How to Build a Simplest Modified Sine Wave Power Inverter Circuit

Here we discuss a circuit design of a modified sine wave power inverter unit that’s probably the simplest and the cheapest to build. Whole circuit description and circuit schematic is included here in, read on.....

Circuit Design Discussion

In one of my recent articles I discussed a circuit design of a modified sine wave power inverter and we came to know how it’s different and more efficient than a few other designs available in some other websites. In this article we go through yet another design of a modified sine wave inverter which may not be as efficient as the previous one but is definitely better than a square wave design and is also perhaps the simplest one to build.

Folks who are new to electronics may get a bit confused regarding the difference between a square wave and a modified square wave inverter. It may be understood through the following brief explanation:

As we all know an inverter will always generate an alternating current (AC) similar to our domestic AC line voltage so that it can replace it during power failures. An AC in simple words is basically a rise and fall of voltage of a particular magnitude.

This rise and fall of voltage happens at a particular rate i.e. at a particular number of times per second, known as its frequency. So for example a 50 Hz AC means 50 cycles or 50 ups and downs of a particular voltage in one second.

In a sine wave AC as found in our normal domestic mains outlet the above rise and fall of voltage is in the form of a sinusoidal curve, i.e. its pattern gradually varies with time and thus is not sudden or abrupt. Such smooth transitions in the AC waveform becomes very suitable and a recommended type of supply for the many common electronic gadgets like TVs , music systems , Refrigerators, motors etc.

However, in a square wave pattern the voltage ups and downs are instant and sudden. Such immediate rise and fall of potential creates sharp spikes at the edges of each wave and thus becomes very undesirable and unsuitable for sophisticated electronic equipments. Therefore it is always dangerous to operate them through a Square weave inverter supply.

In a modified square wave design, the waveform shape basically remains the same but the size of each section of the wave-form is appropriately dimensioned so that its average value matches closely to an AC waveform’s average value.

For the present design we yet again take the help of the evergreen versatile IC 4017.

We know that when a clock input is applied to its pin #14, the IC produces a shifting cycle logic high pulses through its 10 output pins.

Looking at the circuit diagram we find that the pin outs of the IC are terminated to supply the base of the output transistors such that they conduct after every alternate output pulse from the IC.

This happens simply because the bases of the transistors are connected alternately to the IC pin outs and the intermediate pin-out connections are just eliminated or kept open.

The transformer windings which are connected to the transistor’s collector respond to the alternate transistor switching and produce a stepped up AC at its output having a waveform exactly as shown in the diagram.

The output of this Modified sine wave power inverter is although not quite comparable to the output of a pure sine wave inverter but definitely will be far better than that of an ordinary square wave inverter. Moreover the idea is very easy and cheap to build.

 

QUIZ = Can anybody tell the reason behind powering IC2 via T0 and the associated circuit instead of providing a direct supply to its pin 16?


Parts List

R1=20K

R2,R3=1K
R4,R5=220 Ohms, 1 watt
C1=0.095Uf

C2,C3,C4=10UF/25V

T0 = BC557B

T1,T2=TIP122

T3,T4=BDY29

IC1= SN74LVC1G132 or a single gate from IC4093

IC2=4017

IC3=7805

TRANSFORMER=12-0-12V/10AMP/230V