# help me understand this circuit

Discussion in 'General Electronics Chat' started by syaf921, Feb 14, 2013.

1. ### syaf921 Thread Starter New Member

Dec 21, 2012
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0
How this circuit functioning?
This is Inverter 100W by IC 4047 + 2N3055.

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2. ### #12 Expert

Nov 30, 2010
16,704
7,354
How do you think it is functioning? Have you looked up the chip to see what it does?

3. ### Jaguarjoe Active Member

Apr 7, 2010
770
90
If it has a 1/2 amp fuse and 12v input and P = E x I, that's going to be 6 watts or less going in. How is this a 100 watt inverter? You can not put in 6 watts and magically get 100 out.
Even if the decimal point was wrong, a 5A fuse will only be 60w or less. Maybe it's 10A?

4. ### thatoneguy AAC Fanatic!

Feb 19, 2009
6,357
718
That circuit will not work as shown.

Buy an inverter that matches your needs.

Issues:

• Output is Square Wave, a big efficiency loss in transformer
• Frequency not controlled
• VCE drop of transistors causes a lot of heat and even less efficiency.
• 12V - 220V is a 20x increase in voltage, and a 1/20th loss in current
• After subtracting the roughly 50% losses, Getting 5W from 220V side would be astounding.
Is your transformer rated for 2.5-4 kVA?

If those are the only components you have access to, feel free to try, but don't expect much, and have a lot of fuses on hand.

5. ### SPQR Member

Nov 4, 2011
379
48
I'm asking this question out of ignorance, not out of disagreement.
Don't the pot (VR1) and cap (CX) control the frequency of the chip?
Or are you thinking about a "higher level" frequency control?
Thanks

6. ### THE_RB AAC Fanatic!

Feb 11, 2008
5,435
1,305
It's a pretty nasty "inverter" for sure!

I particularly like the "0.5A" fuse on the 12v supply. They are not being optimistic about power output.

Now why it needs 2 paralleled massive 2N3055 transistors, to switch 12v <0.5A is another mystery.

7. ### thatoneguy AAC Fanatic!

Feb 19, 2009
6,357
718
The frequency will drift with temp when using an RC time. It's not like most small things today even care, though.

8. ### bertus Administrator

Apr 5, 2008
15,805
2,389
Hello,

The way that the transitors Q3 to Q6 are connected is very odd.
The transistors are not correctly connected to work in parallel.
The base connections of Q3 and Q4 are at the same level.
Also the base connections of Q5 and Q6 are at the same level.

Bertus

9. ### SPQR Member

Nov 4, 2011
379
48
Gotcha!
RC circuit vs a crystal circuit.
Thanks!

10. ### THE_RB AAC Fanatic!

Feb 11, 2008
5,435
1,305
Yeah that's a schematic fault (along with the others). The 2N3055's are supposed to be in paralleled pairs, similar to a lot of other simple inverter designs.

That schematic doesn't inspire confidence does it?