D.C power supplies, regulated linear power supply question

Design giving the necessary ratings and characteristics the necessary for the transformer, bridge rectifier capacitor and regulator , a 12v , 2A regulated power supply .

the available mains supply is 230v+10% @50hz

so far I have :

Regulator - Standard voltage regulator will require 2v to be maintained across it to prevent drop out , therefore input voltage should not drop below 14v

Transformer - Va atleast 50% & volt drop = 24v

Capacitor - the minimum peak voltage to the regulator input

(24-10%) x 1.414 - 2 = 28.8v

maximum peak voltage

(24+10%+10%)x1.414-1.4 = 38.9v

The minimum peak full hand voltage defines the minimum of ripple voltage (28.8-14) = 14.8

suitable reservoir capacitor ?

I am uncertain if these figures are even correct , I think I am close but could do with some guidance

thank you

• You left out the all-important value of the capacitance on the output of the full wave rectifier. You pick the tradeoff between the capacitance and voltage dip, then work from there to find the other specs. Of course if any of them turn out too onerous, you go back and adjust your initial values. Note also that this type of regulator will make a lot of heat, which you have to consider how to deal with. – Olin Lathrop May 21 '15 at 16:38
• I would use a transformer with a much lower secondary voltage than you are. That is a lot of extra power to dump using a linear regulator. – R Drast May 21 '15 at 16:42
• C = 2A / 50Hz * 1V whence C = 2/50 Farads = 10,000 uF is that what I am missing ? – Chris May 21 '15 at 16:45
• so if I went for a 18v that would be a better option ? – Chris May 21 '15 at 16:52