# i cant understand this Solution plz help me kindly..

#### posof

Joined Mar 31, 2011
7
hello! actually im not good at english but i really needed to come here to ask this problem. plz understand my poor english

i attatched two pictures. One of them is a circuit my problem and the other one is a solution of the problem. Assume constant-voltage model

the problem is ploting the currents flowing through R1 and D1 as a function of Vin for the circuit.

but i cant understand how does current flow throgh R1 when D1 turn on. i thought this worng cuz D1 would operate like a short line...
Am i right? or the solution is correct?

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#### atferrari

Joined Jan 6, 2004
4,666
You could assemble the circuit and test yourself instead of asking. It is simple really!

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#### StayatHomeElectronics

Joined Sep 25, 2008
1,073
Can you explain what the constant voltage model is? If you assume that there is a voltage across the diode when it is on, for example 0.7volts, then it is easy to see how there is current flowing in R1.

#### posof

Joined Mar 31, 2011
7
oh.. i see.. i wasnt aware of the meaning of constant diode model. thank you so much! i really happy to join this community.

#### posof

Joined Mar 31, 2011
7
I used multisim Tool and found there is a current. really there is thank you for your kindness.

#### bglazierjr

Joined Apr 2, 2011
6
Of course theres a current. Lets say you have a silicon diode. The assumed drop across a silicon diode is 0.7V as previously mentioned. R1 and the diode are connected at both nodes so that means they have the same voltage drop. If you know resistance value of R1 than you can take the 0.7V / R1 and find the current.

Also if your reverse biasing the diode than you can think of it more as an open circuit, meaning all the current will flow the R1 instead. I hope you find this helpful.