1N4148 Diode circuit

[JasonMcG]

Design and draw the appropriate circuit to be used in measuring the diode forward current I, using a 5V dc source to forward bias a 1N4148 diode, a 10k ohm potentiometer to vary the dc voltage and a 330 ohm resistor to limit the current through the diode.
Is this the correct circuit? If not, what is the correct circuit?
http://i1362.photobucket.com/albums/r687/JasonMcG1/1N4148_zpsdf8df1b0.png

 

[JasonMcG]

Design and draw the appropriate circuit to be used in measuring the diode forward current I, using a 5V dc source to forward bias a 1N4148 diode, a 10k ohm potentiometer to vary the dc voltage and a 330 ohm resistor to limit the current through the diode.
Is this the correct circuit? If not, what is the correct circuit?
http://i1362.photobucket.com/albums/r687/JasonMcG1/1N41482_zps73482f7e.png

 

[Harald Kapp]

Jason, I think this is homework, so I moved the thread.

To answer your question: I think it is not correct - and for homework I will not give you the correct circuit. I'm going to guide you to find it yourself.

You have the current limiting resistor in series with the diode: o.k.

You have a potentiometer in series with the diode: The potentiometer will limit the current through the diode, too. And by limiting the current it will reduce the voltage drop across the diode, too. So it might be used to change the DC voltage. Only I think the circuit is not intended to look like this. Since explicitely "vary the DC voltage" is requested in the text, the author probably is looking for a solution that uses the potentiometer together with the battery as a variable voltage source.
How could you use a potentiometer and a battery to create a variable voltage source? Once you've constructed this sub-circuit, connect the diode and the current limiting resistor to it.
Show us your result for verification.

Heads up

Harald

 

[JasonMcG]

The current limiting resistor and diode should be in series and the voltage source and potentiometer should be in series and the two parallel to each other?

 

[duke37]

No, R1 needs to be connected to the potentiometer slider.

Do you understand why?

 

[JasonMcG]

Please explain

 

[Laplace]

R1 could be connected to the battery. Isn't the best way to limit current through the diode by limiting current from the battery? Also, would it not be better to connect the diode to ground so that the measured voltage is ground-referenced?

 

[Harald Kapp]

The potentiometer is can be used as variable resistive divider to create a variable voltage from the fixed batttery voltage. The variable voltage is taken between the slider and one end of the potentiometer.

The current limiting resistor has to be in series with the LEd, It doesn't matter where in the circuit. You can place it between the battery and the potentiometer or between the potentiometer and the LED. Since in both cases the current through the LEd also has to flow through the resistor, the exact placement is irrelevant for the function (current limiting).

Note that there is not one single "correct" answer to the exercise. Several solutions can give the same result.

 

[JasonMcG]

Is this correct?
http://i1362.photobucket.com/albums/r687/JasonMcG1/1N41482_zps6289dd94.png

 

[Harald Kapp]

I'd say this look muuuuch better

 

[duke37]

That looks better. Do you understand why?

 

[JasonMcG]

All explanations welcome

 

[Laplace]

"All explanations welcome" is what we say to you; however, we would prefer that you provide the correct explanation.