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My 120 Watts Power Inverter


Guest Kasamiko
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Guest Kasamiko

This is the Power Inverter I been talking about in the other forum..
The attached zip file contains the schematic in .GIF format

to MP,
Please resize it to suit the forum..
Thanks you.

Any suggestion,modification and comments are very welcome!!

120Watts_Inverter.zip

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Guest Kasamiko

Here it is..Take a look and give comments..BAD or GOOD.. ;D
or modifications and improvement..

MP,
Please resize it to suit the forum..It is already in .GIF format thanks again..

120Watts_Inverter_th.gif

click on image for high resolution

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Hi Kasamiko,
That's a nice design. But the oscillator/flip-flop is rather complex and U2 is operating at a supply voltage that far exceeds its rating. The 4047 from the other project is better suited here.
The MJ15015s are expensive and your circuit doesn't need its high ratings, except it can use a smaller heat-sink than its 2N3055 cousin. 2N3055s should work fine here since it has the same gain and current ratings.
I couldn't find data sheets for 2N6124 nor MA21 so I don't know if they are OK.
I haven't fully analysed spike protection, but the low values for R12 and R13 is a clever way to protct the output transistors against base-emitter avalanching.

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Kasamiko,
Oh, oh, I see a problem:
1) When one transformer wire is pulled up to 11V by its conducting output transistor, then the other transformer wire is forced to -11V by center-tapped transformer action.
2) The output transistor that has its emitter forced negative, should be turned-off, but current will flow into its base from R9 or R10, which will cause it to turn-on.
3) This will waste power and create unnecessary heat.
If you increase the value of R9 and R10 to 1.5K, then the above problem will not occur, with no other consequences.
It looks like the output transistors will protect all devices from spikes, since a positive spike at one transformer wire will create a negative spike at the other transformer wire, which will turn-on that transistor (as above), arresting the spike. But the output transistor may not turn-on fast enough. Try it and see.

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Guest Kasamiko

I'll try your suggestion..
74LS74 is actually DM74HC74 which is a CMOS device that will handle 12V supply. I encountered a problem with TI CD74HC74 but upon looking at there datasheet I found out that they only operate at maximum of 6 VDC!!
2N6124 = NA52,2SD313,D1061
= PNP 40W 45V 2.5Mhz 4A (TO-220)

NA21 NPN 0.6W 20V 50Mhz 1.5A Audio Output (TO-92)

I think the single 4047 will serve the function of U1 and U2..
What can you say?? ??? ???

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Kasamiko,
Your 2N6124 and MA21 transistors should be OK.
I couldn't find a data-sheet for a DM74HC74, but all "HC" chips that I have seen have a maximum operating voltage of only 6V.
"LS" and "HC" chips are made for extremely high speed so why use them here? An ordinary old 74C74 or 4013 will work fine and run with up to 15V. But it is best to use the 4047.
Don't forget to change R9 and R10.
Are you going to replace the MJ15015s with 2N3055s?

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Guest Kasamiko

I'll change the oscillator and divider circuit with a single 4047 to simplify the design..and yes R9, R10 and the MJ15015 too.. ;D
do you think a single pair of 2N3055 will do the job of MJ15015 at 120 Watts??
I'll be finishing a new PCB for it.. ;D
Thanks for the ideas..

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Guest Kasamiko

The unit is working will now!!! ;D
with 2N3055 driving the transformer..I connected it to an 85 Watts, 14" CTV, operate it for 2 hours continously and the output transistors are cool to touch..
But there are certain models of tv that some noise appear on the screen.. I solved that by adding a 330R, 10Watts resistor in series with two 0.47uF/450V mylar capacitors and connect it in parallel to the 220 output..
That's all for now..

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Kasamiko,
I'm glad to hear that your circuit works well.
It should be good for 180W with a 24V CT, 7.5A transformer and if all the transistors don't get hot.
How did you heatsink them? One heatsink for all drivers and outputs? What size?
That is good for you to use a "snubber" circuit across the output to eliminate interference.

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Guest Kasamiko

I put the two 2N3055 into a common heatsink/chassis without any insulator (since there collectors are tied to B+, That makes my chassis to B+ potential.. ;D) The twodriver transistors, 2N6124 are all mounted vertically in the PCB without any heatsinks. What concerned my is the two 47R, 5 Watts resistors (R8 and R11) They tend to generate a lot of heat and the portion of PCB where they are mounted are starting to char.. :o
I'm planning to install them off the board on my metal case..
That's all for now..
Regards.

Rhonn

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Kasamiko,
With 11V across the 47 ohm resistors, half the time, the power dissipated is only about 1.25W. Maybe they are small and normally reach a very, very high temperature at their maximum rating (5W) so therefore get hot at 1/4 of their rating.
Try physically larger or higher power rating (10W) resistors.

I looked for driver transistors having more gain (so that these resistors can have a much higher value and less power), without luck. You can't use darlington drivers without losing output voltage and increasing the heating of the output transistors.

For the next circuit try a 4047 directly driving the gates of N-channel power MOSFETs with their sources grounded and the transformer's center-tap to +12V. 300W output should be easy by using one pair.

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Guest Kasamiko

That sounds great!! but I have a parts availability problem when it comes to MOSFET's.. :'( :'(
and i'm not comfortable working with it.. :-[ :-[
Maybe.. when I can have it locally, but not for now..

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  • 2 months later...
Guest Kasamiko

Screen captured waveform of my 120 Watts power inverter from the output of drive transistor.
Using WINSCOPE 2.51

(Sorry I only saw the waveform as SQUARE WAVE, but I can't read it. amplitude,frequency etc..)

Rhonn ;) ;)

post-0-14279141698094_thumb.jpg

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hey i got the same circuit but i;ve encounter a different problem. first i bought the 74hc74, then when i tested the circuit , it does not work. i replaced it with the 74ls74 then it works. the problem is when i measured the ouput ac voltage it's over 400v. i only tested it with llights and then it works ,does the over voltage affects, i used a 12v motorcycle battery as dc source..

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Guys congratulations for the project
i only want to see the whole project with all the adjustments you made
i mean the replies ended and if someone wants to build the circuit , he must read the whole article and fix the things that must be changed

resend the final version with schematic

THANK you very much!!!

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