# 12 volt dc power supply

Discussion in 'The Projects Forum' started by dane, Jan 31, 2009.

1. ### dane Thread Starter New Member

Jan 31, 2009
3
0
am building a 12 volt dc power supply with the following specifications:

output power- 1 watt

output voltage- 12volt

output current- 1amp

ripple factor- <1%

i need the formulas to calculate capacitance, diode, transformers and other components. i didnt get any values for the components thats why i need the formulas. plz help

thank you!

Apr 5, 2008
19,168
3,836
Hello,

Your caculation for the power is wrong.
A 12 Volts power supply that can deliver 1 A has a power of 12 Volts X 1 Ampere = 12 Watts.

Here is a simple power supply schematic from bill bowdens webpage with a LM 317.
It is capable of 1.5 Ampere.
http://ourworld.compuserve.com/homepages/Bill_Bowden/page12.htm

Greetings,
Bertus

3. ### dane Thread Starter New Member

Jan 31, 2009
3
0
that site is no help. sorry about that yes it it is 12 watts

4. ### mik3 Senior Member

Feb 4, 2008
4,846
69
Is this a school assignment or a personal project?
If it is a personal project you can use a LM7812 to regulate the output voltage.

Apr 5, 2008
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6. ### dane Thread Starter New Member

Jan 31, 2009
3
0
yes it is a school assignment

7. ### mik3 Senior Member

Feb 4, 2008
4,846
69
These equations were derived by assuming the ripple voltage as a triangular wave and give approximations of the actual values.

Vr=Idc/(2*f*C)

Vr=ripple voltage peak-peak
f=supply frequency
C=filter capacitance

k=Vrms/Vdc

k=ripple factor
Vrms=Vr/(2*sqrt3) rms ripple voltage

Vdc=1/{1+1/[4*f*C*R]}

C=filter capacitance
f=supply frequency