warpie
Well-known member
- Joined
- Feb 7, 2009
- Messages
- 1,591
Can somebody explain me why (let's say) for a -/+28VDC power supply, a 2x30V power transformer is recommended?
If my maths are correct a 2x30VAC would result in:
30 x 1.414 = 42.4
42.4 - 2V (diodes drop) =40.2V
So, the regulator's input would have to dissipate around 12V in order to output 28Vdc.
Even if we consider the Vo <= Vi +3Volts(min) requirement for a LM317 and also some mains sag, that's still a bit too high, no?
If my maths are correct a 2x30VAC would result in:
30 x 1.414 = 42.4
42.4 - 2V (diodes drop) =40.2V
So, the regulator's input would have to dissipate around 12V in order to output 28Vdc.
Even if we consider the Vo <= Vi +3Volts(min) requirement for a LM317 and also some mains sag, that's still a bit too high, no?
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