A Simple Diode Problem

[AbhinavRajan]

I have a very simple diode problem in my assignment.
It seems to be very easy but I am unable to find the answer.
I seem to miss something very simple/obvious.
Could someone tell me how to arrive at the answer for the question?
Please help!
Thanks in advance!

https://www.coursera.org/learn/electronics/quiz/XNuwv/problem-4-3-1

 

[c_mitra]

You should try to solve problems given as course work all by yourself. Getting the problem solved by others is considered unfair means.

When Vs is low, the diode is reverse biased and does not conduct. To conduct, the diode must become forward biased. It becomes forward biased only when Vs becomes greater than 10 (the battery voltage).

Vs is a given a function of time: 2t-1; 2t-1=10 or t=5.5. This is the time the diode starts to conduct. If you are looking for integral number as the result, put t=6.

As this is an ideal diode, we have not considered the diode drop (it needs a little extra voltage to conduct).

 

[CataM]

Another way to see this is to subtract the voltage sources i.e. V TOTAL = 2t-1 - 10.
When does the diode conduct? As it is ideal, as mitra said, when V TOTAL > 0 i.e. 2t-1 - 10 > 0 <=> t > 5.5