# Series-pass voltage regulator

Discussion in 'Homework Help' started by notoriusjt2, Dec 15, 2010.

Feb 4, 2010
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2. ### t_n_k AAC Fanatic!

Mar 6, 2009
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The key elements are the zener diode voltage and the values of R2 & R3.

R2 & R3 form a voltage divider across the output. The LM741 op-amp will attempt to control the output such that the R2 + R3 divider output voltage fed back to the LM741 negative input is the same as the zener voltage.

3. ### notoriusjt2 Thread Starter Member

Feb 4, 2010
209
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ahhhh i see

Vout/Vin = R3/(R2+R3)
Vin=10V

Last edited: Dec 16, 2010
4. ### Ron H AAC Fanatic!

Apr 14, 2005
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That makes no sense when looking at your schematic.

5. ### notoriusjt2 Thread Starter Member

Feb 4, 2010
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sorry i was reading that formula off my paper where I had it translated for R1 and R2

it should be
Vout/Vin = R3/(R2+R3)

6. ### Ron H AAC Fanatic!

Apr 14, 2005
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You came up with Vin=10V. Which node is Vin?

7. ### notoriusjt2 Thread Starter Member

Feb 4, 2010
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i guess you could call it the top of R2.

between R2 and R3 is 5.6V

the bottom of R3 is GND

is this not correct?

8. ### Ron H AAC Fanatic!

Apr 14, 2005
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I think you have figured it out. I just thought it would make more sense if you called the junction of R2 and R3 Vin, and the top of R2 Vout, since that's how it's labeled on the schematic.
If you do that, Vout/Vin=(R2+R3)/R3.
If you want to communicate using schematics, it is helpful if you stick to the labeling and reference designators on the schematic.