This post will show you how to build a special kind of inverter circuit.
It uses two tiny electronic chips IC 555 and IC 4017 to make a smoother version of a square wave inverter.
We will take a close look at all the parts you need and walk you through how to put it together.
Understanding Modified Sine Wave Inverter
There are different types of inverters that can turn battery power into household electricity.
A basic type makes a blocky wave, but a modified sine wave inverter is a step up!
It creates a smoother wave that is better for some appliances.
The key difference is that a modified sine wave inverter holds the voltage at zero for a short bit before switching directions instead of going straight up and down like a switch.
Comparing Square Wave and Modified Sine Wave Inverters
A light switch that can turn on and off really fast.
That is kind of how a square wave inverter works the electricity turns on and off abruptly.
This can be rough on some appliances.
A modified sine wave inverter is smoother, like a dimmer switch.
Instead of going straight on and off, it holds the electricity at zero for a tiny bit before switching directions.
This makes the electricity cleaner and less likely to cause problems with your devices.
While it is not perfect it cannot be as smooth as a true sine wave, it is a big improvement over the square wave.
Understanding the Modified Inverter Circuit
Components List:
| Component | Quantity |
|---|---|
| Resistors (all 1/4 W CFR) | |
| 36k | 2 |
| Capacitors | |
| PPC 0.1µF | 2 |
| Electrolytic 1000µF / 25V | 1 |
| Semiconductors | |
| Diode 1N4007 | 1 |
| IC 4017 | 1 |
| IC 555 | 1 |
| MOSFET IRF540 | 2 |
| Other Components | |
| Transformer 6-0-6V / 25A / 220V | 1 |
| Battery 12V 25Ah | 1 |
The modified inverter circuit produces a modified sine wave at its output, and it can be broken down into the following stages:
Oscillator Stage IC 555
The oscillator circuit plays a pivotal role in generating the required clock signal for the inverter, making it the heart of the entire system.
To achieve this, we utilize the versatile IC 555 as the oscillator.
Our objective is to produce a 200Hz square wave with a 50% duty cycle, which will be further divided by four using IC 4017 to obtain a 50Hz AC modified sine wave output.
The frequency of the IC 555 oscillator can be calculated using the following formula:
Formulas and Calculations:
Frequency = 1.44 / (R1 + R2) * C
Duty Cycle = R1 / (R1 + R2)
By substituting the component values from the circuit diagram into these formulas, we can calculate:
Frequency = 1.44 / (36000 + 36000) * 0.1 x 10-6 = 200 Hz
Duty Cycle = 36000 / (36000 + 36000) = 0.5
Duty Cycle = 0.5 x 100% = 50%
Let us analyze this on the scope:
The scope measurements confirm that the circuit aligns closely with these calculated values, with minor discrepancies attributed to component tolerances.
Important Note:
It is crucial not to omit the 0.1uF capacitor at pin 5 of IC 555, as it provides stability against external noise.
Omitting this capacitor will alter the frequency and duty cycle from the calculated values.
Wave Shaping Stage IC 4017
In the wave shaping stage, we feed the 50Hz, 50% duty cycle signal to the IC 4017, a decade counter that produces the modified sine wave.
The IC 4017 boasts 10 output pins and one input pin (pin 14).
When a clock signal is applied to the input pin, each of the 10 output pins becomes active sequentially.
For instance, applying 5 clock pulses activates the 5th output, while the rest of the pins remain inactive.
Pin #15 can be used to reset the count back to zero if all 10 outputs are not required.
In our case, we utilize only 4 output pins: pin 3, 2, 4, and 7 (outputs Q0, Q1, Q2, Q3).
Pin 15 is connected to output pin Q4 or pin 10, causing the output pins 3, 2, 4 and 7 to remain active while the other 6 output pins stay inactive.
With the 200Hz signal fed into the clock pin of IC 4017, we only connect two alternate outputs: Q0/pin 3 and Q2/pin 4.
The remaining pins are left unconnected.
By observing the waveform on pins 3 and 4 using an oscilloscope, we obtain the modified sine wave, which will be further amplified by MOSFETs in the subsequent stages of the circuit construction.
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