Hi,
We are designing a dc-dc conversion circuit using fixed voltage regulator lm140k.
Input voltage is 28V and output required is 12V.
Datasheet specifies an application circuit for high voltage using a NPN transistor cirucuit as shown
Is it mandatory for a 28V input as absolute maximum rating specifies 35V.
Our load current requirement is 250mA @ 12V continuous.
In case a transistor to be used, we need to go for Power transistor with 2W dissipation. We need a derated transistor Pd, as our operating temperatures reach 70deg, and it is difficult to get Transistor with 2W derated power dissipation at 70deg.
Kindly let us know if a input transistor is really required for a 28V input.
Regards,
Phaniendra Kundeti
