I am designing a 30w smps using transistors only in the oscillator circuit that generates the pwm and the switching transistors: which are the best option transistors to use

 

Nearly any small signal transistors will work. But why would you want to?

 

Ones that are available.

 

How high is Up ?
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Is this school work?

Also, please post your schematic. Paraphrasing Rear Admiral Joshua Painter,

"Engineers don't take a dump, son, without a schematic."

ak

 

Nearly any small signal transistors will work. But why would you want to?

As in, why would I want to what?

 

No one makes a PWM using transistors. We did 40 years ago. There are ICs that do the job.
I would use transistors like the 2N2222A. Years ago I used 2N3904 and 2N3907.

Sounds like a school project. Divide up the PWM into pieces and try to make each one. Can you make a simple oscillator? comparator? op-amp?

 

am designing a 30w smps

Let’s see, there s a bit if information missing here:

Input voltage? (constant or range?)
Output voltage? (constant or range?)
Output current? (constant or range?)
Buck, boost, or buck-boost?
Efficiency?