Hero999

The circuit is quite reliable when properly designed and built. This sort of circuit has been used to power fluorescent lamps of DC power in busses, trains and military vehicles for years without any problems.

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HS3

I know this is an old post but I believe this is fundamentally wrong.

Speaking of forward mode transformers (not flyback) and assuming the transformer is designed so that it does not saturate in any case, then the addition of a DC current at the input does not affect the output at all and, in fact, there is NO way to tell by looking at the output if there was a DC component in the input.

Look at the output transformer of a valve amplifier. It is carrying the plate DC with the output signal superimposed. The output is the AC signal with no DC. If I give you the output of two transformers and both give the same signal you cannot know which one is carrying DC in its primary. If the input is V = K + A sin(ω*t) The output will always be the same regardless of whether K is zero, positive or negative.

The thing is that if you are carrying DC in the primary then you need a bigger transformer so it does not saturate the core. The DC current is creating a continuous flux which takes the core nearer to saturation so transformers (and chokes) which carry DC in their primaries need to be specially designed but you cannot see any difference in their outputs. None whatsoever. The DC is totally blocked and it is as if it did not exist.

Just the same happens with a capacitor. If I have a signal input blocked by a capacitor, on my side I will see the AC variations but I have no idea from this side what the voltage may be on the other side of the capacitor. To know that I have to go to the other side of the capacitor. All I can see is the AC from my side.

audioguru

Good point.

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Hero999

The circuit I am critisising is a flyback so the core does saturate. What you're saying is true that there's no DC on the secondary but there will be just negative DC pulses and no positive pulses.

I've uses a similar circuit to run a fluroscent tube from before and after a few hours of running only one end of the tube went black. This is because the current only flowed in one direction causing the cathode electrode to sputter on to the glass. Try connecting a neon lamp to this circuit and you'll see that only one electrode will glow.

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Ubergeek63

Hero, is that guy a bit full of himself or what? In the industry that circuit is called a royer inverter and was the standard inverter circuit for many, many years.

For him to say that he improved it is quite presumptuous. There has been nothing under the sun original that could be done with that circuit for almost as many years.