how best to set up transformer and c-mosfets when building inverter

[JAMES IRVINE]

I am building a dc to ac inverter for a project for a diploma I am using this design **broken link removed** I have two problems number 1 the 2.2uF capacitor I have been given does not resemble the part in the project. It is huge 10 holes on a vera board long and is rated at 100 volts, can anyone tell me will it make any difference to the operation of the circuit as the 2.2uf cap determines frequency amongst other things.

The other problem is, right I've worked out that the four mosfets and the transformer will be located elsewhere other thsan on the same vera board as the controller.
That leaves me not knowing where to begin with that and also not knowing just how these two mosfets are going to be connected to make this complimentary mosfet configuration work.
Any help would be greatly appreciated.

 

[ericgibbs]

I am building a dc to ac inverter for a project for a diploma I am using this design **broken link removed** I have two problems number 1 the 2.2uF capacitor I have been given does not resemble the part in the project. It is huge 10 holes on a vera board long and is rated at 100 volts, can anyone tell me will it make any difference to the operation of the circuit as the 2.2uf cap determines frequency amongst other things.

The other problem is, right I've worked out that the four mosfets and the transformer will be located elsewhere other thsan on the same vera board as the controller.
That leaves me not knowing where to begin with that and also not knowing just how these two mosfets are going to be connected to make this complimentary mosfet configuration work.Any help would be greatly appreciated.

hi,
A 2.2uF tantalum at 6Vwkg [ 0.2inch pitch] would be OK.

I dont follow what you are asking in the second part [blue].?

 

[JAMES IRVINE]

I just mean would I require to use a heavy duty vera board with thicker tracks or something due to the high currents drawn by the mosfets and the transformer. Also I'm not sure how to connect two mosfets together to achieve the complimentary mosfet configuration do I simply connect together the two drains via a piece of wire or something else place them on the same piece of track?

 

[ericgibbs]

I just mean would I require to use a heavy duty vera board with thicker tracks or something due to the high currents drawn by the mosfets and the transformer. Also I'm not sure how to connect two mosfets together to achieve the complimentary mosfet configuration do I simply connect together the two drains via a piece of wire or something else place them on the same piece of track?

hi,
You can mount the FETs etc on a standard piece of strip board and then re-enforce the tracks carrying the heavy current with thick copper wire.

Mount the complimentary FET's on the strip board close together and use thick copper wire to increase the current capacity of the track.

Do you follow.?

 

[audioguru]

It is a very stupid circuit:
It uses 4 Mosfets because its transformer doesn't have a center-tap, then it would need only 2 Mosfets.
2) It uses a very high value capacitor in its oscillator because the resistor value in the oscillator is too low.
The capacitor must be non-polarized but it spec's a tantalum or electrolytic polarized capacitor.

The Mosfets should be mounted on a heatsink with strong wires connecting them to the battery. Small wires are fine to connect the gates of the Mosfets to the Veroboard.

 

[JAMES IRVINE]

Hello Uncle scrooge I dont quite get what you mean by mounting the mosfets on a heat sink, do you mean I need a heat sink to mount through the holes of the mosfets, I really don't have any idea about electronics really so excuse my ignorance for not knowing what you mean.

Also can I use the formula f = 1/( 2.2 x C x R ) to determine the oscillating frequency.

 

[audioguru]

Hello Uncle scrooge I dont quite get what you mean by mounting the mosfets on a heat sink, do you mean I need a heat sink to mount through the holes of the mosfets?

Yes, the Mosfets get hot and must be bolted to a heatsink for cooling. Look at the eficiency. it is 90% at a load of 120W so all 4 Mosfets dissipate about 12W so each one dissipates 3W.
If you use newer and better Mosfets then they conduct better and do not get hot.

Also can I use the formula f = 1/( 2.2 x C x R ) to determine the oscillating frequency.

Yes, that is the formula for a Cmos oscillator.

 

[JAMES IRVINE]

referring to what you said here Uncle scrooge "The Mosfets should be mounted on a heatsink with strong wires connecting them to the battery. Small wires are fine to connect the gates of the Mosfets to the Veroboard."
So I should cut the tracks on the vera board or ensure there is no current flow link with the battery or any other component in the controller except the output and then create a new link between the mosfets and the battery with thicker wire, how thick do you suggest the csa should be.
Also if I stay with the complimentary mosfet configuration if I cant acess another transformer then do I connect the drain to the drain as the diagram **broken link removed** suggests I do or is this not what I do?

 

[audioguru]

Use wires that are thick enough to carry the current.
The schematic shows two sets of complimentary Mosfets driving each end of the transformer winding in push-pull.

Didn't you see the poor performance of this inverter? Without much load its voltage is too high. with a 140W load its voltage is too low.

 

[JAMES IRVINE]

at long as it works uncle scrooge I'm only on a diploma after all, it will work a 60w tv wont it thats my project specification

 

[blueroomelectronics]

You can get a diploma for submitting someone elses work?

 

[audioguru]

I don't know if your TV will work from a square-wave. The peak voltage of the square-wave is much less that the peak voltage of the sine-wave from the mains.

Are you getting a diploma in soldering?

 

[JAMES IRVINE]

well have you any recommendations of any simple modifications, obviously you dont want to tell me because it wouldnt be me working it out but maybe you you could give me a hint or two.

 

[audioguru]

You are making an extremely simple and old inverter circuit. It might light an incandescent light bulb.
Are you going to use its Japanese transistors?

 

[JAMES IRVINE]

I've been given "C1815" they have a "Y OH" on them too. I've also got IRFB11N50A P742XA N-CHANNEL MOSFET and IRF9640 P751XA P-CHANNEL oh well as long as I can point out to them I've been supplied with rubbish tools then I think if anything it shows I'm trying but what type of load could I supply with my rubbish fl 24/6 transformer or do I have to tell them it's useless for any application when it comes to converting dc to ac.

 

[audioguru]

You have been given high voltage low current Mosfets. The inverter needs high current low voltage Mosfets.
The transformer is too small.

All the parts are wrong for that extremely simple circuit.

With the low current Mosfets and tiny transformer then your project might light a 230V 7W night light dimly. I doubt its square-wave would power a clock radio.

Who is doing the project? Them or you?

 

[JAMES IRVINE]

It's a cowboy college who cut corners with everything, well thanks for telling me now I know I need new components, at least now I wont look stupid building it. The thing is I've did a lot on theory, I've more material than anyone on my course so I should at least get a pass and thanks to you now I can get on there nerves by pointing out how they messed up.
Just out of curiosity and ignorance how easy are these components to get from high street shops and how much cost would I be looking at.

 

[audioguru]

You could make this extremely simple inverter for about 5 times the cost of buying a new modern modified sine-wave one that has a lot more power and a display showing the power output and current used. But they are made in China so they might not last very long.

 

[JAMES IRVINE]

Well the college has told me that I should just use a 12 watt light bulb for the load, that will work with a squarewave anyway wont it. Thanks for the info Uncle scrooge, they told me to stick with what I have and stop worrying about it so if it doesnt work it's not my fault. Told you it was a cowboy college.

 

[ericgibbs]

Well the college has told me that I should just use a 12 watt light bulb for the load, that will work with a squarewave anyway wont it. Thanks for the info Uncle scrooge, they told me to stick with what I have and stop worrying about it so if it doesnt work it's not my fault. Told you it was a cowboy college.

hi James,
The 12Watt should be OK for testing, the transformer is 12Vac * 2 = 24VA[watts]

Told you it was a cowboy college.

I hope you win your 'spurs' when you submit your assignment...