Making a Pure Sine Wave Inverter – Concept Explored

Through a simple concept, the idea of building a pure sine wave inverter has been explained in the article. Read on to know the whole construction details.

A pure sine wave inverter or rather a sine wave inverter circuit is hard to find and the available ones are too complicated for everyone to understand. A simple concept through circuit schematic has been explained here.

A Viable Concept

It’s true that sine wave inverters are not easy to build, due to many different reasons. But it’s probably the most sort after circuit and also pretty difficult to find. For the folks who are desperately looking for such a circuit, perhaps this article can help.

After a lot of thinking, I probably seem to have designed an easier (though not quite efficient) concept of a pure sine wave inverter circuit. Since the circuit has not been tested by me so won’t be able to tell much regarding the exact specifications of the circuit and would like to leave it up to the readers to decide the feasibility of the present circuit.

The idea struck me while reading the circuit description of a MOSFET audio amplifier. We all know that when an audio signal is fed at the input of an amplifier, it produces an amplified output power having exactly the same properties as the input.

That simply implies, in place of an audio signal if a pure AC signal say from a Wien bridge circuit is applied to the input of a power amplifier and an inverter transformer connected to its output (where normally a speaker would be connected), it would certainly produce an amplified replica of the input. And the secondary winding of the connected inverter transformer would definitely produce a sine wave AC power (My assumption).

The only big problem is the loss of a significant amount of battery power in the form of heat through the power devices reducing the overall efficiency of the inverter.

Let’s move on and see how the different stages of the proposed circuitt functions.

The Oscillator Circuit

The simple sine wave generator circuit shown alongside may be used to produce the required sine waves at the input of the power amplifier, let’s study regarding its functioning through the following steps:

Op amp A1 is basically wired as an astable multivibrator,

Resistor R1 and the capacitor C1 define the frequency of oscillation of the astable.

The square wave from A1 is fed to A2 which is configured as a double pole low pass filter and is used to filter out the harmonics from A1.

The output from A2 will be almost a pure sine wave, the peak will obviously be dependent on the supply voltage and on the type of the op amp used.

The frequency of the present circuit has been fixed to approximately 50 Hz. If the values of parts shown in the parenthesis are selected, the frequency will be around 60 Hz.

Parts List

All resistors are 1/8 watts, 1%, MFR

R1 = 14K3 (12K1),

R2, R3, R4, R7, R8 = 1K,

R5, R6 = 2K2 (1K9),

R9 = 20K

C1, C2 = 1µF, TANT.


C4, C6, C7 = 2µ2/25V,

C5 = 100µ/50v,

C8 = 22µF/25V

A1, A2 = TL 072

IC2 = LM3886 (National Semiconductor),


TRANSFORMER = 0 – 24 V/8 AMPS. OUTPUT – 120/230 V AC


The Power Amplifier Circuit

In view of keeping the design specifications very simple, and the component count as minimum as possible, a single chip amplifier was the basic requirement. A reasonably powerful amplifier using IC LM3886 (National Semiconductor) was ultimately selected by me for the purpose. The salient features of this power amplifier chip are as follows:

Truly versatile and a high performance IC compared to the other types of hybrid and discrete devices.

Totally internally protected from instantaneous peak temperatures,

Has got a dynamically protected safe area of operation,

The out put is perfectly shielded against a short circuit with the ground or the positive supply through an internal current limiting circuit network.

The output is also protected against output over voltages due to inductive load transients,

Can be operated with voltages as low as 20 volts up to a staggering 94 volts.

Its technical specifications are as follows:

Input sensitivity is 1 Vrms

Output power will be in the vicinity of 100 watts if the transformer primary resistance is around 4 Ohms.

Power bandwidth is a massive 10 Hz to 100 KHz.

Construction Hints

The circuit basically consists of just two ICs as the main active components and a handful of other passive components, so the construction procedure should be very easy. The whole assembly may be simply done over a piece of general purpose board (approximately 4 by 4 inches).

IC2 should be positioned at the edge of the PCB to facilitate easy fitting of the heat sink. The present utilizes two large 24 volt truck batteries. Connect them as shown in the diagram.

A separate battery charger is required to charge the batteries.