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I'm looking for equations on how to calculate output voltage of a simple power supply made of a step down transformer with Rs secondary resistance, a bridge rectifier and a capacitor with different loads.

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  • \$\begingroup\$ Do you know what RMS voltage is coming from the transformer? If so are you able to calculate the peak voltage coming from the transformer? If so then the DC voltage under light loads from the diode bridge is peak ac input minus about 1 or 2 volts (depending on the diodes). There will be ripple - do you know what your output cap and equivalent load resistance is? If yes you can calculate how much ripple you'll get. \$\endgroup\$ – Andy aka Jun 30 '13 at 16:33
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Here is a picture of what happens in order to help you find the rest of the formulas: -

enter image description here

It's easy to just let you have all the formulas but it's a learning process best undertaken with half-help. Call me mean if you will.

If Rs is a significant value (not usually that critical to simple power supplies) then you'll need to factor that is but if it's a small percentage of the DC load then ignore for now.

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  • \$\begingroup\$ Even there is a equation to calculate the ripple factor and ripple voltage too. It based on how much integrity that you need in this design. If you need it I could edit and this answer for you. \$\endgroup\$ – Standard Sandun Jun 30 '13 at 17:33
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The ripple is not a result of the load resistor but in fact is a result of the capacitor discharging into the load resistor which causes a smoother wave, the larger the capacitor the more negligible the ripple factor but it can be hazardous if too large a capacitor is used if you're looking to build an amplifier Here is an illustration, Im an electrical engineer and that is first years work

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