Dear fenris,
I have reviewed some information about tota C/W of the component so I forgot to mention to you that you will also have to add the thermal risistance of a compnent when attahced to a heat sink it is about 1 C/W as an average, and it goes alittle down according to the way the component is attached to the heat sink that is to say directly , through a mika , through a thermal contact greese ..etc. but i have read that the most one is 1 C/W so t
I had to check also the formula thermal resistance of a heat sink is equal to 50/Square root of the total heat sink space (in Square centimeteres not enches and not millimeters )

 

Transistors need a lot more base current than their hFE for them to saturate properly.
The datasheets show them saturated well with a base current that is 1/10th the collector current.

A darlington transistor like a TIP120 has a minimum current gain of 1000 but has its saturation voltage spec'd when its base current is 1/250th the collector current.

 

dear fenris,
I have found ics that are called Darlington arrays tehy control loads from 1.5 A to 4 A with great voltage response some 50 V some are for 80 V maximum rating it is much easier to start these switches than worry which is the best two compatible transistors that best fit your application because those babies can be triggered with only 25 mA only to switch on what do you things each IC contains at least 4 switches of Darlington type what do you think guys?