# Help Me Understand This Inverter Circuit

Discussion in 'General Electronics Discussion' started by S. M. Rezai Rabbe, Aug 23, 2015.

1. ### S. M. Rezai Rabbe

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Aug 23, 2015
I need to understand this inverter circuit, can someone help me out by letting me know how it is working, I mean how a 12 volt is becoming 220, how the transistors are working.

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,412
2,780
Jan 21, 2010
well, as it's drawn it won't work.

I suspect the positive battery terminal should be connected to the centre tap of the transformer.

This is almost certainly designed to switch 12V from one side to the other of the secondary winding producing a higher voltage on the primary.

This circuit has a number of issues though -- there is no control over the frequency or output voltage, and certainly no protection against overload or over-discharge of the battery.

Since it only applies 12V peak to the secondary, you are likely to only get 220V peak on the output. This is only 70% of normal 220VAC which is about 308V peak.

3. ### TedA

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Sep 26, 2011
Steve is correct, the pictorial diagram omits one of the battery connections.

This sort of circuit has plenty of issues, but it has been much used over the years.

You can learn more by looking-up "Royer oscillator". See the Wikipedia entry.

Are you building hardware, or just making a study of the circuit? Are there requirements the circuit must meet? Where does your project stand now?

The Forum is standing-by with help, if you want to ask questions.

Ted

S. M. Rezai Rabbe likes this.
4. ### S. M. Rezai Rabbe

3
0
Aug 23, 2015
Hey guys, thanks for helping me,
so I have designed the upper circuit in proteus and have a look here, here is the table for the transformer value, what value should I put and what is the calculation for 12 0 12 to 230v AC with a 24 v dc supply

5. ### duke37

5,364
769
Jan 9, 2011
The dropbox does not work for me.

If you run a transformer on double its rated voltage, you will need to double the frequency to limit the core flux.

6. ### TedA

156
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Sep 26, 2011
The Dropbox links worked for me.

But I can't really read the text on the schematic. Are the resistors 2.2k ohms?

If there are no requirements at all, we could assume that the posted schematic and circuit values constitute most of the constraints, but we will still have to assume some things, such as the desired operating frequency range.

If the project is to involve actual hardware, do you have access to an engineering lab? Any instruments or test equipment at all?

Do you have a datasheet for the 2N3055 at hand?

If you have the applied AC voltage, frequency, and inductance values, can you calculate the resulting AC current?

Does your transformer model include any non-linear characteristics? Anything to do with core saturation?

It is usual for Royster oscillators to be operated with the transformer core starting to saturate each half cycle. If your simulation software does not model transformer saturation effects, you might need to add external non-linear networks, perhaps including some zener diodes and resistors, to approximate the real world transformer a little better.

The circuit will still oscillate if the current is so low that the transformer never saturates. But it will be quite sensitive to any load, and to imbalances between the transistors and resistors.

You want to choose the transformer winding inductance values to make the magnetization current small relative to the operating current under load. The ratio between the inductance values will be the square of the turns ratio.

This circuit will automatically adjust the frequency to suit itself. Putting 24V across a winding intended for 12VAC can be OK, as long as the resulting higher frequency is not a problem. ( And a long as the insulation is not over-stressed.)

Ted

7. ### TedA

156
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Sep 26, 2011
PS: I just realized that my zener network notion is rubbish. You need a network that responds to current, or to voltage times time, to simulate the transformer core saturation. A current limiter in the +24 line might work well enough, also.