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-   -   How do I calculate power supply current after rectification? (http://www.diyaudio.com/forums/power-supplies/207920-how-do-i-calculate-power-supply-current-after-rectification.html)

 fingersoccer 1st March 2012 11:00 PM

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:
http://i41.tinypic.com/dmclg1.png

Thanks, thanks, thanks!

 pdul 1st March 2012 11:43 PM

You forgot -1,2v drop in your rectifier bridge

 pdul 1st March 2012 11:48 PM

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.

 aardvarkash10 1st March 2012 11:55 PM

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...

 sawreyrw 2nd March 2012 12:58 AM

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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