# Why is shunt voltage reference not outputting the right voltage?

Thread Starter

#### BrokenPin

Joined Oct 1, 2023
11
Hello,

I have used LM4040C10IDBZR shunt voltage reference to produce 10V from +15V but it is actually outputting 9.4V? this voltage needs to be a stable 10v.
to be honest I don't remember why I chose to put exactly 312ohm in there or if should i put a like voltage divider that makes 10v output and then add the shunt voltage reference in parallel.
what is making the output less than 10v?

Any help would be appreciated.
Thanks

#### Ian0

Joined Aug 7, 2020
9,503
What load is connected to the 10V output?

Thread Starter

#### BrokenPin

Joined Oct 1, 2023
11
What load is connected to the 10V output?
it is going to a voltage divider to make it 5V and then to an opamp input.

#### crutschow

Joined Mar 14, 2008
34,047
it is going to a voltage divider to make it 5V and then to an opamp input.
20 question time.
What is the resistance of the voltage divider?

Thread Starter

#### BrokenPin

Joined Oct 1, 2023
11
20 question time.
What is the resistance of the voltage divider?
in one opamp the divider is composed of two 200k 0.1% resistors and in the other one, it is two 20k 0.1% ones.
each opamp simply form a level shifter.

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#### MrChips

Joined Oct 2, 2009
30,488
Why is the op-amp driving the “voltage divider”?
What is on the left side of the circuit off the picture?

Show us the complete schematic.

#### BobTPH

Joined Jun 5, 2013
8,664
Post the whole exact circuit if you want help.

Thread Starter

#### BrokenPin

Joined Oct 1, 2023
11
Post the whole exact circuit if you want help.
Sorry, I didn't think that would be relevant. here is the full schematic.

#### Attachments

• 331.7 KB Views: 19

#### MrChips

Joined Oct 2, 2009
30,488
Sorry, I didn't think that would be relevant. here is the full schematic.
Famous words here on AAC forums.

#### Ian0

Joined Aug 7, 2020
9,503
Is this a conditioning circuit to measure a 50Hz AC voltage on a microprocessor ADC?

Thread Starter

#### BrokenPin

Joined Oct 1, 2023
11
Is this a conditioning circuit to measure a 50Hz AC voltage on a microprocessor ADC?
it doesn't have to be 50hz but yeah it is to condition a plus/minus 10v bipolar ac voltage to be measured with a 3.3v or 5v mcu.

#### Ian0

Joined Aug 7, 2020
9,503
Try this:
R3=R4=2.R5
R1=R2

R1/R3 = 10/1.65 (for a 10V input and 3.3V supply)
I use MCP60xx op amps.

#### WilkoL

Joined Nov 19, 2023
1
Hello,

I have used LM4040C10IDBZR shunt voltage reference to produce 10V from +15V but it is actually outputting 9.4V? this voltage needs to be a stable 10v.
to be honest I don't remember why I chose to put exactly 312ohm in there or if should i put a like voltage divider that makes 10v output and then add the shunt voltage reference in parallel.
what is making the output less than 10v?
View attachment 307913

Any help would be appreciated.
Thanks
Is R5 really 312 ohm? With 5V over is there would be a current of 16 mA why so much? According to TI max current for the LM4040 is 15 mA.