transformer
I want to make transformer which can convert 220 volt ac to 20-0-20 volt Ac(Step Down) 6 Ampere for audio Amplifier. Now I have a question that For 6 Amp Calculation I should consider 3-0-3 Ampere for or 6 amp on both winding of Secondary or Whole Secondary winding with 6 Amp .
20-0-20 Whole winding 6 amp or I can use 3 amp winding for 0 to 20 and again 3 amp winding for 0 to 20 (20-0-20)
Since you mentioned transformers and \$12\$V adapters, I assume you are stuck in the old ways of linear power supplies, which typically only have a power efficiency of between \$50\$%-\$60\$%
So if you go from \$120\$V AC at the wall to \$12\$VDC to \$5\$VDC there is a \$50\$% worst case power conversion loss at each stage. It won't matter if you step up or step down, you can assume that the up-conversion or down-conversion is equally efficient, and the losses are more from the linear regulators than anything else.
In this day and age, you should really only be using switching power supplies, especially for digital electronics like a tablet. There are numerous designs available and numerous chipsets with efficiencies approaching \$98\$% these days.
If you go the switching regulator route, then the path will be \$120\$VAC -> \$12\$VDC -> \$5\$VDC and you can expect \$80\$%-\$90\$% efficiencies at each stage. This is the path I would use if you were coming from the wall, because this is two buck regulators in series and a buck regulator is inherently more efficient than a boost regulator. This is because a buck regulator is either on or off, and in the on cycle it is delivering current to the load, and in the off cycle the inductor is doing it. However, a boost regulator first must deliver current to ground through the inductor to build up the inductor's magnetic field, then in the off cycle (and during the collapsing field) the inductor delivers current to the load. So the resistive losses of the inductor during the buildup phase of a boost regulator are wasteful (however, modern boost controllers go through extra hoops to minimize this wasted energy)
However, if you are working off a battery source (you did say "tablet", so I assume portable), then your choice of buck vs boost is often directed by your source voltage available. If your source is a couple of lithium-polymer cells, then you only have a few volts to start with, and so you will need a battery -> boost \$5\$V -> boost \$12\$V configuration.
Assumed facts : Single phase low voltage electrical utility.
Needs : Has single phase input, 3 phase AC motor controller and 3 phase motor on hand. Can transformer be used to step up voltage.
If you have a single phase transformer (5 KVA) which is rated as step up (or step down) rated for 120 VAC to 240 VAC (or vica versa), can you use said transformer?
Yes, and not much concern for inrush. Part of the fun and learning is just going ahead and trying it. Just be careful. The KVA size could be a problem with inrush current in a home environment (circuit breakers). Use prudence and stand back. You should be ok. Doesn't matter if it is toroidal or not in your application.
Best Answer
When a center tapped transformer is labelled with a particular current rating for its secondary, the number actually stands for the capability of the current carrying capacity of the copper wire in the secondary.
This means the each side of the transformer output is capable of delivering the labelled current.
In case of 20-0-20, 6A, if two outer ends of the transformer winding is connected to a bridge rectifier and the center tap is not used and no filter caps are installed, you will have 40 volt @ 6A (RMS).
If you use only one outer end and the center tap and connect it as above, you will have 20 volt @ 6 A (RMS).