Re: Switching Regulator for Audio Amplifier

On Sep 21, 3:55 pm, JosephKK <quiettechb...@xxxxxxxxx> wrote:
On Sun, 14 Sep 2008 12:16:03 -0700 (PDT), Fred



<frederick.br...@xxxxxxxxx> wrote:
On Sep 14, 12:59 pm, Eeyore <rabbitsfriendsandrelati...@xxxxxxxxxxx>
wrote:
Fred wrote:
In any case, I guess I'll buy a 115 to 2 x (50 @ 5A ) 4% transformer
and give this another shot.

That should give me 38.4 out of the transformer with a 120 at the
mains.

BEWARE. Transformers may or may not be rated loaded. When rated loaded it will invariably be with a
RESISTIVE load, not a rectifier and capacitor inpur PSU.

Ask for the *turns ratio*. That's the only way to find the 'no-load' DC voltage.

Graham

Hey Graham,

Let me see if I can address these in order:

I did the thermal calculations. I used a 3C/W heat sink, and directed
a 40mmx40mm fan at during testing because it got hot when at full
load.

The 0.1uf and the 470uf were local bypass close as possible to the
pins of the device. In the gain clones, its those caps, a bridge, and
the tranny. Absolutely minimalistic.

My uinderstanding of transformer ratings is that the regulation is
drived from the voltage rise from load to no-load, and they deliver
the stated VA when resistively loaded.

I'm unsure about what difference a bridge and cap filters would do to
the output of the PS besides lower the VA a bit due to the diode drop
and the caps ESR

Fred.

Check out the diode conduction angles in the fully loaded case,
lighter loads just reduce the conduction angle. This will also
provide ripple data.

Now that I got the thing working better. The no-load voltage is 73.3V
across both rails, and 68.1V under full load.

They do get a bit warm though. I ran spice simulation of five
different transformers:

The current one, 384VA 10% reg 115:2x24

225VA 7% reg 115:2x24
300VA 6% reg 115:2x24
400VA 5% reg 115:2x24
500VA 4% reg 115:2x24

These four are based on Plitron products.

Interesting resuls were that the 300VA produced the least THD by a
small amount, and the 384VA transformer required the most input
power. I suppose that has to do with regulation and efficiency.

Diode conduction for all the simulations ran between 25 and 35
percent. I have to put the amp back on the bench to test what it
actually is. I been listening to it. The distortion is so low that
even when its loud it sounds quieter than it is because I'm used to
hearing distortion at that level. An interesting subject thing.

Fred
.

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