Design Help --- Bubba Oscillator

[BrownOut]

LTSpice is a free download, and you can easily simulate your circuit on it.

 

[audioguru]

You cannot use a sine-wave to make an inverter. Its output transistors will be a linear amplifier and get much too hot and waste a lot of power making heat.

A sine-wave inverter is made by using high frequency PWM switching for the output transistors. The low level PWM modulating signal is a sine-wave.

 

[ismith1984]

audio guru are you saying that me using a bubba oscillator is the wrong approach. maybe you misunderstood, i was trying to say that i was trying to construct a pure sine wave inverter as opposed to a modified sine wave inverter. i probably did wrong in my explanation.

 

[audioguru]

You did not explain anything about your sine-wave inverter circuit so I guessed that it is just an extremely hot linear audio amplifier that wastes a lot of power making heat.

A modified sine-wave inverter is really just a modified square-wave with a step in it. Then it is still a rectangular wave but its peak voltage is almost the same as a sine-wave.

 

[ismith1984]

well i was just talking about my intention to eventually design a pure sine wave inverter. i was asking for guidelines as to go about doing it. i know it has to do with PWM but i just needed a more detailed explanation. meaning i knew the first step was to use an oscillator and presume the next couple of steps has to to with PWM but where do i begin.

 

[audioguru]

You need to learn about PWM or find a teacher.

 

[ismith1984]

hi guys. i know i have been missing in action for a lil bit but i have risen again once more. i have a delimma with my bubba construction in that i am using a quad op amp lm348/324 and i only have one connector for the vcc. my question is how do i connect my vcc considering that the first vcc ( see bubba schematic above) take input on the negative terminal and the remaining three does so on the positive terminal. can i do this connection using just one op amp. any response would be greatly appreciated.

 

[ismith1984]

lm348 configuration is attached.

 

[BrownOut]

Connect Vcc+ to "+" voltage, adn Vcc- to "-" voltage.

I already told you your schematic was connected wrong.

 

[prabhueng]

Hi, ismith1984.

I am also planning to design the 12 VDC to 230 VAC inverter (500W).
So I planned to design the inverter in block by block mode.

The first block is to design the sine wave oscillator for 50Hz generation using the bubba oscillator.

Let start this as a project and share this to all in the world.

 

[ismith1984]

prabhueng did you already design the oscillator to obtain you desired frequency. please let me know.

 

[audioguru]

Most of the world has reliable electricity so we don't use inverters.

If you connect your Bubba sine-wave oscillator to a 500W power amplifier then the amplifier will get extremely hot trying to dissipate 400W! The 12V battery will have a current of 75A. The output transformer will be huge, expensive and heavy.

 

[ismith1984]

audio guru, i dont think this he was thinking of connecting the bubba oscillator directly to the power amplifiers. i am thinking that htis is the first step of the overall project. so hence i think you jumped the bat on that one unless i missed something in this forum. thanks audioguru you expertise is always appreciated.

 

[audioguru]

Now there are two people in this thread who are designing a pure sine-wazve inverter wirh the Bubba sine-wave generator circuit.
ISmith is the one who is making a heater because he said, "my overall project is to build an inverter and so i decided to use the bubba oscillator as it give me greatest stability with the least distortion given the low frequency output required. i next want to amplify the wave to 120V eventually." The amplifier is the heater.

Cheap Chinese pure sine-wave inverters use a small high frequency stepup DC-DC converter using a small lightweight ferrite transformer. Then they switch the high DC voltage with PWM to make a stepped sine-wave that has its high frequency edges tremoved with a small lightweight ferrite LC filter.
One guy opened one and found Mosfets and two PWM ICs by Texas Instruments.

 

[ismith1984]

That showed me i guess! thank you for pointing out that little detail. in any effect i have a request. is there any circuit available that uses a transformer and transistors as switching mechanisms to produce a square wave output of 120 give a 12 DC input. simplicity would be preferred.

 

[audioguru]

The simplest square-wave inverter uses a CD4047 as its push-pull oscillator and it drives two Mosfets that drive a center-tapped transformer.

Many electronic products will not work properly from a square-wave and the simple inverter's voltage will drop with a heavy load and will drop as the battery voltage drops as it runs down. It also needs a low voltage detector to turn off the inverter when the battery voltage gets low.

 

[ismith1984]

by the way. you should know that the input current is limited to 2 amps. not much power is required for load so a low power will still be good.

 

[ismith1984]

i know i am asking too many questions without any having any of them answers but this question is specifically for audioguru. I looked at your revised circuit with the cd4047 chipset and i was wondering if i could use this for my purpose. I need to know whether i can use another chip as i have non available to simulate. also i was wondering whether this circuit could be manipulated so that the input dc voltage be 12V and 2A. if so what changes do i have to make to the circuit and what do you think and approximated output power might be. also, what are the part numbers for the diodes. attached is your inverter for reference.

 

[audioguru]

by the way. you should know that the input current is limited to 2 amps. not much power is required for load so a low power will still be good.

What is your current-limiting circuit?

I need to know whether i can use another chip as i have non available to simulate.

You can make your own CD4047 with about 10 other Cmos logic ICs.

i was wondering whether this circuit could be manipulated so that the input dc voltage be 12V and 2A.

Usually a simple inverter like this is driven from a lead-acid battery that has hundreds of Amps of current available. It uses a fuse for overload protection.

What do you think the approximated output power might be?

My schematic shows 100W max continuous output power. The battery will need to provide 120W (10A). I am just guessing since nobody has built it.
If you limit the battery current to only 2A somehow then the battery power is 24W and the max output power is only about 19W.

The diodes are shown as 2A (or more) diodes. Their voltage rating is 30V or more.

Why bother simulating it? The sim program probably will not show how poor is its performance.

 

[ismith1984]

audioguru as always thank you for your speedy response. I always appreciate it. after much considering i figured out that i dont really need the current to be two amp so 10amps would be just fine. i think i want to construct this circuit i would just need some explanation as to how it works, if not could you point to as to where to look so i could better understand the operations of this circuit. also i am looking fo the data sheet for the cd4047 so i could try to construct it in multisim. any suggestions concerning this would be greatly appreciated.