# Calculate power

Thread Starter

#### letoppina

Joined Dec 11, 2017
28
Hello,

considering a sinusoidal voltage source and a half-wave doubler rectification (as in the picture), how is it possible to calculate the DC power on a resistor R when considering ideal diodes?

Last edited:

#### Bordodynov

Joined May 20, 2015
2,814
• ScottWang
Thread Starter

#### letoppina

Joined Dec 11, 2017
28
Thank you very much for your reply. Could you please explain to me in detail the simulation?

#### Bordodynov

Joined May 20, 2015
2,814
I set the amplitude, frequency and capacitance of the capacitor as parameters. I did a parametric step-by-step analysis at various load resistances. I also calculated the average output voltage using the ".measure" command. And lastly, I empirically selected a formula for the output voltage. To calculate, I defined this formula in calculating the voltage in node "M" with the help of a dependent voltage source. I took the diode model close to the ideal diode (this is only available in LTspice). I compared the average value of the output voltage with the values obtained by me from the empirical formula by finding the ratio of values. I got the numbers close enough to one.

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Thread Starter

#### letoppina

Joined Dec 11, 2017
28
Ok, thank you for the explanation. I still have a couple of questions: why do you have to compare the value of the output voltage with the value of voltage in the node M? How did you obtain the empirical formula of the voltage M?

#### Bordodynov

Joined May 20, 2015
2,814
Thread Starter

#### letoppina

Joined Dec 11, 2017
28
Thank you again for your answer. However, what I meant was: do you have a reference that explains how you obtained the empirical formula in the voltage source M?

#### Bordodynov

Joined May 20, 2015
2,814
No. I have no reference to my formula. It just seemed like a formula like that would be true to me. So I took advantage of my intuition. But you can make equations (if your knowledge allows you) and get your formula.

Thread Starter

#### letoppina

Joined Dec 11, 2017
28

#### Bordodynov

Joined May 20, 2015
2,814
Thread Starter

#### letoppina

Joined Dec 11, 2017
28
Yes, I mean, where did you take this value from?

#### djsfantasi

Joined Apr 11, 2010
7,586
Yes, I mean, where did you take this value from?
It’s not “taken” from anywhere. It is a mathematic constant. “Ln()” is the natural log function. “2” is, well, 2! The integer after 1.

Thread Starter

#### letoppina

Joined Dec 11, 2017
28
I think there is a BIG misunderstanding here. What I meant was, how did the natural log function popped-up in that formula? Could you please give me a scientific explanation of how you arrived to the formula (A*RL/(RL+1/(ln(2)*f*C))*2? And "would be true to me" is definitely not an acceptable answer in a scientific context.

#### Bordodynov

Joined May 20, 2015
2,814
I received the answer intuitively (I have already written about it).
Although I can make a discrete equation and solve it (I really have to work hard), but I don't want to do it. It is very tiring. I understand that this is homework. Who else needs to solve an ideal problem with perfect elements (diode)? And if such a task has been given, then it is assumed that the theoretical basis has been given to you, and it is assumed that you will do it yourself. I used to get involved in the learning process, and I was beaten for it. I even asked to be disconnected from seeing the homework and did it, for which I am grateful.

• Danko