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 Post subject: New, Old Output Stage
PostPosted: Mon Jul 21, 2008 10:08 am 
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Sheep

Joined: Sat Dec 23, 2006 8:27 pm
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Location: NAC
I have a power supply design that I call the flyback buster. I see it as a way to get the single ended drive and subsequent simplicity of the flyback approach without worry about exceeding the D-S breakdown voltage of transistors. It also protects the transformer from saturation since I recommend that the primary winding be coupled to the MOSFETs through a film capacitor.

It has occurred to me where I first saw this basic concept. Put on your reminiscing hat. It was a 1968--I think that is the year--edition of Electronics World. I am not quite as old as that would tend to indicate since I began amplifier design and electronics designing in general about ten years after that was published. An older hobbyist gave me a stack of the magazines.

The article was an early Class D audio amp. I was very intrigued by it. Almost needless to say, the idea can still be used in amplifier design. I can even see use for it for an analogue output stage.

Well, the idea is to let the lower transistor drive the upper one. Its collector connects to the base of the upper transistor directly. The emitter of the upper one connects to the collector of the lower one through a diode. The lower one keeps the upper one in conduction synchronization. It was done with bipolar transistors. I am not sure how far along in development MOSFETs were in 1968.

If you need more power without the loss through the diode, you can divide the task of the lower Bibolar transistor, IGBT, or MOSFET between two separate MOSFETs. The lower power stage MOSFET has its drain connected to the upper MOSFET's source while the driver MOSFET has its drain connected to the upper MOSFET's gate. Generally, the source of the upper MOSFET will be connected to its gate and the drain of the driver MOSFET by a diode.

Please don't try to take credit for the idea for yourself if you use it. I really like this concept. I bet someone could post a scan of the original 1968 diagram. Please do. That's all for now.

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PostPosted: Wed Jul 23, 2008 1:05 pm 
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Dog
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Location: Lisbon, Portugal
Interesting.
I would like to see that original article.
Electrone, do you have a schematic of your PSU, the almighty "flyback buster"?

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"Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius - and a lot of courage - to move in the opposite direction." Albert Einstein


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PostPosted: Fri Jul 25, 2008 12:15 am 
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Sheep

Joined: Sat Dec 23, 2006 8:27 pm
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Location: NAC
Hi Carlos

This simplest version maybe won't bother people too much concerning my particular schematic drafting style. I have a personal need for the overly tight appearance. I can accommodate questions about the theory of circuit operation but can't redraw the diagram.


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simple version flyback buster.gif


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