SMPS DESIGN USING UC384X SERIES

SMPS design is always a difficult task for most beginners even to many intermediate engineers based on the fact that the principle and the rules looks tedious. Flyback approach is always a very good concept when you needed a current not above KW but you can still use flyback approach to achieve a higher power rating if you can interconnect them together or follow some set rules.

While I was getting my hands dirty, experimenting smps flyback approach I burnt a lot of IC and power transistors and other components before i was able to understand the principle revolving around it. SMPS design both buck converter, boost converter, buck-boost converter, push-pull, half-bridge and full bridge are not a difficult task but they need a very huge attention else nothing will work and debt may set in. Will be pointing out some rudiment behind SMPS design. Namely on buck converter using flyback approach:

* TRANSFORMER SELECTION: Flyback uses a gapped ferrite core or gapped core, the core can be gapped between the Core or just one of the core providing the gap, in summary any core without gap cannot work for flyback converter

* MOSFET SELECTION: For a design mainly AC-DC a very high voltage rating mosfet should be used with very low Rds, also sufficient current should be put in place. Mosfet like IRF840, 740, 11N60, 20N80, 10N60 a mosfet with a fast switching ability should be used.

* COPPER SELECTION: The thicker the coil the more skin effect you are putting to the core, the core must be of a low thickness but can be combine in parallel to get higher current. Every copper cable as a maximum frequency so endeavor to check the frequency before using the copper and also check the maximum current you can get from the copper before use.

*UC384X Series: The UC38X family comes in different form which is a current mode Single PWM Driver, the 42/43 have same frequency output while the 44/45 divide by 2.The 42/44 is a high voltage from 10v to 16v with a startup voltage from 16v to 35v though it as an internal zener, but the 43/45 are meant for low voltage applications 7.6v to 8.6v startup but are mainly used for buck converter and boost-converter where input is not that high. They all have a very low startup current ability around 5mA before the auxiliary power supply is given.

*WINDING DIRECTION: The winding of the transformer is another point to note else nothing will work and it can also result to the damage of the entire circuit. Over voltage can damage the IC through auxiliary winding and under winding can make the IC to start sourcing for excessive current which can damage the IC and consequently the entire design. NOTE: When winding the ferrite core a gapped core should be used have stated that above and same direction should be follow throughout the entire winding, the primary winding should be overlap on the secondary in full detail the primary half winding should be wound first then follow by the secondary and then follow by the half of the other primary left, lastly wind the auxiliary turn.

Below are some of the SMPS FLYBACK converter I designed