Constructing a variable power supply

[spybot]

I want to build a variable power supply which can provide upto 25V. There seem to be many possible options around, I dont know how to compare these in terms of efficiency
I'd like some advice on this and other possible designs
Thankyou

 

[svhb]

high efficiency = SMPS
low efficiency = linear regulator but big heat sink needed
low current = linear regulator (and simple design)

So what is the current the power supply must deliver?

 

[Tahmid]

Hi,
Like you said, there are many possible options. To have something between an efficient design and simplicity at reasonable current outputs, I would say you could use a step down transformer and use a switching regulator. For switching regulator, check L4971, L4964, L4970, L496x, L497x. Transformer should be easy to acquire.
The easiest solution, however is, use a step down transformer and linear regulator.
The most efficient and complex solution is complete SMPS. Use a controller like UC384x, SG3525, TL494, etc. Use these to drive MOSFET(s)/IGBT(s) in either flyback, forward, half-bridge, full-bridge configuration as required (depending on power requiremnt).

Hope this helps.
Tahmid.