“This application note outlines how to implement a single-supply triangle wave oscillator using the MAX9000 and some passive components. This application circuit uses operational amplifiers, comparators and reference voltage sources as active building blocks. The MAX9000 was chosen because it integrates these three components.
This application note outlines how to implement a single-supply triangle wave oscillator using the MAX9000 and some passive components. This application circuit uses operational amplifiers, comparators and reference voltage sources as active building blocks. The MAX9000 was chosen because it integrates these three components.
The linearity of the triangle waveform allows the triangle wave generator to be used in many “sweep frequency” circuits and test equipment. For example, switching power supplies and induction motor control circuits often use triangle wave oscillators as part of a pulse width modulator (PWM) circuit. This article introduces a compact triangle wave oscillator that uses a single MAX9000 IC and some passive components. The MAX9000 series devices integrate high-speed operational amplifiers, high-speed comparators and precision bandgap references.
Figure 1 shows a basic triangle wave generator circuit. ¹It consists of two basic components: an integrator, used to generate a triangular wave output; a comparator, with external hysteresis (Schmitt trigger), the amplitude of the triangular wave can be set as required.
The operational amplifier is configured as an integrator to provide a triangular output. This method is based on the simple fact that the integration of a constant voltage causes a linear ramp. The Schmitt trigger feeds the output of the integrator to its inverting input. The input threshold voltage of the Schmitt trigger is designed to change the state according to the required peak voltage of the triangular wave output.
The circuit in Figure 1 has one drawback: the peak value of the triangle wave can only be symmetrical about the reference voltage applied to the inverting input of the comparator. In order to generate a triangular wave from 0.5V to 4.5V, for example, a reference voltage of (0.5V + 4.5V)/2 = 2.5V is required. Since the output voltage of the standard bandgap reference is 1.23V, it is better to set the voltage range of the triangle wave to a range that has nothing to do with the bandgap reference. This flexibility is achieved by adding resistor R3 in the hysteresis network, as shown in Figure 2, this circuit uses MAX9000. The resistor R3 can set the peak value of the triangle wave independently of the reference voltage.