Diode Circuit Analysis..

[randolfo]

I am new in electronics, i am not sure if i am interpreting this circuit correctly. See circuit attached. When will the lamp will light up ?

1) S2 is closed and S1 is in position B
2) S2 is closed and S1 is in position A or position B.
3) S2 is closed and S1 is in position A.
4) S2 is closed and S1 is in position A, position B, or position C.

I am inclined to choose no. 2 , because I think if it is on position C current will be grounded and the diode will not conduct , so the lamp will not light on. Is my reasoning correct? Please give me some thoughts about this so I could learn better.. Thank you.

 

[ericgibbs]

I am new in electronics, i am not sure if i am interpreting this circuit correctly. See circuit attached. When will the lamp will light up ?

1) S2 is closed and S1 is in position B
2) S2 is closed and S1 is in position A or position B.
3) S2 is closed and S1 is in position A.
4) S2 is closed and S1 is in position A, position B, or position C.

I am inclined to choose no. 2 , because I think if it is on position C current will be grounded and the diode will not conduct , so the lamp will not light on. Is my reasoning correct? Please give me some thoughts about this so I could learn better.. Thank you.

hi,
You have made the right reasoning , but chosen the wrong answer.

Relook at #3

BTW: the diode is actually an SCR.

 

[randolfo]

Thanks. I thought it was just an ordinary diode, he he. What about answer no. 1, is there any explanation why it would not light up the lamp?

 

[ParkingLotLust]

The gate-to-cathode voltage needs to be higher than a certain amount (lets say 5v). When the switch is in position B, as in answer 1, the gate gets 0v, so it wont turn on. However, when the switch is in position A, as in answer 3, the gate would get the amount it needs, and will switch on until the holding current drops below a specified value.