..

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2. ### #12 Expert

Nov 30, 2010
16,671
7,314
The answer must be in the form of an equation.

3. ### cybertronics Active Member

Aug 29, 2009
46
0
Go online and google. (Voltage divider).And (voltage divider tutorials).
There's a ton of infromation how to use a voltage divider in a circuit.
They even tell you how to calculate for the input voltage R1 resistor
R2 resistor and output for output voltage.

This will get you started.They also have formula to calculate the divider.

4. ### wmodavis Well-Known Member

Oct 23, 2010
737
150
Just as a rough estimate I would guess it to be approx 1kOhms.

5. ### BillB3857 Senior Member

Feb 28, 2009
2,402
348
The value would also depend upon the resistance to ground that Vout sees. If Vout is left open, it is one extreme. If Vout is connected directly to ground, it is the other extreme.

6. ### wayneh Expert

Sep 9, 2010
12,379
3,232
V5 is ratio R5/(R5+R6) of Vin. Period. Classic exam problem designed to make a student burn precious time if they don't see the concepts.

You DO have to assume Vout impedance is infinite, addressing Bill's point. But with that assumption, the confusing "loop" of resistors just loops around V5, and thus no current flows.

If you can't use the Vout assumption, then you need to express V5 based on Vout, recognizing that R3 and R4 are in parallel with R2, whereas R1 is in series with R2, the result of R1-4 are in parallel to R5, all in series to R6. Messy, but all just logical application of the rules.

Last edited: Mar 19, 2012
7. ### farkhana Thread Starter New Member

Apr 14, 2011
10
0
I have the value for Vin and Vout..
Just want to know how to calculate V5 when R5 is unknown..

I will look up on the internet..