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Old 29th November 2005, 06:07 AM   #11
mflorin is offline mflorin  Romania
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It will be nice if you post converter's key data.
As far as I understood, you need -35V / 0 / +35V at 2.5A, so your output power is around 175W. For this power level and selected input voltage range (10Vmin - 15Vmax), the primary current has a pick value of 82A at 10V input and assuming 70% efficiency. I'm affraid that flyback is not suitable for this application. I suggest a push-pull topology.

Can you post a schematic?
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Old 29th November 2005, 08:15 AM   #12
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I hate measured amps my shorting the outputs with the amp meter and on the 2A setting it went to the bottom = more than 2A, it also gives 20.3V unloaded, if i turn the bass and volume up on the amp it only drops to 19v. This may sound impossible but its true!!

Btw according to the smps calculation site it will be 25A input with a flyback config for 35v 2.5A out.

Heres the schematic of my first ever prototype:
Click the image to open in full size.
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Old 29th November 2005, 02:51 PM   #13
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Now i have made a new transformer from the core off a tv flyback transformer and it works mutch better. i accedently hit 60v per rail because i forgot to turn the vfb pot down to minimum.

This took out the diodes i used and destroyed a cap, and it may have hurt a component on the amp because everything over 20v makes it sound like a mad cat and oscillating @ 1hz. Now the thing has some power and capability of destroying components if you dont pay attention
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Old 29th November 2005, 07:41 PM   #14
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There was nothing wrong with the amp, it was the emi filters that were made for mutch lower switch freqs.
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Old 30th November 2005, 04:43 AM   #15
mflorin is offline mflorin  Romania
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Yes it is true that for 35V/2.5A at the output, the primary peak current is around 28 for unity efficiency.
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Old 2nd December 2005, 09:36 AM   #16
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Now i have built a third prototype that works very well, only issue is that when i start to reach 35v and above the amp starts sounding like *FFFFFFFFF* Why i dont know. Also the amp has the issue taking so mutch amperage in the start that i have to turn the smps vfb pot down otherwise my 12v 8A ps gets overloaded so the smps controller looses power and shuts down.

With the smps the amp also has alittle crisp treble, on some freqs the treble sounds alittle like a broken tweeter, but good bass.

Some pics:
Click the image to open in full size.

I have changed the board alittle since i had done an error there after i took the pic:
Click the image to open in full size.

A transformer from a 200W pc ps rewound:
Click the image to open in full size.

And finally the schematic:
Click the image to open in full size.
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Old 2nd December 2005, 10:23 AM   #17
Kenshin is offline Kenshin  China
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Low input voltage means MOSFET with BVDSS>3VCC available, class E resonant topology may be used -- extreme efficiency & clean waveform.
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Ideal OP doesn't make perfact linars but make perfact switchers.
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Old 2nd December 2005, 11:46 AM   #18
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That sounds interesting, what is it ?

Now im making a new transformer that should work better than the one im using now that actually is from a pushpull topology ps, the new one is from a 200w flyback atx ps.
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Old 6th December 2005, 05:51 PM   #19
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Now i have settled for the board from the second prototype and have descided to finalize it together with the bobbinless core from the flyback trasf as a finished product smps.

Gonna do some final tests and adjustments and then box it and call it finished.
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Old 7th December 2005, 04:53 PM   #20
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I have came up with a problem that i dunno what do do.

If i don't turn the vfb pot all way to zero the smps just shorts out the 12v source i use. What is causing this and what options do i have to solve it ?

Anyone having any ideas ?

This problem is preventing me from putting the smps in a box.
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