power suply with out transformer

[dewingong]

To all,
Can some body help me with a schematic diagram for a power supply unit for a lap top wit out using a step down transformer : input 100 - 260v ac , output 19.5v dc.
Thanks.

 

[FvM]

Safe isolation is absolutely necessary in this case. In most cases, it's achieved by off-mains SMPS with an isolating flyback transformer. That's far from an easy design, not suitable for a DIY project.

If you are interested in the circuit concepts, you'll find a lot of reference designs from the manufacturers of SMPS control IC and power transistors. Many application circuits have been published e. g. by Unitrode, absorbed by TI some time ago.