Triangle Wave Generator

Combine a Schmitt trigger and an integrator to generate a triangle and a square wave.

A1 is a Schmitt trigger whose 30 kΩ feedback resistor and 10 kΩ triangle-input resistor set thresholds near ±4 V. A2 integrates its ±12 V square wave through R1 = 30 kΩ and C1 = 100 nF. The 100 MΩ feedback resistor supplies a very weak DC return.

$$\left|\frac{dV_{\mathrm{tri}}}{dt}\right|=\frac{12}{30\,\mathrm{k\Omega}\cdot100\,\mathrm{nF}}=4000\,\mathrm{V/s}$$ $$\begin{aligned}T&\approx\frac{4V_T R_1 C_1}{V_{\mathrm{square}}}=4\,\mathrm{ms}\\f&\approx250\,\mathrm{Hz}\end{aligned}$$

Triangle is green, Square red and triangle-output load current blue. A small capacitor initial condition starts oscillation. The triangle has approximately constant slopes because the integrator sees nearly constant positive or negative voltage.

Read the results. The saved transient chart uses separate voltage and current panels; the table provides numerical samples. The first voltage probe is green and the second red. The first current probe is blue; a second current probe is purple.

Model limits. The three-terminal op-amp model has implicit ±12 V output limits, 200,000 low-frequency gain and 10 MHz gain-bandwidth product. Supply pins are intentionally absent in this functional model. In Schmitt-trigger and relaxation/integrator oscillator examples, the switching amplifier uses a 100 kHz gain-bandwidth setting to resolve transitions cleanly at the saved time step. It omits detailed slew-rate, input common-mode, output-current and thermal limits.

Try it. Set C1 to 200 nF; the triangle frequency approximately halves. Restore the original values after comparing the results.