How do I calculate power supply current after rectification? - diyAudio
 How do I calculate power supply current after rectification?
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 1st March 2012, 11:00 PM #1 diyAudio Member   Join Date: Feb 2010 Location: Austin, TX How do I calculate power supply current after rectification? So I have a power supply I'm using to power a chip amp. The transformer is rated at 250VA with 24V secondaries. I calculated the rails voltage after rectification with this equation: Er = √PR(1.4) + 4 (or, more simply, 24V * 1.4), which comes out to around 33.6V. I would like to knock the voltage down to 15V to use with a preamp, probably with a switching regulator since I understand they're more efficient than a linear regulator. I need to understand a few things before I can do this: How do I calculate the power supply's current after rectification? How do I calculate the current going to the preamp after regulation? How do I figure out the current requirements for the preamp? Here's an image if that helps: Thanks, thanks, thanks!
 1st March 2012, 11:43 PM #2 diyAudio Member   Join Date: Jan 2009 Location: Copenhagen You forgot -1,2v drop in your rectifier bridge
 1st March 2012, 11:48 PM #3 diyAudio Member   Join Date: Jan 2009 Location: Copenhagen The most simple would be to use LM317/337 as regulators for your preamp. you can draw up to 1,5 amp from those, more than enough for most preamps.
 1st March 2012, 11:55 PM #4 diyAudio Member     Join Date: Mar 2007 Location: Auckland, NZ PSUDII will help with the basics. The current requirements of your regulator are specific to its circuit, as are the current requirements of your pre-amp - gotta know those first... __________________ "It may not be easy for some to not hear differences, even if they are not there." - Vacuphile,
 2nd March 2012, 12:58 AM #5 diyAudio Member   Join Date: Apr 2006 Location: Minnesota You need to work backwards. Determine the output power of the amp and preamp. Then determine the power required at their inputs. This is not a simple task. Now keep going until you finally determine the total input power.

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