# How To Make Dc Power Supply ?

Discussion in 'General Electronics Chat' started by abhimanyu143, Aug 29, 2014.

1. ### abhimanyu143 Thread Starter Member

Aug 25, 2014
211
1
component
transformer
diode rectifier
filter capacitor

1. transformer
primary voltage Vp= 230 Vrms ac
secondary voltage Vs= ?
primary turns Ns = 5
secondary turns Np= 1
primary current Ip =?
secondary current Is ?
formula for transformer
Vp/Vs=Ip/Is=Np/Ns

secondary voltage

Vp/Vs= Np/NS

230/Vs=5/1

Vs = 46V rms Ac

secondary current

Is= 46/50= 0.92 amp rms Ac

primary current

Vp/Vs=Is/Ip
230/46=0.92/Ip

Ip= 0.184 amp rms AC

primary voltage Vp= 230 RMS ac
secondary voltage Vs= 46 volt Rms Ac
primary turns Ns = 5
secondary turns Np= 1
primary current Ip = 0.184 A rms Ac
secondary current Is = 0.92 A rms Ac

2.rectifier
If we connect single rectifier diode then

We know following for rectifier

Input voltage = 46 Vrms Ac

Input current =0.92 Arms Ac

I have to find out output voltage, current for rectifier

Output current for rectifier

Idc= Vs/RL= (46-0.7)/50=0.906 dc

Output voltage

Vdc = Idc* Rload=0.906*50= 45.3 vdc

3.filter capacitor
now we know input voltage and current for capacitor
Idc= 0.906 dc
Vdc =45.3 vdc

I want to do some calculation for capacitance
how to choose capacitor value ?

Last edited: Aug 29, 2014
2. ### #12 Expert

Nov 30, 2010
18,076
9,684
Sqrt2 C Er F = I where Er is the allowable, peak to peak ripple voltage, F is the frequency after whichever rectifier design you used, C = capacitance, and I = current to the load.

Jul 18, 2013
18,208
5,587
Voltage out 46vac x 1.414 = 65vdc.
Max.

4. ### abhimanyu143 Thread Starter Member

Aug 25, 2014
211
1
I know only frequency 60 Hz and load current Idc= 0.906 dc
how to determine peak to peak ripple voltage ?

5. ### abhimanyu143 Thread Starter Member

Aug 25, 2014
211
1
I don't know what are you telling ?

6. ### #12 Expert

Nov 30, 2010
18,076
9,684
Use the math I gave you. sqrt2 = 1.414 60 Hz = F if you didn't use a full wave rectifier. It's 120 Hz if you did. Either you decide the ripple voltage you want to allow or you decide the capacitor size. The answer comes out of using the formula.

7. ### #12 Expert

Nov 30, 2010
18,076
9,684
He is telling you that the RMS voltage of a sine wave will reach a DC peak of 1.414 times the RMS value after it is rectified (minus the voltage lost in the diodes).

8. ### MikeML AAC Fanatic!

Oct 2, 2009
5,444
1,074
The first figure might help you understand the peak voltage that the filter capacitor charges to, and how the value of the filter capacitor effects the ripple. The second figure shows why it is better to use a full-wave rectifier...

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• ###### 199a.jpg
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Last edited: Aug 29, 2014

Jul 18, 2013
18,208
5,587
...And if you want 46vdc as a final result, that would be 46vdc X 0.707 = 35vac required.
Max.

10. ### cl10Greg Active Member

Jan 28, 2010
52
0
I am not sure how set in your design you are, but have you looked at any of the various power supply designer web tools? TI has one, Fairchild, Power integrations, etc...

11. ### ISB123 Well-Known Member

May 21, 2014
1,235
546
Use 4700uF cap at 80V.

12. ### abhimanyu143 Thread Starter Member

Aug 25, 2014
211
1
primary voltage Vp = 230 v ac
peak voltage of secondary=65.004 V Ac
Rms voltage of secondary = 46 V ac
output of rectifier = 65.044-0.7=64.344 V ac
main frequency F= 60 Hz
peak to peak ripple voltage Vr= 2 v

using formula for capacitance

C=0.906/2*60*2
C=0.906/240

C=0.003775 F

13. ### abhimanyu143 Thread Starter Member

Aug 25, 2014
211
1
If my capacitance value is correct then I want to add regulator Ic
how to do some calculation for regulator Ic ?

Last edited: Aug 30, 2014
14. ### #12 Expert

Nov 30, 2010
18,076
9,684
C = Iload /1.414 * F *2
C = .906/1.414 * F * 2
C = 53388 uf

Read the datasheet for the regulator you want. It tells all about which capacitors to use and how to adjust for different output voltages. They are often a little different from brand to brand, so pick one and read about it. Small capacitors are used to keep the regulators from oscillating. Your big capacitor is finished.

abhimanyu143 likes this.
15. ### abhimanyu143 Thread Starter Member

Aug 25, 2014
211
1
what is 1.414 ? C=I load /2*F*Vr Is it wrong ?
If I connect regulator I think I need 2 small capacitor

16. ### ISB123 Well-Known Member

May 21, 2014
1,235
546
Last edited: Aug 30, 2014

Apr 5, 2008
19,549
3,984
Hello,

Have a look at the attached PDF.

Bertus

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18. ### #12 Expert

Nov 30, 2010
18,076
9,684
On page 8, that PDF goes right into talking about Vpeak, but I can't find where it explains that Vpeak = the square root of 2 times the RMS value of the voltage. Transformers are usually labeled in RMS voltages. ps, the square root of 2 is 1.4142136 according to my calculator.