In this post I have explained how to make a simple sine wave inverter using bubba oscillator sine wave generator. The idea ws requested by Mr. Ritwik Naudiyal.
Technical Specifications
I am a 4th year B.Tech Student Electrical Eng.
We are trying to make pure wave sine wave inverter using PWM and bubba oscillator for our Final project, also along with it a battery charging and auto cut off circuit would be needed
We want the inverter to work for day to day purposes. We would be grateful to you if u can give a working circuit fr this.
thank You!
Circuit Diagram
NOTE: Please use a Darlingtton pair for the BC547 connected with pin#5 of IC2 for efficient PWM conversion.
The Design
The proposed sine wave inverter using bubba oscillator may be understood with the help of the following points:
The stage comprising two 555 ICs are configured as PWM generators where IC1 forms a square pulse generator for the PWMs while IC2 forms the monostable PWM generator with respect to the modulation input applied at its pin5.
The sine wave modulation input at pin5 of IC2 is ahieved with the help of a bubba oscillator created by using four opamps from the IC LM324.
The generated sine wave pulses are fixed at precise 50 Hz and fed to pin5 of IC2 via a BJT common collector for further processing.
The 50 Hz Formula
The 50 Hz for the bubba oscillator is set by selecting R precisely with the help of the following formula:
f = 1/2(3.14)RC
IC2 compares the sine wave modulations at its pin5 with the square pulses at its pin2 and generates an equivalent PWM waveform at its pin3.
The flip flop stage reqired for switching the power stage is configured through a single IC 4017 whose outputs are appropriately integarted with the two high gain high current power BJT stage formed by Darlington TIP122 and TIP35.
The pin14 of the 4017 is clocked at around 200 Hz via pin3 of IC1 in order to achieve a 50 HZ switching across the power transistors.
The PWM modulation of the above 50 Hz switching is implemented with the help of the two 1N4148 diodes connected across the bases of the tIP122 and are switched in accordance with the PWM from pin3 of IC1
Assumed waveforms of the PWMs may be referred in the following image:
Waveform Bubba Oscillator
Questions & Answers
1. What is it’s power rating?
2. How do I increase the output power, if I need to?
Power rating can be adjusted by upgrading the TIP35 rating, or using MOSFETs instead.
How can I use egs002 with out shot down and blinking
I think those are in-built features of the board and it cannot be removed or disabled.
To me the bubba circuit is just a west because pin five of a 555 timer ic is the output control pin which a may voltage feeding into the pin will do same work that bubba circuit is doing
Ic3(cd4017) in the above circuit being a counter, did not work in one of the inverter circuit I tried it with. what if I replace it with cd4013 will it work as intended.?
Thanks in advance.
4017 is s perfect IC for inveter application, you can also try 4013, but if 4017 did not work then 4013 won’t work either for you.
You can see the first two examples in the below given link:
https://www.homemade-circuits.com/modified-sine-wave-inverter-circuit-2/
Swagatam,
Thank you for your response to my suggestions and observations and I visited the site you requested me to go to which confirms the original configuration.
Since my last e-mail I have now done some extensive tests on the Bubba oscillator circuit and have come to the following conclusions.
Bubba oscillators work well at higher frequencies i.e. in the kHz range, however, when you start to ask them to work at lower frequencies it is necessary to increase the value of the timing resistors (R). Because Op.Amps are not known for their amplification characteristics the increased resistance together with the 360K resistor blocks the signal path and the circuit does not oscillate. Removing the 360K resistor i.e. shorting it out reduces the effective overall resistance and it begins to work.
In my tests I have found that a preferred value of 27K for (R) is as close as you are going to get to 50Hz and the oscillator produces an output of around 51-52Hz. Obviously you could replace the resistors with trim pots but this would then require accurate measurement and adjustment which I do not think is worth it. The mains frequency on the grid is drifting about anyway and a few Hz is not going to make much difference to the output of the inverter.
You could tighten the tolerances of the resistors (R) but I think that this would be overkill.
Taking out the 360K resistor produces a displacement of the phase shift in the circuit with the result that the sine wave now appears at Pin 2 and not Pin 12 in the original configuration but the sine wave is of good quality and reasonable amplitude.
I hope that my contribution is of assistance
Thank you very much Paul, I appreciate the valuable information that you have shared here, I am sure the other visitors will find this useful too!
I very much enjoy your circuit ideas but I would like to raise one or two comments about the Bubba oscillator included in one of your inverter circuits.
Firstly according to the circuit the timing capacitors should be 10nF is this an error as in all other circuits I have seen they are 100nF?
Secondly I found that the circuit would not oscillate unless the 350K resistor was removed. The resistor value appears to be correct as it appears in other circuits I have seen.
When this is done and the capacitors change to 100nF it begins to oscillate and with 27K resistors it give an output of around 51HZ which is as close as I can get with preferred value resistors.
However, interestingly enough the sine wave now emerges from Pin2 of the OP AMPs and not 12 as in the circuit. I know that it is phase shifting because I get a cosine wave at one point and a square wave at another.
Do you have any suggestions why this should be?
Thank you for the suggestions, you may be correct….Actually the bubba circuit was taken from some other source, so i am not sure about its accuracy.
For accurate bubba circuit calculations you can refer to the following article, which can be applied in the above sine wave inverter design:
https://www.homemade-circuits.com/phase-shift-oscillators-wien-bridge-buffered-quadrature-bubba/
Can I replace the cd4017 with sg3524
yes you can!
Thanks sir,
Can I build a 3000-4000watts inverter with this circuit? Can I use 24v battery input for such power?
Hi foxy, you can definitely do it by appropriately upgrading the mosfet and the transformer specs.
Hi I have tried to simulate the circuit as it is, on proteus, but I am not getting any output from the bubba oscillator and hence none from th tx.I have tried to attach the circuit on email but I am not sure if it will be received.
Hi, I am sorry I can’t troubleshoot simulator results, but I can assure you that if you build this practically and correctly it will work, 100%
Hi what is the output power and current for this? What kind of loads can it drive?
Thank you.I really appreciate that you actually respond to all of the questions and your circuits are very useful for my project.
You are most welcome Claudia!
It will depend on the transformer wattage rating, and battery Ah rating. Mosfets can be replaced as per these maximum wattage ratings.
Load can be any type of load
SHOW DE BOLA
circuitos otimos ´muito bom
Thank you!!
Hola Swagatam estoy intentando por todos lado hacer esta montaje oscilador bubba pero no funciona los Ic1 y Ic2 que pulso deben tener y he cambiado las R y los C del IC4 pero nada
por favor puede usted ayudarme si hay otro circuito o como mejoro este diagrama
Gracias
Hola Victor, could you please translate your comment in English so that we can all understand it?…
ok as I said previously from the 2 pins from the micro-controller I am getting 50hz, but when I connect the meter to the secondary of the transformer I get 1.8khz and 3khz from the secondary, I was just asking what could cause that, when I removed Pwm feed what I actually did was to disconnect the wire connected to the gate of the Fets in which I got 51hz.
So i was wondering what the problem could be but I understand that you didnt design it I just like to try new circuits and was just seeking advice on fixing that problem.
if the transformer primary is oscillating at 50 Hz then the secondary would oscillate at the same rate too, I think your frequency meter could be malfunctioning, check your home AC outlet frequency with the same meter, see whether it shows 50Hz or some other value….
I realize why you didn't understand fully what I was saying, I sent this link to you but seems It didn't go through at the beginning of the messages.
https://www.dropbox.com/sh/6di2i4tvak0g7d1/AAC2HNF3qCmzU85XvVRFIPXya?dl=0
thats the schematic I was trying and was asking for your assistance.
I got 51hz without PWM feeds to gates of Fets
But while the Pwm is disconnected from the Fets if I connect the transformer there is no frequency at the drain of the transistors nor at the secondary of the transformer, also no voltage across the drains which would go to the secondary of the transformer.
If I connect the transformer and also reconnect the Pwm feeds then the frequency goes up to 2.5 or up to 3khz on the secondary of the transformer and and the primary frequency is 1.8khz. and at that time I would get 10.8v accross the drains of the FETS.
It will be difficult for me to comment on the linked circuit since it's not designed by me and it's based on Microcontroller.
By the way I cannot see any PWM feed from the IC, it's just the alternate square wave outputs which are been fed to the half bridge drivers. so if you are disabling this the entire driver circuit is going to shut down
One other thing, I don't have any 10ohms resistors so I used 220ohms for the gate of the fets could that be what's causing the high frequency.
I am assuming that you have built the circuit discussed in the above "bubba sine wave" article.
if you are getting 50 Hz at the gate of the mosfet or power transistor then the transformer should produce the required AC and frequency at the output…
gate resistance may not be the cause, still try using smaller resistances below 50 Ohms instead of 220 ohms.
connect a load at the trafo output with this 50 Hz operation without PWM and check the response
I just tested the circuit without feeding Pwm to the gate of the Fets
https://www.dropbox.com/sc/eg05wv8wdk1wr99/AAAmZ-qwYG-SRHcHdqDG_hY0a
I got 51hz
But while the Pwm is disconnected from the Fets if I connect the transformer there is no frequency at the drain of the transistors nor at the secondary of the transformer.
If I connect the transformer and also reconnect the Pwm feeds then the frequency goes up to 2.5 or up to 3khz on the secondary of the transformer and and the primary frequency is 1.8khz.
The pics I sent you were from the test I made before you replied so the PWM section was still applied to the gate of the FETS I will remove them now and send results soon.
Also the more I change the time division on the scope it's either the frequency doesn't show or it changes in value so that's why I used my multimeter to test frequency.
check the frequency without the PWM feed at the base of the transistors, it should now show 50Hz, if not then either the IC1 is wrongly set or your meter could be malfunctioning
A similar circuit was verified for its waveform by one of the readers, where he could capture the details across the output of the trafo, you can see the images in this article….so it think the results would be quite similar for the above design too
https://www.homemade-circuits.com/2013/10/modified-sine-wave-inverter-circuit.html
I am having difficulty in understanding your waveform results….
sorry, I am assuming you have applied the PWM section as described in the above article, did you? if not then the above linked article and my suggestions could be irrelevant for your case and the issue can be somewhere else…
OK the scope I have is a portable scope do nano
I'll provide a drop box link to the set up I have and the readings, also the scope is connected to the primary of the transformer because I don't think it can handle 250v
https://www.dropbox.com/sc/g741oldx01s7cu6/AAA6iCJQXNQo-ZafHuOUSNpIa
I actually built the circuit in the link I provided above and from the arduino I got 50hz but from the transformers output I got 2khz, I am wondering what would cause that I used the correct value capacitors, 2 diodes are there that has no value so I used 1n4007.
I was thinking about building a low pass filter to get 50hz which I would just use a 330 ohm resistor and a 10uf capacitor but I was seeking your advice to identify the problem causing that high frequency.
It's causing due to the superimposition of the PWM frequency over the 50Hz pulses, please check through an oscilloscope for understanding the exact situation of the output….using the low pass will simply block the PWMs.
PLease what is the standard rating for the transformer
what is the standard load you would be using?
Oh kool Ill give it a try, is it PWM?
it's a simple square wave design, however PWM could be inserted across the low side mosfet gates
I know you have H bridge with N channel fets but I thought it was a mixture of N and P…
Also I know the circuit needs to be programmed I have the code for it also, I ordered the driver chips so when they arrive I'm going to build it and test it out with 4 irfz44n, if that works I'll try 8.
I was referring to this circuit:
https://www.homemade-circuits.com/2014/01/simplest-full-bridge-inverter-circuit.html
the "load" could be replaced with a transformer for the required output