The post explains how an ordinary IC 555 astable multivibrator could be used to make an inverter without involving complex stages.
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.
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:
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
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.
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
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.
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.
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.
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 555 Pinout
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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