Manipulating formulas - LM723 Regulator

Thread Starter

Dieverse

Joined Feb 22, 2016
10
Hey there, well as the title states when it comes to manipulation of formulas to solve for a certain variable I have to say, I really am not the best. I absolutely love electronics, and being hands on. But my math could be stronger....

Anyways I need to solve for R1 using the following formula:

Vout = Vref * (R1 + R2) / R2

Vref is given on the data sheet of the Lm723 and I am also supplied with Vout and R2

12V = 7.15V *(R1+10K)/10K

From here I have problems manipulating the formula properly to solve for R1.
Any help is greatly appreciated
 

ericgibbs

Joined Jan 29, 2010
13,267
hi D,
Show us your calculation attempt, we could then see where you are going wrong.
E
Note: Would recommend you use the correct parenthesis [brackets] in the formula's.

I am assuming you are using this formula from the d/s?
A004.gif
 
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Thread Starter

Dieverse

Joined Feb 22, 2016
10
I duno, I think I have it....just need to watch units

12V = 7.15V * (R1+10K)/10K

12V = (715 * 10^-6)(R1) + 7.15

R1 = 12 - 7.15 / (715 * 10^-6)

R1 = 6.78kohm
 

ericgibbs

Joined Jan 29, 2010
13,267
hi D,
Looking good.
What you should do now is to put those values in the formula and see if you get 12V. OK.?
E

EDIT:

Your method works, but it looks a little messy.

Vo = (Vref * (R1 + R2)/R2)

Vo/Vref = (R1 + R2)/R2

R2(Vo/Vref) = R1 + R2

So R1 = R2(Vo/Vref) - R2

Did you check your answer as I suggested.?
 
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Thread Starter

Dieverse

Joined Feb 22, 2016
10
Yes I get 12V, well 11.99...The way I typed it out was more just laziness , I apologize. Its about 5:30am where I am and I have been working on assignments for various classes all night...

The way you laid yours out is how I tried to originally do it, but then would just confuse myself with the second R2

Thank You for your help, really appreciate it.
 
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