basic questions on DC......

[p72]

What DC Voltage should I get after the bridge rectifier if my Input is 110/220V ac, 50/60Hz? (Bridge rectifier is made of four 1N4004 diodes). Is there a formula to calculate the same?
How can I step down output voltage that I get from rectifier (except converter)? I am looking for 24V dc as a final output voltage.

Thank you,
p72

P.S. I have posted same on other thread by mistake.

 

[KerimF]

If no load and a small filter capacitor at the output of the rectifier, the DC voltage is about:
Vrms * SQRT(2)

 

[p72]

Hi KerimF,
Thanks for the quick response.
I did not get your point. Could you please explain in detail?

 

[KerimF]

As you know 110V or 220V are actually RMS values for sinusoidal voltages (AC).
This means if we have a resistive lamp and we connect it to a 110Vac sources then to 110Vdc source, its power dissipation will be the same.

If there is no load and no filter capacitor at the output (DC side) of the full-wave rectifier (4 diodes), we get at its output the same Vrms of its input (if we neglect the small voltage drop of the 2 diodes). But the two cycles between its DC terminals will be of the same polarity (hence the word rectifier).

Also in this case (no load and no filter capacitor), we can compute the average (DC) voltage at the output and we get the approximated value:
Vdc = Vrms * 0.9
If Vrms = 110V , Vdc = 99V
If Vrms = 220V , Vdc = 198V

Obviously, you can measure this DC voltage using a DC voltage meter.

By adding just a small capacitor (but rated for high voltage as 400V), the capacitor is charged up to the peak of the sinusoidal voltage:
Vpeak = Vrms *SQRT(2)
If Vrms = 110V , Vpeak = 155.5V
If Vrms = 220V , Vpeak = 311V

Also, you can measure this high DC voltage using a DC voltage meter.

 

[p72]

Thank you KerimF.
Can you point some book/paper/article for the same? (That describes all design parameters.)

 

[KerimF]

In my opinion, to learn the basics, one should have in mind a specific goal to achieve starting from simple projects but preferably also useful in a way or another. And while he solves it, step by step, he likely discovers new questions that sooner or later he will also find their answers till the project is practically completed (though not necessarily be perfect). And from one project to another, he will find out that he is getting old (as I am) and still need to learn

Now when I forget about a specific formula or certain topology, I just spend a few minutes and sometimes hours searching for it on the internet. In the past, we had books only, and where I live it wasn’t easy for me to get the good ones.

Anyway, don’t lose hope, you can always ask ‘specific’ questions that are most interesting for you in each period of time, and you will surely find someone to give you a detailed answer directly or via a reference.

 

[p72]

Just wanted to make sure basics for myself.