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# Newbie quesion - a query with a circuit

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#### varun.s.murthy

##### Newbie level 3
Newbie quesion

Hello everyone,
I am new to electronics and had a query with a circuit. Am attaching the query as an image here.

According to me,
When Vi > 0 , V = 1
When Vi < 0 , V = Vi

So is the answer (A) ?

Would be glad for any help.

<<Am really new here, so if there is anything wrong with the post/ the query is too simple,please let me know>>

Newbie quesion

i don't know , the answers are not clear ,

what does max(Vi,1) means?

Newbie quesion

max(Vi,1) is a function whose value will be the maximum of either Vi or 1

In other words
max(Vi,1) = Vi if Vi > 1
1 if Vi<1

Similarly for the min function.

Re: Newbie quesion

Look!:

If diode is conducting then V=Vin (because diode is ideal), the current through the first resistor is

Vi/1 and the current through the diode is 1-Vi . This current is positive; that is

1-Vi > 0

Vi < 1

Now, if diode is off, then the reverse voltage through de diode is -V+Vi and this is positive; that is:

-V+Vi>0 , but V=1A*1Ohm (due to current source), then:

Vi > 1

### varun.s.murthy

Points: 2
Newbie quesion

The circuit is too simple.
The diode is reverse-biased so it does nothing.
Since there is 1A in 2 ohms then use Ohm's Law to calculate the input voltage.
Hint: 1A x 2 ohms= 2V.

If the question is multiple choice then you should have said so.

Re: Newbie quesion

Thanks everyone for helping me out with this.

Audioguru:

Excuseme, but you are wrong, diode is on or off because Vin may be positive (Vi >1 in this case) or less than 1V, then the answer is A).

jardila said:
Audioguru:

Excuseme, but you are wrong, diode is on or off because Vin may be positive (Vi >1 in this case) or less than 1V, then the answer is A).
No.
The input voltage is shown as positive. Therefore the diode is reverse-biased and does nothing.
The current in the 2 ohms is 1A so the input voltage is 2V.

Audioguru said:
jardila said:
Audioguru:

Excuseme, but you are wrong, diode is on or off because Vin may be positive (Vi >1 in this case) or less than 1V, then the answer is A).
No.
The input voltage is shown as positive. Therefore the diode is reverse-biased and does nothing.
The current in the 2 ohms is 1A so the input voltage is 2V.

NO. That is only the polarity , but Vi is a variable an may be any value (the polarity shown in the circuit and that does not mean is positive voltage).

Thanks.

Don't worry Audioguru, I agree with your answer, based on the information given.

It must be the 'new math' they teach these days, it's no wonder so many people have problems.

Brian.

I'd have to agree with Audioguru.

If there were negative voltage the current would be traveling in the opposite direction (away from the reference). The fact that the current is traveling to the reference would lead me to believe that the voltage is positive, therefor making the diode reverse-biased.

betwixt said:
Don't worry Audioguru, I agree with your answer, based on the information given.

It must be the 'new math' they teach these days, it's no wonder so many people have problems.

Brian.

Unfortunatly have many problems in simple exercises like this. I do not pretend to explain basis of electronics, I explained solution and it is correct.

Re: Newbie quesion

Audioguru said:
The circuit is too simple.
The diode is reverse-biased so it does nothing.
Since there is 1A in 2 ohms then use Ohm's Law to calculate the input voltage.
Hint: 1A x 2 ohms= 2V.

If the question is multiple choice then you should have said so.

If the exercise says that the voltage source is the input voltage, it means that we must not to find this voltage; the exercise asks about the voltage across the resistence, not the INPUT VOLTAGE, for that reason. The asumption that the input voltge is 2V means that there isn't any voltage across the current source. For that reason I agree with the jardila's answer.

Re: Newbie quesion

Audioguru said:
The circuit is too simple.
The diode is reverse-biased so it does nothing.
Since there is 1A in 2 ohms then use Ohm's Law to calculate the input voltage.
Hint: 1A x 2 ohms= 2V.

If the question is multiple choice then you should have said so.

I think that some people have problems with fundamentals circuits, obviously your answer is wrong.

I agree with jardila, the correct answer V=min(Vin,1)

There is no current source.
There is a voltage source with the polarity shown to reverse-bias the diode, a reverse-biased diode that does nothing, two 1 ohm resistors with the polarity across one shown and a current meter that shows 1A.

The phrases are not good English and do not mean anything. What is "Vi, 1"?

I see a big curent source of 1Amp in the diagram. I don't kwon what circuit are you seeing.

The circle with an arrow inside and a "1A" label is an Amp-meter, isn't it?

Audioguru said:
The circle with an arrow inside and a "1A" label is an Amp-meter, isn't it?

No. That is a current source of 1A. the amp-meter's symbol is a circle with a letter "A" inside instead an arrow.

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