Demonstrating the LM2907 Frequency to Voltage Converter for Hobbyist Electronics
In this video we will take a look the LM2907 Frequency to Voltage Converter integrated circuit. This will be an on the bench demonstration using the datasheet test circuit with minimal components. Using a Function Generator to provide the source frequency we will monitor using an Oscilloscope the voltage versus frequency and examine the response to a Sweep signal at various rates.
Minimal Component Diagram
The following resistor and capacitor values can be changed to affect voltage and frequency range (extract from LM2907 datasheet)
C1: This capacitor is charged and discharged every cycle by a 180-µA typical current source. Smaller
capacitors can be charged quicker therefore increasing the maximum readable frequency. However, lower
capacitors values reduce the output voltage produced for a given frequency. C1 must not be sized lower than
500-pF die to its role in internal compensation.
R1: This resistor produces the output voltage from current pulses source by the internal charge pump. Higher
values increase the output voltage for a given frequency, but too large will degrade the output’s linearity.
Because the current pulses are a fixed magnitude of 180 µA typical, R1 must be big enough to produce the
maximum desired output voltage at maximum input frequency. At maximum input frequency the pulse train
duty cycle is 100%, therefore the average current is 180 µA and R1 = Vo(max) / 180 µA.
C2: This capacitor filters the ripple produced by the current pulses sourced by the charge pump. Large values
reduce the output voltage ripple but increase the output’s response time to changes in input frequency.
LM567 Tone Decoder