The post explains how an ordinary IC 555 astable multivibrator could be used to make an inverter without involving complex stages. WE will discuss 5 intresting IC 555 based designs, each having its own unique features and specifications.

The idea was requested by Mr. ningrat_edan.



Referring to the shown diagram, a single IC 555 can be seen configured in its standard astable mode, wherein its pin#3 is used as the oscillator source for implementing the inverter function.



1) Using IC 555 as the Astable Oscillator


In an astable mode the pin#3 of IC 555 generates an alternating high/low pulses at a particular frequency rate depending on the values of the resistors and capacitor across its pin#7, Pin#6, 2 etc.

As per the diagram this pin#3 oscillating is fed to a couple of BC547/BC557 buffer driver stages, where one of the stages receives an oppositely oscillating frequency due to the inclusion of an extra BC547 inverter stage.

This ensures that when the left side BC547/BC557 responds to a positive pulse from pin#3 of the IC, the other BC547/BC557 stage is inhibited from the pulse, and their bases are grounded with the aid of the intermediate BC547 conduction.

The above flip-flop functioning of the two BJT stages in turn allow the attached power mosfets to conduct alternately and activate the associated transformer winding with a push-pull current from the battery.

The response allows the transformer to generate the required AC across its secondary winding and implement the intended IC 555 inverter circuit functioning.

The zener diodes at the gates of the mosfets introduce a slight delay time or dead time between the mosfet conduction and inhibits any possibility of both mosfets getting engaged together even for a fraction of a second.

Simplified Version for the above IC 555 Inverter Design


The above shown design can be actually made simpler by removing the BC547/BC557 buffer stages as shown below:


Technical Specifications:


Power Output: Unlimited, can be between 100 watt to 5000 watts

Transformer: As per preference, Wattage will be as per the Output Load wattage requirement

Battery: 12V, and Ah rating should be 10 times more than the current selected for the transformer.

Waveform: Square Wave

Frequency: 50 Hz, or 60 Hz as per country code.

Output Voltage: 220V or 120V as per country code

Video Clip:




Waveform Image:


2) IC 555 Full Bridge Inverter Circuit

The idea presented belowcan be considered as the simplest IC 555 based full bridge inverter circuit which is not only simple and cheap to build but is also significantly powerful. The power of the inverter may be increased to any reasonable limits y suitably modifying the number of mosfets at the output stage.

How it Works


The circuit of a simplest full bridge power inverter explained requires a single IC 555, a couple of the mosfets and a power transformer as the top ingredients.

As shown in the figure, the IC 555 has been wired as usual in the an astable multivibrator form. The resistors R1 and R2 decides the duty cycle of the inverter.

R1 and R2 must be adjusted and calculated precisely for getting a 50% duty cycle, otherwise the inverter output may generate unequal waveform, which may lead to unbalanced AC output, dangerous for the appliances and also the mosfets will tend to dissipate unevenly giving rise to multiple issues in the circuit.

The value of the C1 must be chosen such that the output frequency comes to about 50 Hz for 220V specs and 60 Hz for 120V specs.

The mosfets can be any power mosfets, capable of handling huge currents, may be upto 10 amps or more.

Here since the operation is a full bridge type without any full bridge driver ICs, two batteries are incorporated instead of one for supplying the ground potential for the transformer and in order to make the transformer secondary winding responsive to both positive and negative cycles from the mosfet operations.

The idea has been designed by me, however it has not been yet tested practically so kindly take this issue into consideration while making it.

Assumably the inverter should be able to handle upto 200 watts of power easily with great efficiency.

The output will be a square wave type.


Parts List


R1 and R2 = See Text,
C1 = See text,
C2 = 0.01uF
R3 = 470 Ohms, 1 watt,
R4, R5 = 100 Ohms,
D1, D2 = 1N4148
Mosfets = see text.
Z1 = 5.1V 1 watt zener diode.
Transformer = Asper power requirement,
B1, B2 = two 12 volts batteries, AH will be as per preference.
IC = 555

3) Using IC 555 and IC 4017


In this inverter design we use a 4017 decade counter and a ne555 timer Ic to generate a sinewave pwm signal for the inverter and an Arduino based automatic high/low battery cut-off with alarm.

By: Ainsworth Lynch

Introduction

In this circuit what actually happens is that the 4017 outputs a pwm signal from 2 of its 4 output pins which is then chopped up and if the proper output filtering is in place at the secondary side of the transformer it takes the shape or close enough to the shape of an actual sine wave form.

The first NE555 feeds a signal to pin 14 of the 4017 which is 4 times the required output frequency that you need since the 4017 switches across its 4 outputs, in other words if you need 60hz you would need to supply 4*60hz to pin 14 of the 4017 IC which is 240hz.

This circuit has an over voltage shutdown feature, under voltage shutdown feature and a low battery alarm feature all that is done by a microcontroller platform called the Arduino which needs to be programmed.

The program for the Arduino is straight forward and has been provided at the end of the article.

If you feel that you won’t be able to complete this project with the micro controller added it can be omitted and the circuit will work just the same.

How the Circuits Works

This IC 555 Inverter with Arduino Hi/Low Battery Shutdown Circuit can work from 12v, 24, and 48v going to 48v an appropriate version voltage regulator would have to be selected and the transformer sized accordingly also.

The Arduino can be powered with 7 to 12v or even 5v from a usb but for a circuit like this it would be good to power it from 12v as not to have any voltage drop on the digital output pins which is used to power a relay which turns on the Ic in the circuit and also a buzzer for low voltage alarm.

The Arduino will be used to read battery voltages and it only works from 5V DC so a voltage divider circuit is used I used a 100k and a 10k in my design and those values are plotted in the code that is programmed in the Arduino chip so you have to use the same values unless you made modification to the code or write a different code which can be done since the Arduino is an open source plat form and its cheap.

The Arduino board in this design is also connected up with an LCD display 16*2 to display battery voltage.



Below is the schematic for the circuit.




I also designed the PCB for this specific SG3525 inverter with Arduino battery charger circuit, you can check it out and download it if needed from this link

Program for the Battery Cut Off:


#include <LiquidCrystal.h>
LiquidCrystal lcd(7, 8, 9, 10, 11, 12);
int analogInput = 0;
float vout = 0.0;
float vin = 0.0;
float R1 = 100000.0; // resistance of R1 (100K) -see text!
float R2 = 10000.0; // resistance of R2 (10K) - see text!
int value = 0;
int battery = 8; // pin controlling relay
int buzzer =7;
void setup(){
pinMode(analogInput, INPUT);
pinMode(battery, OUTPUT);
pinMode(buzzer, OUTPUT);
lcd.begin(16, 2);
lcd.print("Battery Voltage");
}
void loop(){
// read the value at analog input
value = analogRead(analogInput);
vout = (value * 5.0) / 1024.0; // see text
vin = vout / (R2/(R1+R2));
if (vin<0.09){
vin=0.0;//statement to quash undesired reading !
}
if (vin<10.6) {
digitalWrite(battery, LOW);
}
else {
digitalWrite(battery, HIGH);
}
if (vin>14.4) {
digitalWrite(battery, LOW);
}
else {
digitalWrite(battery, HIGH);
}
if (vin<10.9)) {
digitalWrite(buzzer, HIGH)
else {
digitalWrite(buzzer, LOW
lcd.setCursor(0, 1);
lcd.print("INPUT V= ");
lcd.print(vin);
delay(500);
}

Sine Pulse Width or SPWM IC 555 Inverter Circuit

SPWM waveform stands for sinewave pulse width modulation waveform and this is applied in the discussed SPWM inverter circuit using a few 555 ICs and a single opamp.

In one of my earlier posts we elaborately learned how to build a SPWM generator circuit using an opamp and two triangle wave inputs, in this post we use the same concept to generate the SPWMs and also learn the method of applying it within a IC 555 based inverter circuit.



4) Using IC 555 for the Inverter


The diagram above shows the entire design of the proposed SPWM inverter circuit using IC 555, where the center IC 555 and the associated BJT/mosfet stages forms a basic square wave inverter circuit.

Our aim is to chop these 50Hz square waves into the required SPWM waveform using an opamp based circuit.

Therefore we accordingly configure a simple opamp comparator stage using the IC 741, as shown in the lower section of the diagram.

As already discussed in our past SPWM article, this opamp needs a couple of triangle wave sources across its two inputs in the form of a fast triangle wave on its pin#3 (non-inverting input) and a much slower triangle wave at its pin#2 (inverting input).

IC 555 Pinouts


Using IC 741 for the SPWM


We achieve the above by using another IC 555 astable circuit which can be witnessed at the extreme left of the diagram, and use it for creating the required fast triangle waves, which is then applied to the pin#3 of the IC 741.

For the slow triangle waves we simple extract the same from the center IC 555 which is set at 50% duty cycle and its timing capacitor C is tweaked appropriately for getting a 50Hz frequency on its pin#3.

Deriving the slow triangle waves from the 50Hz/50% source ensures that the chopping of the SPWMs across the buffer BJTs is perfectly synchronized with the mosfet conduct ions, and this in turn ensures that the each of the square waves are perfectly "carved" as per the generated SPWM from the opamp output.

The above description clearly explains how to make a simple SPWM inverter circuit using IC 555 and IC 741, if you have any related queries please feel free to use the below given comment box for prompt replies.

Update:

A deeper investigation reveals that the slow triangle waves must have  a frequency of 100Hz and not 50 Hz for creating correctly dimensioned SPWMs, this may be done by using a frequency doubler stage bewtween pin#2 of the IC 741 and the 50Hz from pin#6/2 of the center 555 IC.

5) Designing a Compact Ferrite Core IC 555 Inverter


The above concept is based on an iron core transformer, in order to convert it into a compact ferrite cored IC 555 inverter circuit, the iron transformer could be replaced with a ferrite EE core transformer consisting of 9 + 9 turns for the primary, and 300 turns for the secondary, using 0.8mm wire for the primary and 0.3 mm wire for the secondary.

This will also need the 555 frequency to be increased to around 50kHz, instead of the 50Hz assigned for the orin core transformer.

IC IRS2453 Pinouts


For a Ferrite Core Compact Version


Also, for implementing a ferrite core inverter, the output from the transformer will need to be rectified using a bridge rectifier and the resulting DC fed to a 50Hz full bridge or H-bridge processor, as shown below:



In this processor circuit the IC 555 functions as an adjustable PWM generator while IRS2453 constitutes the full bridge driver circuit, together the stages execute a pure sine sine wave waveform for the proposed IC 555 inverter circuit.

For more info you may feel free to express your queries through comments.

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