General opinion requested for topology

[ITPhoenix]

I have been on the Fairchild site using some of their design tools. But the problem is there is no way to get a 250w QRSMPS, as far as I can see. For a hybrid guitar amp, here's the specs.

AC in: 85-275VAC 50-60Hz

DC outs: 380v 30mA for the tubes, 6.3v 2.8a for the heaters, +--35v 7A for the two SS amps.

So the question is, what topology is best for something like this? I started with the Fairchild (integrated FET) FSCQ series, but they discontinued the "big one".

I would prefer to use some kind of design tool because I am not not that sharp to go scratch; however, I can read, punch in the numbers, wind, and build the board.

Any ideas or pointers would be appreciated.

 

[MicrosiM]

I can recommend forward topology or half bridge

 

[ITPhoenix]

Thanks. However, Philips does not recommend half bridge for under 500w for the following reasons:

The need for two 50/60 Hz input capacitors is a drawback
because of their large size. The top transistor must also
have isolated drive, since the gate / base is at a floating
potential. Furthermore, if snubbers are used across the
power transistors, great care must be taken in their design,
since the symmetrical action means that they will interact
with one another. The circuit cost and complexity have
clearly increased, and this must be weighed up against the
advantages gained. In many cases, this normally excludes
the use of the half-bridge at output power levels below 500W.

Power Semiconductor Applications
Philips Semiconductors

I will look into the forward, or recalculate my loads which may be closer to 200w for the flyback, I may be able to reduce the loads to some extent as well. I know 380v for the tubes is not essential, but other component values will have to be adjusted. The Fairchild flyback calculator will go to 12A on the switching device (I lim) before it starts failing to produce results. I just have to use a controller with an external MOSFET. I found the ST L6565 which is regularly used in CRT apps. I am looking around for a piece of plexiglass now.

 

[ITPhoenix]

You are correct. That was an old commentary. NXP has the new TEA1713 or TEA1716 good for at least 500w and is half-bridge. It also runs at higher average freqencies, so the transformer is smaller with less windings. It is feasible to wind by hand! The design tool is also much better than Fairchild's.

The tool is limited to two outputs, but it seems possible to squeeze in a couple more low power outputs, as long as the designed wattage is not exceeded. e.g., +/- rails for control electronics, or 6.3v for a few tubes.

There is also the mandatory addition of two torroids for the built in PFC. Not a big deal.

Thank you for your correct counsel.