Question

D 4.37. Assuming the availability of diodes for which vD = 0.75 V at iD = 1mA, design a circuit that utilizes four diodes connected in series, in series with a resistor R connected to a 15-V power supply. The voltage across the string of diodes is to be 3.3 V.

Answer 1

R = 0.5825 k ohm

Step-by-step explanation:

given data

vD = 0.75 V

iD = 1mA

resistor R = 15-V

solution

we get here first vD that is

vD =
`(3.3)/(4)`

vD = 0.825

so

iD = Ise ×
`e^{(vD)/(nvT)}`

n = 1

so we can say

`(iD2)/(iD1) = e^{(vD2-vD1)/(nvT)}`

so it will

iD2 = iD1 ×
`e^{(vD2-vD1)/(nvT)}`

put here value and we get

iD2 = 1 ×
`e^{(0.825-0.75)/(25)}`

iD2 = 1 ×
`e^(3)`

iD2 = 20.086 mA

so

R will be

R =
`(15-3.3)/(ID)`

R = 0.5825 k ohm