LM331 Based Frequency to Voltage Converter Circuit

Simple F/V converter is cool circuit.

It changes signal with different frequency to DC voltage same as that frequency.

It is used in many things like tachometer, speedometer and factory machines.

LM331 is popular IC for this and it can do both V/F and F/V.

It is very accurate and very flexible.

Here LM331 works as F/V converter and it change input frequency to voltage.

Voltage goes up when frequency goes up.

Circuit uses 15V DC power.

This article for LM331 Based Frequency to Voltage Converter Circuit show how F/V converter works using LM331 IC.

It give formulas and steps to make circuit.

Circuit Working:

Parts List:

This article show circuit that change frequency to voltage using LM331 IC.

Main parts of this circuit are resistors, capacitors and LM331 chip.

LM331 take frequency signal and give voltage output.

Conversion happen by using capacitor C3 and resistor R6 and they make pulse signal go to pin 6 of IC.

Resistor R3 keep circuit stable and give right bias and resistor R5 and preset VR1 set reference voltage.

And this change output voltage level.

When frequency signal come then IC LM331 make pulses.

Pulse duty cycle change with frequency.

Pulses go through capacitor C2 and resistor R4 to become smooth DC voltage and this voltage match input frequency

Formulas:

To make simple LM331 F/V converter we need to use these formulas:

Output voltage (Vout) and input frequency (Fin) is link by:

Vout = K × Fin

where:

• K is scale factor and it depends on R4, C2 and IC setup.
• Fin is input frequency in Hz.

To find Vout using ICs charge pump the formula is:

Vout = Iavg × R4

Iavg = (Vref / R5) × T

where:

• T is pulse time and it depends on frequency.
• Vref is IC LM331s inside reference voltage.

How to Build:

To build a LM331 Based Frequency to Voltage Converter Circuit follow the below mentioned steps for connections:

• Gather all parts shown in diagram.
• Pin 1 of LM331 connect to output line using R4 and C2 and then to GND.
• Pin 2 connect to GND with R5 and VR1 preset.
• Pin 3 and Pin 4 connect to GND.
• Pin 5 connect to GND using capacitor C1.
• One side of R1 go to +15V and other side to pin 5.
• Pin 6 connect to input frequency Fin using C3.
• One side of R6 go to +15V and other side to pin 6.
• Pin 7 connect to GND with resistor R3.
• R2 connect from +15V to pin 7.
• Pin 8 connect to +15V.

Conclusion:

Simple LM331 Based Frequency to Voltage Converter Circuit is easy and works well.

It is good for speed sensors, tachometers and industrial systems.

Change R4 and C2 to adjust output voltage.

Understand circuit and use formulas to make it fit different frequency and voltage needs.

References:

Precision voltage-to-frequency converter with 1-Hz to 100-kHz full scale frequency