Square Wave Generator Circuit with Op Amp IC LM358

Overview

In this tutorial, we will explore the Square Wave Generator Circuit using the Op-Amp IC LM358. The LM358 operational amplifier is versatile enough to be configured for generating a square wave output.

The LM358 IC is a widely used and versatile operational amplifier that finds applications in various circuits including comparators, wave generators, amplifiers, and more.

A square wave generator is an electronic circuit that produces a square wave output. The operational amplifier-based square wave generator is a straightforward circuit that is commonly utilized in function generators. The circuit for the square wave generator is designed using the LM358 op amp.

Bill of Materials

Following are the components required for building this circuit.

Op-Amp IC LM358

The LM358 is a dual operational amplifier IC featuring a wide range of capabilities. This IC is available in several different packages, making it adaptable for various applications. The internal circuitry of the LM358 is designed with numerous transistors to handle diverse analog tasks efficiently.

Notable for its high gain, low power consumption, and ability to operate from a single power supply over a wide range of voltages, the LM358 is particularly suited for battery-operated devices. Additionally, the IC is equipped with short-circuit protection at both the input and output stages, which safeguards the internal components from overload damage. This makes the LM358 a reliable choice for many analog circuits requiring operational robustness.

Check the IC LM358 Datasheets

Square Wave Generator Circuit Diagram using LM358 IC

Take a look at this circuit diagram—it’s a neat setup for a square wave generator using the LM358 operational amplifier, which is configured here as a Schmitt trigger. The core of the circuit includes the LM358 op-amp itself, accompanied by three fixed resistors (R1, R2, and R3), a variable resistor (RV1), and a capacitor (C1).

In terms of layout, there’s a feedback loop in place. The output from the op-amp cycles back to its non-inverting input via R2. This loop is what provides the necessary hysteresis for stable Schmitt trigger operation. The resistors R1 and R2 create a voltage divider that sets critical threshold levels at the non-inverting input—these thresholds help determine when the op-amp switches its output. Meanwhile, the capacitor C1 is linked to the inverting input and plays a vital role in the circuit’s timing, as it charges and discharges according to the settings of the nearby resistors.

This setup not only efficiently churns out square waves via the LM358, but also allows for easy frequency adjustments through the variable resistor RV1.

Working of Square Wave Generator Using Op-Amp 741

The square wave generator circuit using the LM358 op-amp operates based on the principles of a Schmitt trigger, which is a type of comparator circuit with hysteresis.

1. Initial Conditions and Charging:

   When the circuit is powered, the capacitor C1 begins to charge through the resistors R3 and the variable resistor RV1. The initial state of the op-amp’s output (pin 1) is determined by the voltage levels at its non-inverting (pin 3) and inverting (pin 2) inputs. Initially, the non-inverting input, influenced by the voltage divider formed by R1 and R2, is at a lower voltage compared to the inverting input.

2. Reaching the Upper Threshold:

   As C1 charges, the voltage at the inverting input (pin 2) increases. Once this voltage surpasses the voltage at the non-inverting input (pin 3), the output of the op-amp switches from low to high. This switching point is the upper threshold of the Schmitt trigger, which is set by the ratios of R1 and R2.

3. Feedback and Discharging:

   With the output now high, feedback through R2 raises the voltage at the non-inverting input, effectively setting a new, higher threshold for the inverting input to cross back. Meanwhile, the capacitor C1 begins to discharge through R3 and RV1.

4. Reaching the Lower Threshold:

   The voltage at the inverting input decreases as C1 discharges. Once it falls below the elevated threshold at the non-inverting input, the output of the op-amp switches back from high to low. This lower threshold is crucial for the hysteresis characteristic of the Schmitt trigger, preventing noise from triggering false switches.

5. Cycle Repeats:

   After the output switches to low, the feedback through R2 lowers the voltage at the non-inverting input again, setting up the conditions for another cycle of charging and discharging of C1. This cycle repeats continuously, creating a stable square wave at the output.

6. Frequency Adjustment:

   The frequency of the square wave output can be adjusted by varying the resistance of RV1. Increasing RV1 increases the total resistance in the charging and discharging path of C1, which slows down the rate of voltage change at the inverting input, thereby lowering the frequency of the output square wave.

This circuit uses a simple setup where a capacitor charges and discharges through a group of resistors, and the LM358 op-amp acts like a switch that flips between two states. This setup helps produce a steady and clean square wave, which is useful for many electronic applications.

Circuit Simulation

The circuit can be simulated using Proteus Software. The below circuit simulation gives the perfect output on the Oscilloscope. You can change the value of resistors to observe the change in the waveform.

You can also make a Triangular Wave Generator Circuit with Op Amp IC 741 or 741 Based Pulse Generator and in order to view the waveform you can design your own DIY Oscilloscope at home.