unknown power supply good enough?

Well i had my heart set on a 3 pound tor style transformer i had in the junk bin, but the voltages didnt work out so i found another traditional style transformer and wanted your opinion on it.

Its a ATS7164 that goes in pioneer vsxd506,vsxd466s, and vsx456 receivers. Its 8.5 pounds and semi shielded (has an extra iron sleeve wrapped around it). I measured 40vac plus center tap. So that should put me right on the mark for my lm3886. Thats what +-28vdc? My other main concern is I need another power supply rated for 24-30vdc and 100va. Would just 1 leg and the center tap fit the bill since its 8.5 pounds? I dont think i can combine a center tap like i can a dual secondaries setup.
 
You don't want to do that. It draws current on only one side of the winding, which leaves standing DC on the transformer. It'll saturate the core and you'll get excessive heating, buzzing, noise in the power, male pattern baldness, and all sorts of other horrible things.

Uh its only one coil. Wouldnt it just be like a auto transformer that uses multi taps along the same coil for buck boost?

Autotransformer - Wikipedia, the free encyclopedia



I could the problem with an unloaded side of a switch mode...
 
Wouldn't it just be like a auto transformer that uses multi taps along the same coil for buck boost?

The load you put on an autoformer should draw current through all 360 degrees of the waveform. You said you wanted DC, so I assume you're going to put a rectifier diode and some filter caps on the transformer. The rectifier only conducts for half the cycle.
 
Hi,
the centre tapped transformer can be used with a single bridge rectifier to create a dual polarity power supply.
The centre tap is taken to the junction between the two smoothing capacitors. This becomes the PSU Zero Volts.

You can tap off one polarity for auxiliary use. The total current drawn from that polarity must be within the current limit of the secondary.

If your 40Vac CT is off load measurement then it is probably 18-0-18Vac and expect +-25Vdc when on light load.

Now the second supply of 100VA @ 25Vdc will draw 4Adc. That is a lot of extra load for that half of the secondary!
 
I'd guess you want to build something like these schematics.

th_powersupply.png

http://i69.photobucket.com/albums/i43/Ty_Bower/MiscProjects/powersupply.png

The top is a full wave rectified supply. The bottom uses a bridge rectifier as Andrew described to give +/- rails.
 
Its amazing how a redrawing solves everything.

From that drawing it looks like i could draw full va from either side of the ground. So no rewire is needed. I just use the positive leg when i want to run the T amp, and it will get the whole transformers va, and i use both the negative and positive side of the ground when i want to use the lm3886, and i still will get the full va of the transformer.
 
.......... it looks like i could draw full va from either side of the ground. .................. and it will get the whole transformers va, and i use both the negative and positive side of the ground when i want to use the lm3886, and i still will get the full va of the transformer.
absolutely not!
Half the secondary is limited to the same current limit as the whole secondary.
When you use half you end up with half the VA.
 
Um maybe i worded it wrong.

lets over simplify and say 200va transformer.

So i can suck 200v full bridge at 1 amp, or 100v full wave at 2 amp. Both would be 200 watts. Thats how it works with dual secondaries.

I take it i cant use the same logic with a center tap? Am i limited to 200v at 1 amp or 100v at 1 amp due to the center tap leg limited to the same current as the outer legs?
 
lets over simplify and say 200va transformer.

So, can I draw 200v full bridge at 1 amp, or 100v full wave at 2 amp?

My apologies for rephrasing your question. I believe the peak currents through the secondary of the full wave rectifier will be roughly 1.414 times higher than if you used a bridge. I'll let one of the power supply experts verify my math.
 
According to hammond you are right.

http://www.hammondmfg.com/pdf/5c007.pdf

FULLWAVE BRIDGE Capacitor Input Load:
V (Peak) D.C. = 1.41 X Sec. V A.C.
V (Avg) D.C. = 0.90 X Sec. V A.C.
I D.C. = 0.62 X Sec. I A.C.

FULLWAVE Capacitor Input Load:
V (Peak) D.C. = 0.71 X Sec. V A.C.
V (Avg) D.C. = 0.45 X Sec. V A.C.
I D.C. = 1.00 X Sec. I A.C.


FULL WAVE BRIDGE Resistive Load:
V D.C. = 0.90 X Sec. V A.C.
I D.C. = 0.90 X Sec. I A.C.

FULLWAVE Resistive Load:
V D.C. = 0.45 X Sec. V A.C.
I D.C. = 1.27 X Sec. I A.C.

I think this will work fine. All i need is like 2.5amps at 25 volts to max out the tripath.