Considering that classic power supply unit has too many weaknesse, for much better solution is used SWPSU(Switching Power Supply Unit). Its work method is far more complicated and requires more elements, but price is lower when it is produced in serial production.

Block sheme of Switching Power Supply Unit



Working principle is relativly simple and it is based on multi conversion of A.C. to D.C. and vice versa. Basic voltage is network voltage 220V/50Hz (somewhere 110V/60Hz depending on network standards in each country). Using gretz this is converted to D.C. and in point A (Ua) on filter capacity C1 we get voltage Ua=350 V D.C. (note again, this is for 220V/50Hz standard for network voltage). This voltage isn't acceptable for computer components which accept much minor voltages like +5.0 D.C. +12 -5 -12 +3,3. Taking down voltage from 350 D.C. to +5.0 V D.C. can be done in different ways. The worst part is to use serial of resistants. The efficiant one is to use transformer but transformerses inputs reques A.C. and input of transformer for D.C. is just a short circuit.

Thats why D.C. is artificialy converted to A.C., by CHOPPER (transistor T1). Frequency of chopping is 40 KHz so primar of transformer gets amplitudes of 350 V. Chopper is high voltage transistor T1 from series BUX(automobiles), BUY, BUZ

Tr. T1 works in active amplifing regime but it gets pretty hot so it needs to be mounted on specific cooler.
2 most warming components are switchig transistor (copper, T1) and tranformer because all energy flows through them. Transformers primar is collectors weight on T1 which is adverse because collector weight is individual and in momend of T1 braking (stoping of el. flow) and stopping of el. flow in transofrmers primar inverted self-produced reversed EMC (electro-magnetic current) is produced which tryes to overpolarize tranformer.

It is usual for transofmers to be dimenzioned for ther power that they transform and to other voltages with which they operate. This primarly worth for network transformers where operating frequency is 50Hz and core is made of so called tranformers sheets. On 40KHz transformers sheets wouldn't be good solution because of big losses, and thats why are for producing of these special transformers is used ferrite. Ferrite presents special mix of iron dust and synthetic rosin. Rosins do isolating every particle of iron dust, so electric admittance of ferrite is very small like at ordinary isolator. Magnetic preferences are very good even if weaker in comparation with transformers sheets. Because of high operating frequency core surface can be much minor unlike network transformers.