example of a relaxation oscillator(The op-amp triangular-wave generator)

The op-amp triangular-wave generator is another example of a relaxation oscillator. We know that the integrator output waveform will be triangular if the input to it is a square-wave. It means that a triangular-wave generator can be formed by simply cascading an integrator and a square-wave generator, as illustrated in figure. This circuit needs a dual op-amp, two capacitors, and at least five resistors. The rectangular-wave output of the square-wave generator drives the integrator which produces a triangular output waveform. The rectangular-wave swings between +V_sat and -V_sat with a time period determined from equation. The triangular-waveform has the same period and frequency as the square-waveform. Peak to-peak value of output triangular-waveform can be obtained from the following equation.

The input of integrator A₂ is a square wave and its output is a triangular waveform, the output of integrator will be triangular wave only when R₄ C₂ > T/ 2 where T is the ( period of square wave. As a general rule, R₄C₂ should be equal to T. It may also be necessary to shunt the capacitor C₂ with resistance R₅ = 10 R₄ and connect an offset volt compensating network at the non-inverting (+) input terminal of op-amp A₂ so as to obtain a stable triangular wave. Since the frequency of the triangular-wave generator like any other oscillator, is limited by the op-amp slew-rate, a high slew rate op-amp, like LM 301, should be used for the generation of relatively higher frequency waveforms.

S:circuitstoday.com