# Power supply calculations by vead

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#### bertus

Joined Apr 5, 2008
22,231
Hello,

I got this in an email from you:

i want to build regulated power supply circuit that has input voltage 230v ac
and output voltage 12dc 20ohms load i know i need transformer, diode,capactior,
and other component but iam not surge what rating
how to find out right value of component and calcuations
As I do NOT reply on emails, I post your question here.
This way the others can reply too.

If you search this forum, you will find a lot of examples.

Bertus

• Joined Nov 24, 2011
629
sir i want buil power supply circuit with help of fomula but i can not deside what is the right value of componet for example
what is voltage rating of transformer, diode and other component plz help

#### RRITESH KAKKAR

Joined Jun 29, 2010
2,829
sir i want build power supply circuit with help of formula but i can not decide what is the right value of component for example
what is voltage rating of transformer, diode and other component plz help
Wasting time in mails and PM you can get solution by searching for Rectifiers......

OK, as you want to convert AC in DC for this the device is called rectifier..
they are of two types:-
1. Switching regulators ( difficult to build)
2. Linear regulators ( easy to build)

step to members will building...
1.voltage rating you need at output side...??
2. current rating...??

If you want a 12V DC and .8mA supply probably...
so, buy a transformer of 12-0 or 12-0-12V of 500mA.
diode 1N4007 which can supply 1A max. at peak reverse voltage of 1,000V.
and a capacitor depends on load rating.
you take it of 22,00uF will work perfect, voltage rating of C should be higher than 20V (at least)

here are some schematic you should try first then use a regulators.

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• Joined Nov 24, 2011
629
but i want design schematic first and build prectical so i need formula to calculations for component rating
- how can find working voltage of diode transformer capactior-
if i know i/p 230vac o/p 12vdc and 20ohms load

#### RRITESH KAKKAR

Joined Jun 29, 2010
2,829
The ideal principle of transformer:-
Power input = Power output
So, Power = V*I or V^2/R or I^2*R

we will use V*I

Vi/p*Ii/p = Vo/p*Io/p
as Vi/p = 220V
let Vo/p = 12V
we require Io/p = 500mA
so, 220/12=500mA/Ii/p

we get input current Ii/p = 27mA
we don't want to go in these equation will designing....
For finding the value of filter capacitor you need to know load current and ripple voltage, i would say no need to go in this right now....

if i know i/p 230vac o/p 12vdc and 20ohms load
The current on 20ohm will depent on rating of transformer and diode....
so if you will connect this 20ohms load to different rectifiers the load current would not be same.

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• Joined Nov 24, 2011
629
if i design circuit transformer+rectifier+capactior+regulatior+load then how can i find total resistance of circuit what concept i learn to need

#### RRITESH KAKKAR

Joined Jun 29, 2010
2,829
Why you want to calculate the resistance of circuit..........??
this is no like hybrid parameter of transistor, take it easy first learn basic they move to comple part.....

• #### R!f@@

Joined Apr 2, 2009
9,890
Pritesh, u r getting to be quite good at this..eh!.

I guess we'll leave this thread to u to complete. but we will be watching to see if you might need assistance.

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