The relaxation circuit shown in figure 1 using an operational amplifier can produce signals from very low frequencies (under 1 Hz) up to 100 kHz according the used Op. Amp. The output is a square wave but in the junction between R and C the signal is sawtooth wave.
Formula 1
Square Wave Oscillator:
f = 1 / (6 x R x C)
Where:
f is the frequency in hertz (Hz)
R is the resistance in ohm (Ω)
C is the capacitance in farads (F)
Application example:
Determine C to a frequency of 10 kHz given R = 10 kΩ. The circuit is shown in figure 2.
Figure 2 – The circuit
Data:
f = 10 kHz
R = 10 kΩ
C = ?
Using formula 1:
10 x 103 = 1 / (6 x 10 x 103 x C)
Isolating C:
C = 1 / (6 x 10 x 103 x 10 x 103)
C = 1 / (600 x 106)
C = (1 / 600) x 10-6
C = 0.0016 µF
C = 1.6 nF
