12 V DC to a 220V AC Inverter AMplfier Design

[audioguru2]

The efficiency is very high, maybe 95% with good Mosfets:
1) One Mosfet is on.
2) Both Mosfets are off.
3) The 2nd Mosfet is on.
4) Both Mosfets are off.
Repeat.

When a Mosfet is on then it has a very low voltage across it so its wasted power is low.
When both Mosfets are off then no power is wasted.

 

[Morro]

hi audioguru,

MOV is used to protect circuits against excessive transient voltages and how about the output overloading protection?? as i know many inverter nowadays have that function  : :

 

[audioguru2]

MOVs work very well to clamp voltage transients. But only until they burn out.
This simple circuit uses a fuse for overload protection. I don't know if the transistors will survive long enough for the fuse to blow.

 

[Morro]

hi audioguru,

i see the datasheet of the mosfet of IRF540, if the ic CD4047 produces output of 5V the the Vds would be 7.5A from the mosfet. ??? ??? i still cant think of how to supply the 10V to the transformer? is it from the +5 and -5V from the IC??? how do the mosfet do its job??? thanks for your reply :-[

 

[audioguru2]

Hi Morro,
The IRF540 Mosfet is pretty old so has a fairly high on-resistance compared to newer Mosfets. Therefore they will get hot in a powerful inverter.

The CD4047 is Cmos with a supply voltage rating up to 18V. It doesn't need a supply of only 5V like old TTL logic chips, it works fine from 12V and can directly drive 12V to the gates of the Mosfets in a square-wave inverter so that they turn on as hard as they can.
If you are talking about a modified sine-wave inverter then the CD4001 logic gates are also Cmos and can have a 12V supply to directly drive the gates of the Mosfets with 12V.

The center-tap of the transformer is connected to +12V. Then the Mosfets ground one side alternately. There is not a -5V.

 

[Morro]

hi audioguru,
but i saw the thread here stated that the modified sinewave inverter by kachew is 10V-0-10V...can it be feed in the 12V from the IC??? and it should be having loses of 1V from the mosfet in parallel... :-\ :-\
thanks for your reply

 

[audioguru2]

Hi Morro,
The peak voltage of a sine-wave is 1.414 times its RMS value. Its RMS value is the same as the peak voltage of a square-wave. So the peak voltage of a modified sine-wave inverter must be higher than if it is a square-wave inverter.

The fully charged car battery is 13.8V and the Mosfets have a loss of about 1V. Therefore the remaining 12.8V into the 10V winding of a transformer produces close to the correct peak voltage for a sine-wave.

 

[kachew]

hi audioguru,

i think there is some problem due to the circuit....i think the CD4047 and CD4001 can be act as the control circuit for the swithing circuit which must consist of four mosfet in order to get the modified sine wave?? in the 1st cycle the signal from the control circuit will go trough the 1st then to the 1st winding of the transformer and back to 4th mosfet to get the +12V at the transformer and get the positive pulse at the output of the transfomer. in the 2nd cycle, the signal from the control signal again pass through the 2nd and 3rd mosfet again to get the negative pulse at the output of the transformer....
pls comment and thanks for your reply

View attachment 39676

 

[audioguru2]

Hi Kachew,
The center-tap on the transformer is supposed to be used to power the Mosfets while they conduct on each side alternately. Then each end of the transformer's winding is supposed to be driven by the drain of a Mosfet for the full battery voltage to be applied to the half of the winding.

You are using the Mosfets as followers since the transformer is at their sources. So when the logic drives a Mosfet's gate to +12V then the source follows to only about +2V. But then the other end of the winding isn't connected to anything (a turned-off Mosfet) so no current flows in the transformer.

Let the 1st side conduct on its pulse, then a pause while nothing conducts, then the other side conducts, then another pause when nothing conducts.

View attachment 39677

 

[kachew]

hi audioguru,

then what u means is the mosfet will only produce only 2V from each mosfet to the transformer so the is unactive in this circuit? then the previous kachew inverter is theoritical working (exclude latest modification) and the mosfet is acts as a switch?? and for 200w output the transformer have to be 12V and 1Amps??
thanks for your reply.

 

[audioguru2]

then what u means is the mosfet will only produce only 2V from each mosfet to the transformer

Yes. An N-channel Mosfet is turned on by making its gate about +10V higher than its source. Your circuit had the input going to +12V from the 4001 gate, so its source which is connected to the transformer goes up to only +2V.

so the is unactive in this circuit?

The other end of the transformer winding is connected to a turned-off Mosfet, so no current flows and the circuit does nothing.

then the previous kachew inverter is theoritical working (exclude latest modification) and the mosfet is acts as a switch??

Yes, it was correct since the transformer's center-tap connected to +12V and the drains of the Mosfets pulled their side of the transformer's winding to ground.

and for 200w output the transformer have to be 12V and 1Amps??

No. 12V and 1A is only 12W. Your transformer must be 200W for the output plus maybe 40W for heating the circuit, and must be 10V to make the peak voltage of the modified sine-wave high enough. So the transformer must be 10V-0-10V at 240VA which is 24A. A BIG transformer.

 

[kachew]

hi audioguru,
i think i know what is kachew tryin to deliver.... ;D the concept can be found in any power electronics book ;D ;D and i also attach a circuit i think is similar to your concept using the cd 4001....and audioguru can u try to explain your circuit using the cd 4001 and mosfet as a switch?  the center tap transformer is similar to 2 transformer circuit as i attach? thanks for your information and reply ;D ;D

Figure.rar

 

[kachew]

sorry to introduce myself, actually i am using kachew's account , i am sonny....

 

[audioguru2]

Hi Sonny,
You make everything very confusing when you use Kachew's account. You should register on this site as yourself. Then login as yourself each time.

You attached a DOC file instead of a GIF or PNG file for your schematics, and you compressed it as a RAR. Just attach the schematics as a GIF or as a PNG.

The CD4047 has an oscillator output and has two opposing Q and Q-not outputs which are the oscillator divided by 2. When you gate those outputs with CD4001 NOR gates then the outputs of the gates drive Mosfets with the correct timing for a modified sine-wave inverter.

View attachment 39696

 

[kachew]

hi audioguru,
may i know the transition of the pulse where both mosfet are turned off? you only shows the transition where 1st and second mosfet are turned on....and i would also like to ask why we want to use the drain source of the mosfet to ground the center tap transformer?
thanks for your reply

 

[audioguru2]

may i know the transition of the pulse where both mosfet are turned off?

I showed it a few days ago. Here it is again clearer.

why we want to use the drain source of the mosfet to ground the center tap transformer?

What is a drain source? A Mosfet has a drain pin and a source pin. On these N-channel Mosfets, the sources are connected to ground and the drains are connected to the ends of the transformer winding. The center-tap is connected to +12V. Here is your schematic.View attachment 39699

View attachment 39700

 

[Morro]

hi audioguru and kachew,
its seems this topic become more complicated......i just want to ask is this inverter runs by 12vdc (input from 12V battery) and having ouput 240vac at the transformer output(output of circuit at the transformer secondary winding)? as i understand the transformer operates on Ac current and from the diagram as i understood this Ac current provided by 12 battery dc source and being switched by the mosfet to produce 12 to 0v alternating step current? is this correct?? ;D ;D as i understand the transformer cant be fed from a 12 dc battery directly....pls advice...
thanks for your reply.... ;D ;D

 

[audioguru2]

Hi Morro,
The transformer is fed with AC from the Mosfets..
One side of the center-tapped low voltage winding has 12VDC applied to it from the Mosfets on that side, then that side turns off and the other side turns on, for a square-wave inverter. The DC current in the winding alternates from side to side. That makes AC in the high voltage winding of the transformer.

For a modified sine-wave inverter, there is a pause with no current between each side being driven alternately. The modified sine-wave inverter doesn't feed a stepped current to the transformer. It is 1 side on, then a pause with no current, then the 2nd side on, then a pause with no current, then it repeats. The DC current in the winding alternates from side to side. That makes AC in the high voltage winding of the transformer.

 

[transapax]

hi audio guru,
  i now understand why you are called by that name. you answers are flawless. can u please help me answer the following questions?;

1. what are the functions of the two 1n5408 diodes connected back to back from the drain of the power mosfets to ground?.

2. can i achieve a back emf suppression by connecting the two diodes front to front and connect their cathodes to the positive of the battery?

3. lastly, is there no way one can connect a feedback to the cd 4047 to achieve a good voltage regulation as in sasi's sg3524 pwm inverter circuit?

 

[audioguru2]

1. what are the functions of the two 1n5408 diodes connected back to back from the drain of the power mosfets to ground?

They are to protect against reverse-voltage spikes. But Mosfets already have diodes in them which is how they are made so I wouldn't add the 1N5408 diodes. Look at the diodes (zener diodes) in an IRF540 Mosfet.

2. can i achieve a back emf suppression by connecting the two diodes front to front and connect their cathodes to the positive of the battery?

That would cause smoke. When one side of the center-tapped transformer winding is grounded by a turned on Mosfet, then the other side must swing up to double the supply voltage due to transformer action (think about a teeter-totter). Your added diodes would short-circuit the voltage swing.

3. lastly, is there no way one can connect a feedback to the cd 4047 to achieve a good voltage regulation as in sasi's sg3524 pwm inverter circuit?

Not easily. The SG3524 is made to vary the pulse width by feedback but the simple CD4047 is not.View attachment 39713