Frequency to Voltage Converter Using LM331
Category: Miscellaneous
Designer: RANA MUHAMMAD ADNAN KHALIL
Notes
This circuit is designed and simulated in proteus 7.10. In this circuit you will learn how frequency is converted to voltage signal. 1. The IC used for frequency to voltage (f to v) is LM331. 2. This IC can work in bidirectional mode, that is frequency to voltage (f to v) conversion and voltage to frequency (v to f) conversion. 3. In this circuit it is used in f to v mode, the v to f mode is explained in previous circuits. Therefore to understand v to f, go to previous circuits. 4. The input frequency is given at pin 6 through capacitor (C3 = 470pF). 5. The pin 6 is also pull up to VCC (+15VDC) via resistor R6 (10k). 6. The output is taken at pin 1 in the form of current and this current flows through fix resistor R4. 7. The output voltage is generated across resistor R4 (V=I*R). 8. The gain can be adjusted by changing resistor R4 or capacitor C4. 9. The gain can also be adjusted by varying resistor RV1. 10. The current pump circuit forces the voltage at pin 2 to be at 1.9 V, and causes a current i = 1.90 V/Rs to flow. 11. When Rs (RV1 + R5) is 14k ohm, the output current Iout is 135uA. 12. This current can be vary from 10uA to 500uA by varying Rs. This current is pulsating. 13. The average current flowing out of pin 1 is Iavg = i * (1.1Rt*Ct) * f 14. This current is converted to voltage via fix resistor R4 (Vo = Iavg*R4) 15. The output voltage can also be calculated using this equation Vout = Fin*2.09V*(RL/Rs)*(Rt*Ct) where RL is R4 Applications: 1. This circuit can be used as tachometer. 2. This circuit can also be used to measure the frequency. Note: More circuits are coming soon. If you want any circuit then feel free to contact. (The five star rating is highly appreciated. Thanks)