12 V DC to a 220V AC Inverter AMplfier Design

[kachew]

hi au,

i wan to ask u something....do the copper in the pcb board must have a thicker width? since the mosfet drain a quite high current... is about 16 amps....or double for modified sine wave? if it have thinner width will it affect the efficiency of the inverter?
thanks again

 

[audioguru2]

If the copper traces on your pcb are too narrow for the high current then they will burn out like a fuse.

 

[kachew]

dear Au,

i have contruct the circuit and the waveform the oscilloscope is not the expected output i wanted. the output is not a modified square wave instead of square wave only. i attach the waveform for u to view....
can u pls give some opinion on this?? thanks

 

[kachew]

dear au,

1 more question....if the dc power supply used to power the inverter circuit which have maximum 3amperes....can it drive the transformer which have the rating of 8.5-0-8.5V?
thanks

 

[AN920]

Also look what I described in this post
http://www.electronics-lab.com/forum/index.php?topic=10858.0

 

[kachew]

hi an920,

i dont understand the post ... ??? ???

 

[Kevin Weddle]

Hello AN920. Your square wave inverter circuit produces a clock and a clock not? Why does it have so many gates and how does the flip flop help. A flip flop has an extra gate of time delay, which would conflict with that parallel gate.

 

[AN920]

hi an920,

i dont understand the post ... ??? ???

It shows that you can have much better control over the output that a fixed duty cycle drive.

 

[AN920]

Hello AN920. Your square wave inverter circuit produces a clock and a clock not? Why does it have so many gates and how does the flip flop help. A flip flop has an extra gate of time delay, which would conflict with that parallel gate.

I think you are missing the whole point.

 

[audioguru2]

Hi Kachew,
I looked back at 6 pages and I couldn't find the final schematic for your modified sine-wave inverter.The last one had the Mosfets incorrectly connected as source followers.

The CD4047 has a 100Hz clock output, a non-inverted 50Hz output and an inverted 50Hz output. When they are gated and feed the Mosfets then one Mosfet conducts then turns off for a pause, then the other Mosfet conducts then turns off for a pause.

A 3A transformer would allow only 24W of output which is not even enough for it to warm up a little.

Your 'scope shows that the CD4047 is not gated correctly.
Please attach your final schematic.

 

[audioguru2]

I just noticed an Edit that occured a while ago.
Another argument about an ordinary low power Cmos oscillator.

Texas Instruments says that the minimum resistor value should be 10k, not 1k.
The capacitor has AC across it so it should be non-polarized.

1k with 4.7uF is wrong.
47k with 0.1uF is correct for 50Hz and 39k with 0.1uF for 60Hz.

 

[AN920]

The designer thought if the cap can work for a 555 it should be good for this as well 

 

[audioguru2]

The designer thought if the cap can work for a 555 it should be good for this as well 

Yeah. A 555 has a 200mA output current. An ordinary Cmos logic IC has only about 15mA with a 12V supply. A big difference.

What do you think will happen to the two pairs of 2N3055 transistors that must share 50A when the inverter has a 500W load? Each transistor will conduct 25A.
Their absolute max current is 15A each and they saturate poorly over about 10A.

 

[kachew]

dear all,

i think i used the corrected connection for the cd4047 and cd 4001....but i still cant get the require modified sine wave form through it ...is the polarity of the capacitors used affects the result? i hav connected the polarity correctly and use the same value of caps and resistors....my mosfet as source follower? my mosfet in the circuit purposes is just used to drain the current from the batterty through the transformer to ground
so that it will produces a positive voltage on the upper primary windings so do the lower part of the mosfet...if any misconnection pls let me know and any good recommendation for redesign the circuit and to make it works is highly appreciated.....thanks....
i reattach the diagram for u all to view....

 

[audioguru2]

i think i used the corrected connection for the cd4047 and cd 4001

Yes they are fine.

i still cant get the require modified sine wave form through it.

I made your huge schematic smaller and showed where lines cross over and do not join.
Pin 7 of the CD4001 must be connected to ground.
Your CD4047 and CD4001 didn't have +12V.

is the polarity of the capacitors used affects the result?

The two capacitors are non-polarized metalized plastic (Oriental green caps).

my mosfet as source follower? my mosfet in the circuit purposes is just used to drain the current from the battery through the transformer to ground

Your Mosfets are connected properly. Maybe two do not work.

 

[Kevin Weddle]

Hi AN920. I looked at your square wave inverter again. It looks like at 50% duty cycle oscillator, both outputs produce 25% duty cycle. Reducing the duty cycle of the oscillator means that both outputs have even lower duty cycle, and the two waveforms are offset from each other.

Now I am just wondering why there are two mechanisms for lowering the duty cycle. Am I getting your design at all?

 

[AN920]

If you read the description you will notice
a) One adjustment to set the output operating frequency for 50 or 60 Hz inverter
b) One adjustment to set the on-time of each device. On-time can't be more than 50% of total inverter cycle time because of push-pull operation. 

If you use the crystal option your output operating frequecy will be fixed at 50 or 60 Hz.

The waveforms I included shows
1. Drive for a normal fixed duty cycle square wave inverter
2. Typical drive for a modified fixed duty cycle square wave inverter
3. Example of small duty cycle available from circuit.

The advantage of having the adjustable duty cycle allows the use of transformers with non standard winding ratio's and a range of power supplies other than 12V. It also allows you to adjust the final output voltage.

Good reading http://powerelectronics.com/mag/608PET21.pdf

 

[kachew]

hi au,

The two capacitors are non-polarized metalized plastic (Oriental green caps).

this is means the capacitors can be used is ceramic type?

i think without the resistors infront of the mosfet doesnt affect much if the circuit?

y the capacitor and resistor near the transformer is reduced?

 

[audioguru2]

this is means the capacitors can be used is ceramic type?

The frequency determining capacitor should be a 5% (J) metalized plastic type. 10% (K) ceramic is fine for the 0.22uF capacitor.

i think without the resistors infront of the mosfet doesnt affect much if the circuit?

 

[kachew]

dear au,

then the 2 capacitors to be used is metalized plastic type? since there are no 0.22uF capacitors in the circuit.

A resistor is needed in series with the gate of a Mosfet to keep it from oscillating at a very high frequency. Usually 47 ohms is used

so 50Hz of frequency doesnt neccessary to put the resistor in front of the mosfet? since the osc frequency in this circuit is just 50Hz....

the capacitors and resistors used in the circuit is just a protection from the current of the transformer or just use for filtering purposes?