bubbainverter - Sine Wave Inverter Circuit using Bubba Oscillator

Sine Wave Inverter Circuit using Bubba Oscillator

In this post we learn how to make a simple sine wave inverter using bubba oscillator sine wave generator. The idea ws requested by Mr. Ritwik Naudiyal.
The Request 

Hello Sir!! 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.

thnk u!

bubbainverter 1024x750 1 - Sine Wave Inverter Circuit using Bubba Oscillator

 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 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:

555 pwm waveforms 1024x956 1 - Sine Wave Inverter Circuit using Bubba Oscillator

82 thoughts on “Sine Wave Inverter Circuit using Bubba Oscillator

  1. Have questions? Please feel free to post them through comments! Comments will be moderated and solved ASAP.
    • the TIP transistors are for converting the PWM into high current oscillations so that the transformer primary can be induced with this for the required conversion…diodes are for protecting the transistors from transformer primary reverse back EMF

      R should be 22k according to me…

    • Hello sir, thanx a lot for giving us the circuit for inverter.
      I tried to simulate the circuit . I am not able to figure out how the value of R and C has been decided for frequency 50hz. As 50hz is not coming for 22k and 10n
      according to the formula mentioned in the aforesaid comments!
      Please explain it a bit sir, we have an evaluation for this circuit

  2. Good day,

    Thanks for sharing the circuit to us. There is no batt voltage indicated, does it mean we can use any batt voltage such as 12v x 4batt (in series) = 48v? Does IC 7805 control DC voltage for the generator circuit? This sine wave inverter, does it mean pure sine wave inverter, as per waveform diagram above?
    Thank a lot for explanation.

    • Good day, since the 7805 can tolerate only upto 35V, this voltage cannot be exceeded, however if an alternative method of stabilizing the voltage to the ICs is employed such as a common collector transistor stage, then probably upto 80V can be used in this circuit

  3. I've tried the RC-filtered output generates sine 4017 wive. then be input LM324, LM324 and the output of a square wave instead of a sine wave. if the sine wave input to the LM324, LM324 whether the output sine wave?

  4. This is very helpful for my senior project, so thank you! You explained it in simple terms that are easy to understand, and I appreciate that. My question is: How much power can this circuit provide safely?

    • thanks,
      power of an inverter will be always equal or proportional to the transformer wattage and the AH rating of the battery, provided the mosfets are adequately rated

    • So for example,

      If I need a 75 Watt inverter, I just need to make sure my transformer is rated for at least that much power, and the MOSFET's should be rated for 75 Watts as well? No higher power resistors or other components would be required?

      Thank you!

    • that's correct, and of course the battery AH is also important, which should be around 5 times more the inverter consumption.

      if the batt is 12V, then 75/12 = 6.25…and 6.25 x 5 = 31 AH approximately

    • they serve different functions.

      TIP35 can handle 25 x 100 = 2500 watts with sufficient heatsinking.

      TIP122 can handle 5 x 100 = 500 watts if sufficiently heatsinked.

      However in this design, TIP122s are positioned only for handling the base current of TIP35 and have no direct connection with the load, so no issues, everything is correctly configured…

  5. Hi Again,

    I'm trying to gain an understanding of how this circuit works so I can develop a test plan for it once I build it. How can I configure the IC4017 to generate a 60 Hz switching for the power transistors? Also, I'm a little confused how the sine wave from the bubba oscillator makes it's way to the transformer. I understand that the 4017 switches between the transistors, and the oscillator creates a sine wave, but the in-between steps are a little confusing to me still.

    Thank you!

    • Hi,

      three basic components are required for creating sine equivalent PWMs, viz : an opamp, a relatively fast triangle wave, and a relatively slower triangle wave (or a sinewave)…


      when these two signals are fed across the inputs of an opamp, the resultant at the output produces the required SPWMs.

      here the IC2 becomes the opamp (comparator), pin7 and pin5 becomes its two inputs….fast triangle waves are generated and fed at its pin7 with the help of the square waves through IC1 at IC2 pin#2, and with the help of the associated R/C components at pin#7 of IC2.

      Slow sine waves are achieved through the Bubba circuit and fed to pin#5 of IC2 via the BC547 emitter follower.

      the fast triangle waves at pin#7 and slow sine waves at pin#5 of IC2 are compared internally and an equivalent PWM sine waves corresponding to the bubba output is generated at pin#3 of IC2.

      this PWM is fed at the base of the transistors forcing them to conduct as per the PWM duty cycle, which are in turn are induced across the trafo winding with the same pattern.

      The square wave frequency from IC1 which is fed at pin2 of IC2 is not crucial, and a little here and there does not make a difference therefore we dimension this frequency such that it serves two purpose simultaneously, it modulates the IC2 triangle waves and also feeds the 4017 input to help it to create a frequency at 50Hz or 60 Hz…for 50Hz we tune IC1 to generate 4 x 50 = 200Hz…for 60Hz, it would be 4x 60 = 240 Hz.

      The preset associated with IC1 could be adjusted to achieve this frequency…the value 4 is found by counting the number of sequencing pinouts of the IC 4017

    • The transformer will accept and produce power only within its rated value, it will not accept anything above this regardless of how much the battery or the mosfet are pushing….however the battery voltage must match the trafo voltage otherwise the trafo will burn……also the load should not be beyond the trafo rating or else the trafo might again get damaged..

    • so sir do you mean that the output wattage or power of an inverter in your design is depend on a trafo voltage rating and amp rating… even if you add more power transistor there will no effect on the output wattage…

  6. sir i have tried to solve the 50hz frequency for the bubba oscillator using the formula that you have disscused above by the use of 10k ohms R and a 0.3 C and i convert it into a 0.000003F but the result is really far from the desired frequency which is the result is only 0.0471.

    can you please show me on how to solve it may be the error was from my own solving.

  7. sir its me again In VM planning to simulate this circuit. but i have a question regarding the power transistor above. is the 4 transistor abount need heatsink and it is okay to place the 4 power transistor together in just one heatsink?

  8. question: I always see you use a diode across output fets or transistors to protect them from the back emf from transformers but if I was to parallel the output fets would I need to use 2 diodes for each pair of Fet or would I just use 2 diodes

    • I think a single equivalent diode across any one of the parallel mosfets would do the job, moreover diodes are not designed to work in parallel due to their unequal forward voltage specs.

    • preferably the gates must have there own 10 ohm resistors, the resistor ends could then be connected in parallel….source and drain can be connected directly in parallel across each other

  9. ok thanks, I always wondered if an H-bridge couldnt be done with 4 N channel Fets instead of 2 N channel and 2 P channels… i that link I sent its actaully 4 N channels I dnt know if you have designs like that so I wanted to share so you could try it or prbably you already have designs like that.

    • thanks, yes I already have simpler versions of H-bridge inverters, using n-channel mosfets, moreover the design which you sent will require to be programmed and require a hex code etc.

  10. 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.

  11. 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.

  12. I just tested the circuit without feeding Pwm to the gate of the Fets


    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.

    • 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.

  13. 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.


    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

  14. 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….

  15. 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

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