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?
https://i1362.photobucket.com/albums/r687/JasonMcG1/1N4148_zpsdf8df1b0.png

 

[crutschow]

Your circuit has the pot across the 5V source in parallel with the other resistor and diode so the pot has no effect on the diode current. And the diode and resistor are also connected directly to the 5V source so the voltage to and current through the diode are fixed. Since the pot wiper is the variable part of the pot, don't you think that should be connected to vary the voltage to the resistor and diode?

Think about how the current flows and give it another try.

 

[JasonMcG]

Like this?
https://i1362.photobucket.com/albums/r687/JasonMcG1/1N41482_zps73482f7e.png

 

[Nigel Goodwin]

Like this?
https://i1362.photobucket.com/albums/r687/JasonMcG1/1N41482_zps73482f7e.png

No, try again - and post your picture on the forum, not a third party site - click on 'upload a file'.

 

[JasonMcG]

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

 

[cowboybob]

You're getting warmer.

...Since the pot wiper is the variable part of the pot, don't you think that should be connected to vary the voltage to the resistor and diode?

 

[JasonMcG]

Like this?

 

[cowboybob]

No. But you're getting closer.

Think of your circuit as two circuits: one supplying a variable voltage level, the other using it, both with a common ground.

HINT: It's about the only circuit variation left...

 

[JimB]

Have a look at the attachment.

JimB

 

[JasonMcG]

?

 

[cowboybob]

Bingo!

Congratulations...

 

[JasonMcG]

Have a look at the attachment.

JimB
View attachment 84669

.

 

[JasonMcG]

If you had to design a circuit to forward bias an LED which is made up of a dc supply, potentiometer, 330 ohm resistor and an LED in series. The potentiometer being used to vary the bias voltage across the LED. It would be then same circuit?

 

[JimB]

If you had to design a circuit to forward bias an LED which is made up of a dc supply, potentiometer, 330 ohm resistor and an LED in series. The potentiometer being used to vary the bias voltage across the LED. It would be then same circuit?

I am not sure if that question is aimed at me, but yes, I would use your final circuit.
I think that I would use a lower resistance potentiometer.
Without doing some calculations, intuition tells me that as the diode conducts, all adjustment will be cramped up at one end of the 10k pot.

JimB

Edit, sorry I misinterpreted the question which has switched from a 1N4148 to an LED.
Yes, use the same circuit for the LED.

 

[KeepItSimpleStupid]

Power switch, anybody?

 

[JasonMcG]

Thanks for the help! Appreciate it

 

[MrAl]

Hi,

Just to note, usually a pot is wired as a variable resistor in series with the diode or LED. No need to wire the pot across the voltage source which wastes energy.

 

[KeepItSimpleStupid]

MrAl

Nice catch. Wire it as a crude current source.