# Diode question

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#### hupsenfg

##### New Member Hi i think if I would like to find Vd and Id, i can replace the diode with a 0.7V voltage source. How then should I proceed to do this question?
Thank you

#### hupsenfg

##### New Member
For Id, it should (5v-0.7v)/ 10k right?? Or we can ignore 0.7v

And Vd = 5v? After voltage divider

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#### ericgibbs

##### Well-Known Member
hi hup,
It asks for Vd, but it states 'assuming a practical diode', which suggests a diode with a 0.7v forward voltage drop.

The circuit diagram shows Vd across the diode, so Vd must be 0.7V

E

#### ci139

##### Active Member
FIG.1
is't like 10kΩ || (10kµ+diodeΩ) -- where the first 10k & 5k likely can be considered as "primary voltage divider" and
the second 10k and the (BW or FW)diode as the secondary voltage divider for voltage drop on the first 10k ... PS! the foreward diode is usually some 2k55 ohms (i donno for this circuit . . . the LT Spice shows so at 5V total supply for 1N4148)

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#### Ratchit

##### Well-Known Member
View attachment 108465
Hi i think if I would like to find Vd and Id, i can replace the diode with a 0.7V voltage source. How then should I proceed to do this question?
Thank you

It should be OK to give you the correct answer since a month has passed since you asked for help.

The diode will definitly turn on, because if it were off, there would be 20/3 volts across it. Use node analysis to find the voltage Vo. The equation is: The solution is Vo = 4.825 volts

Next find the current present in the diode. The solution is Id = 0.0005015 amp or about half a milliamp.

Note: If you gave me the saturation current of the diode, I would not have to make an estimate of 0.7 volts across the diode. I could calculate the diode voltage by the current present within it.

Ratch

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