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How do I calculate power supply current after rectification?
How do I calculate power supply current after rectification?
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Old 2nd March 2012, 12:00 AM   #1
fingersoccer is offline fingersoccer  United States
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Question 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:
  1. How do I calculate the power supply's current after rectification?
  2. How do I calculate the current going to the preamp after regulation?
  3. How do I figure out the current requirements for the preamp?

Here's an image if that helps:
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Thanks, thanks, thanks!
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Old 2nd March 2012, 12:43 AM   #2
pdul is offline pdul  Denmark
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You forgot -1,2v drop in your rectifier bridge
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Old 2nd March 2012, 12:48 AM   #3
pdul is offline pdul  Denmark
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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.
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Old 2nd March 2012, 12:55 AM   #4
aardvarkash10 is offline aardvarkash10  New Zealand
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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...
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Old 2nd March 2012, 01:58 AM   #5
sawreyrw is offline sawreyrw  United States
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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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