555 sine wave inverter schematic

[tcmtech]

Some time ago I tackled the concept of how to build a complete and functioning yet simple all analog based Grid Tie Inverter, GTI, that could be built out of common parts and salvaged components so to further expand on the theme of low price recycle AE tech I came up with a fairly simple and strait forward design for a full PWM sine wave power inverter that can also be built out of second hand parts and pieces with little more than two 555 timers, a LM1458 op amp, and a IRF2110 IGBT/Mosfet driver IC.

The point and purpose of this design is to put a defined answer to that never ending question that every electronics forum sees almost every single day which we all know as, 'Please sirs I have need for 555 sine wave inverter circuit' or something to that effect. So to answer that never ending question here is a complete yet basic 555 timer IC based pulse width shaped sine wave power inverter schematic that is adaptable to almost any range of input and output voltages and power levels while still being buildable from basic common parts.

The basic principal behind this design is that the common 555 timer IC can operate in a number of different modes with only a few additional resistors and capacitors in order to serve in a wide range of functions and applications. In this circuit the two 555 timer IC’s are working together to produce two base frequency wave forms which are added together in the LM1458 Op amp IC resulting a 50 or 60 Hz PWM shaped sine wave superimposed on a 30KHz base switching frequency.

In order to produce a high frequency PWM signal that can be widely varied from 0 to 100% duty cycle with a 50 or 60 Hz sine wave superimposed on it the U1 555 timer IC set up to produce a constant 50% duty cycle 30 KHz square wave. That 50% duty cycle square wave gets passed through a simple RC filter that reshapes it into a symmetrical triangle wave. From there that signal is then fed to the negative input of U3b which is set up in a standard comparator configuration where the 30 KHZ signal is used to create a steady 30 KHz square wave that can now be fully modulated from 0 to 100% duty cycle by varying the voltage on the positive input of the comparator.

To produce the 50 or 60 Hz sine wave with the U2 555 timer IC the normal square wave output is reshaped into an approximated sine wave by passing it through a pair of simple RC low pass filters. In the first filter stage it gets reshaped from the square wave to a symmetrical triangle wave where it then can be passed onto the second stage that further reshapes the triangle wave into the approximated sine wave which is what gets fed to the positive input pin of the LM1458 U3a IC. The LM1458 U3a op amp is working as part of a voltage feedback loop that varies and stabilizes the gain of the system so that a basic but fairly effective automatic voltage regulation can be performed.

By combining the two different signals in the LM1458 U3b two fixed duty cycle signals are able to be turned into a PWM shaped sine wave that is based on the 30 KHZ a carrier frequency and the superimposed 50 or 60 Hz sine wave approximation.


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[tcmtech]

THEORY OF OPERATION​

555 Timer IC’s.

In this application both 555 timer IC’s are configured in a unique way using the pin 3 output to control the charge and discharge of the timing capacitors through a single resistor making for a very simple and effective way to get a 50% duty cycle output with minimal parts.

If this circuit configuration on an ideal or theoretically perfect 555 IC the output would be exactly 50/50 duty cycle but unfortunately in reality due the slight variances in the internal design that happen during the manufacturing process there can be a slight duty cycle offset that can favor one direction or the other much as 15% from the expected 50/50 duty cycle. In order to compensate for this effect a slight counter biasing of the control input is necessary by connecting 1K potentiometers to the pin 5 control inputs to externally re bias the control voltages and correct that natural offset issue.


LM1458 Dual op amp IC.

The dual op amp LM1458 IC is serving two functions in this circuit part U3a is working as a output voltage sensing feedback control to keep the output voltage stable regardless of the load variations and or input voltage variations. Due to the high 30KHz carrier frequency of the PWM system the power transformer does not carry that over into the output to any great degree being it is many times higher than the designed 50 - 60 Hz working range that typical iron core power transformers are designed to work with. Because of this high frequency damping and filtering effect the output can be fed back to the U3a negative input through a simple two resistor voltage divider network. What this does is create a sort of voltage follower or amplifier feedback loop that tries to keep the output voltage and wave form the same as what is being fed into the U3a positive input pin while ignoring the underlying 30 KHz PWM signal be generated by U3b.


IRF2110 half bridge driver IC.

The IRF2110 half bridge driver IC is used in order to produce a very fast and efficient turn on and turn off time of the two power switching devices. In this configuration the output that is normally capable of being used for a high side driver is set up identical to the low side driver since it is working as a dual low side driver in this circuit. Being that these IC’s have a 2 amp rated output the two resistors between the outputs and the switching devices can be sized accordingly to what is best suited to your choice of devices. The IRF2110 IC is also capable of driving transistors as well as IGBTs and power Mosfets by changing the output current limiting resistor values to suit the different switching device circuit requirements.


Power Switching devices.

This circuit is designed to be highly versatile and very forgiving to what type of switching devices that may be used by only having three essential parameter requirements. The first one being that they must have a rated working voltage of at least 4x the peak input voltage. Being that this is a push pull type transformer circuit each device gets subjected to a peak voltage of around 2x the input voltage and a safe overhead of 2x that should be considered a minimum suggested voltage rating. For the current capacity that should also have a minimum of 4x the maximum designed input current due to the general issue that power inverters do have to handle momentary surge currents as load devices are being turned on. The last less critical requirement is that the switching devices are obviously capable of operating at the 30 KHz switching rate. That may not seem like a problem but in the event that this circuit was used to drive multi hundred amp rated IGBT’s, Mosfets or power transistors many of them do not have the capability of running efficiently at a 30 KHz switching frequency so that’s most likely when this limitation would need to be taken into some consideration.


Power transformer.

This is also a surprisingly forgiving component with minimal requirements other than obviously it needs to be rated to handle the power being ran though it and that the primary and secondary voltage ratings are close to correct for what voltages you are working with. The input side is a basic center tap with a recommended AC voltage rating of around ½ to 2/3’s the DC input voltage. The reason for the lower primary voltage rating is due to the PWM systems ability to automatically adjust the output to the voltage the unit is set for. This input voltage mismatch also helps give the automatic voltage regulation system a wider working range relating to low input voltage due to source sag and also to compensate for the losses in the power transformer during peak load events. The best sources for these types of power transformers are common automotive battery chargers with multi volt output ranges or commercial buck/boost power transformers. For a 12 volt power system a transformer with a 12 – 16 volt AC center tapped secondary is recommended. R18, C12, and C13 are optional and are mostly intended to work as additional snubber devices and dampeners to further filter the 30 KHZ carrier frequency out of the output power. C13 is an AC rated power factor correction capacitor that should be sized at roughly 10 uf per KVA at 120 volt output and 5 uf per KVA at 240 volt output.

 

[tcmtech]

Test and tune.​

Given the relative simplicity of each stage of this circuits design there is a limited amount of tuning to be done. The two 555 Timer IC’s need to be fine tuned for 50/50 duty cycles which if you do not have a oscilloscope available they can be initially cheated to produce very slow cycle times by temporarily replacing the timing capacitors and resistors with high value ones that will bring the cycle times up into the many seconds to minutes ranges. From there they can be set accurately just by using a simple clock to time the high and low events of the outputs.

There is also the possibility for some natural DC offset to occur on the power transformer primary due to the variations in the component tolerances. The simplest way to adjust that a basic amp reading of the inverters input current while the 50 or 60 Hz function generator is disabled. At a 30 KHz switching rate a common 50 – 60 cycle power transformer will have a very low idle current. If it does not there is a small DC offset current occurring that is pulling the duty cycle one way or another and that can be easily corrected by adjusting the biasing pot VR4 on U1 until a minimum input current reading is found.

Lastly to get the correct output voltage the signal being fed from U3a is adjustable via VR3. This is in a sense basically turning up the volume on the 50 or 60 Hz sine wave signal. From there the feedback circuit of U3a will try and keep the output voltage of the power transformer level.

If you are looking for a just for the fun of it experiment to try here is an interesting alternate use of this circuit disconnect the 50 or 60 Hz sine wave signal going into VR3 and replace it with an audio signal. This now makes the inverter circuit work as a surprisingly effective and efficient low frequency high power class D audio amplifier!

*Please note that I am not the world’s greatest schematics draftsperson and there is the good chance I could have a resistor or two or a capacitor or two mislabeled. I tried to make sure everything is correctly labeled but still keep it in mind there could be an error or two with my as drawn schematic but more importantly none of these components are set in stone so if you have an alternate component that is available and you can modify the circuit to work with it then by all means do so!

 

[okta]

what the output is pure sine wave?

 

[tcmtech]

Its about as pure as your common utility line power but still way better than the typical square wave that cheap inverter units put out.

 

[bessler]

error

there is a major error in the feedback line of your design .this cirquit can never work properly!!i susspect this circuit has never been build and tested?

 

[tcmtech]

I am not the worlds greatest schematics draftsperson so yes I may have drawn it wrong at some point.

I am open to helpful criticism so if you could point out what you think is incorrect I and many others would appreciate it.

 

[bessler]

the opamp u2a gets a dc level with as you said a aprox sinwave superimposed + input .however the neg input is at 0 via R20 and R19 .the output wil hang on the vcc line (8 v) so there is no closed loop in the feedback.

 

[bessler]

i do think that the circuit is a good base to work on .you cold make it more stable by ading a 47 micro farad cap in the line going to the mass of vr3 so the dc level would always be 4 volts but the 60hetz signal amplitude can be regulated by vr3.there could also be to mutch gain in the circuit round U3a so i should sujest to reduce the gain of u3a and ad a resistor to the + line off 4K7(input -) change r20 to 220k for 220V and ad a cap in serie with r20.so vr1 can then be used for freq control and vr2 for dutycycle.also the choise of the lm1458 as comparator at 30khz seems to me a bit weerd as this is not a very fast opamp .i sudjest to use lm311 since it is a fast comparator and it is around for a long time so it is cheap.your tip on regulating the idle current is very good: ad an ampmeter and ajust for min current by adjusting vr4.i hope these tips help out the guys who want to build this system to a good working device.i have at home a toroid transformer 2 9v windings and output 230v so i could give it a try building thi thing

 

[bessler]

i am not a good drawer https://www.electro-tech-online.com/attachments/555-half-bridge-signwave-power-inverter-2-png.55859/

 

[tcmtech]

I am not sure if you are looking at this in the proper perspective. The output voltage feedback to the negative input of U2a is part of an entire control loop. However unlike a typical power amplifier circuit this is working with a PWM stage in the middle between the input point at U2a and the final output of the circuit which is the secondary power output winding.

Because this works in a very narrow frequency band plus the circuit is all single sided power supply based all the way from the input to the final stage output everything is handled differently than what you would see for a common push pull power amplifier.

As far as what op amp IC's to use that is up to you. In this circuit the highest frequency seen is only 30 KHz which is still well within the working range of a LM1458 op amp IC doing comparator functions.

 

[houston]

Hi. I am looking into the design and want to build the circuit for personal use. can you please tell me what the size of the cap in serie with r20 shoould be if I want 220VAC on the output and also what the frequency of the transformer should be?

 

[lillian]

Hi tecmtec this is a good piece of circuit that I have been searching for for quite a long time now. I want o build the half wave bridge first. Please tell me should i put in the modification with the cap and resistor in my circuit. Do u have a picture of the wave form this circuit puts out. Looking fore your quick reply/.Thank u You can even replt to my email

 

[tcmtech]

If you are referring to the schematic that someone else has with the hand drawn modifications no I would not. Its why I have never commented to any degree on it.

I do not have a photo of the waveforms but what you should see is a reasonably shaped sine wave, although not exactly symmetrical but still it will be close enough to be considered well within the normal range of waveform shape variations you get from the utility lines.

If your output transformer is small and highly efficient you may possibly see the HF steps show up if you have a high enough resolution on your O-scope but they would be very small in comparison to the main waveform.

 

[lillian]

Hello tcmtech thanks for your circuit I would really want to build it today but could you tell me if the correction in the circuit is final and what is the value of the capacitor. Thank you. You can even send a reply to my email also I would be very appreciative. at ayoung_585@yahoo.com

 

[tcmtech]

Thats not my circuit modification. Thats all the info I have on it other than you would have to talk to bessler about why he thinks it should be there and what value he thinks it should be.

Personally I am pretty sure it wont work and will only cause problems. I explained that in a earlier post as well.

 

[lillian]

Hello tcmtech sorry I did not see your reply sooner Thank you . I am not sure on some of the values I cannot see them clearly. Cuold u tell me if these caps are electrolitic caps c5 c6 c7 c8 c2 and c11 whats the value of R17 and R16 and q1. If there is a clearer circuit uploaded somwhere please let me know . I really appreciate your circuit. Waiting for your reply Can this circuit run my washing machine if I build the required watts because my modified sine wave inverter cannot run it. thank u have a great day

 

[tcmtech]

Open the schematic then right click and choose 'save picture as' Then use a photo viewing program to enlarge it all you want.

As far as the washing machine goes I have no idea how much peak power it draws or anything else so I can not say for sure how large this circuit would need to be to run it.

 

[lillian]

Thank you tcmtech for your reply I can see the circuit much better now but the other part of the question is what type of capacitors are the values I asked about . I mean if they are the little disc / ceramic capactors or they are polorised electroltic capacitors
c2 c5 c6 c7 c8 c11 I still dont see a number for Q1 the transistor used to drive the ir2110. When I refer to the washing machine I mean is the sine wave form good enough to run a washing machine in that square wave dont run motors well and your output is sine wave. Thats what i mean . Looking for your reply. Thank u

 

[tcmtech]

For the capacitors electrolytic are fine but any other type that fits the values would do just as well.

For Q1 any common PNP with a gain of 100 or more would be just fine as well.

I intended these designs to be able to be made with any common parts so nothing in this circuit is high precision.