# Need help with a diode circuit problem

Discussion in 'Homework Help' started by copper_pipe, Sep 30, 2014.

Sep 30, 2014
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2. ### paulktreg Distinguished Member

Jun 2, 2008
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Homework?

(Show us a screenshot of your attempted solution).

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Sep 30, 2014
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4. ### Jony130 AAC Fanatic!

Feb 17, 2009
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Hi, to me your solution is wrong .
For Vd = 0.7V diode current is equal to
Id = (4*0.7V + 5*0.7^2) = 2.8 + 2.45 = 5.25mA
And resistor current
Ir = (5V - 0.7V)/200Ω = 21.5mA
So Id is not equal to Ir. and this means that your solution is wrong.
And the correct answer is Vd ≈ 1.51V because this time
Id ≈ 4*1.51V + 5*1.51V^2 ≈ 17.4405mA and Ir = (5V - 1.51V)/200Ω ≈ 17.45mA
And since Id≈Ir we have a correct solution.

Last edited: Oct 1, 2014
5. ### copper_pipe Thread Starter New Member

Sep 30, 2014
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where is the 1.51v coming from?

Feb 17, 2009
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7. ### MikeML AAC Fanatic!

Oct 2, 2009
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Or Let LTSpice solve that equation. The B1 behavioral current source has the same I/V behavior as the diode...

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10. ### copper_pipe Thread Starter New Member

Sep 30, 2014
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230 V * 1/5 = 46Vrms on the secondary

Output pk voltage will be 46 * sqrt(2)/pi = 20.70V = DC

RMS = 20.70V/2= 10.35V

P = I^2 * R = Vrms^2/R

P = 10.35^2/10 = 10.71W

Does this look correct to you guys?