LM331 Frequency to Voltage Conveter Problem

Hidetoshi Matsunami

Expert 2750 points

Other Parts Discussed in Thread: LM331

Hello,

I have one question under the following conditions.

The output voltage was saturated at 3.8V when Fin change from 4.8kHz to more than 6.2kHz.

Could you tell me any solutions?

Best Regards,

Hidetoshi Matsunami

over 12 years ago

0 Michael Stout over 12 years ago

TI__Genius 16890 points

Hello,

The formula for this schematic is located below the schematic. You can try decreasing the value of RL or increase the value of RS to lower the value of Vout.

Mike

0 Hidetoshi Matsunami over 12 years ago in reply to Michael Stout

Expert 2750 points

Hello, Mike.

I had expected Vout increase to about 4.67V at Fin=7kHz.

But Vout can increase up to 3.8V under the following conditions.

- Vs=5V

- RL=68kΩ

- Rs=12.5kΩ

Could you tell me the conceivable causes for that?

Fig.1 The schematics from data sheet

Fig.2 After change the conditions

Best regards,

Hidetoshi Matsunami

0 Michael Stout over 12 years ago in reply to Hidetoshi Matsunami

TI__Genius 16890 points

Hello,

Looking at the schematic diagram of the LM331 in the datasheet, this part is not a rail to rail output. I think you are running into the output limit which appears to be two diode drops below the 5V supply.

Try increasing the supply to 10V and see if you get the correct value.

Mike

0 Hidetoshi Matsunami over 12 years ago in reply to Michael Stout

Expert 2750 points

Hi Michael,

I am grateful for your polite response.

Let me make a reference.

Thank you very much.

Best Regards,

Hidetoshi Matsunam

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LM331 Frequency to Voltage Conveter Problem