How to explain that the measurement Vf ( P to N ) is 3.3V now

Hi All,

There is a PN diode, P connects 3.3V, N connects to ground. We knew that Vf is 0.7V.

How to explain that the measurement Vf ( P to N ) is 3.3V now but not

0.7V ...

Best regards, Boki.

Reply to
Boki
Loading thread data ...

do you have a resistor in series with the diode, If not you release the magic smoke from the PN junction

martin

Reply to
martin griffith

formatting link

martin

Reply to
martin griffith

By definition, if you hook the anode to a stiff enough voltage source, that's what happens. Depending on the details of the diode, you probably have a number of amps going through it and it's getting pretty warm.

Put more amps through and it will become a "Noise Emitting Diode" (NED) in the lexicon. As in "hook to a stiff enough voltage source and it emits a loud noise, once." And not conduct at all anymore.

Everybody else here has blown up diodes, popped the top off of expensive chips with lots of magic smoke coming out, filtered AC with electrolytics (making confetti and a gooey residue) etc.

Tim.

Reply to
Tim Shoppa

Just for the heck of it I just connected a 1N4148 directly to a 3V3 bench supply. The current was limited to about 2.6A and the diode started glowing and became a short, not open. It was funny to see how the reddish inside of the diode became black and then turned red again when the power was switched off. Part of it was gone. The text on the diode disappeared completely.

--DF

Reply to
Deefoo

How about use transistor, and put a resistor on collector ( NPN )

The Vbe now is 3.3V.

emitter to ground directly.

Boki.

Reply to
Boki

Boki -

If you are reverse engineering a device (and I'm guessing you are), then with 99% certainty if the device is still functioning then you've got one of those SMT transistors with built-in base resistor. Typically for a NPN switch the base resistor is in the few k to few hundred k ohm range, depending on what sort of voltages get are being put in and what sort of current is being switched.

With 3.3V going in and say a 50mA current being switched, you'd probably end up with a base resistor in the low 1000's of ohms for a base current in the 1mA region.

I know you like to write cryptic questions, but from your questions there's no secret that you are spending a good chunk of your time reverse engineering stuff, so couching all this in your gobbledygook really isn't helping you.

Tim.

Reply to
Tim Shoppa

How about buying an electronics engineering text book?

--DF

Reply to
Deefoo

I think it is a good chance to know more here, but not limited to reverse engineering : )

Reply to
Boki

Haha..

Reply to
Boki

Boki, Are you really that ignorant?

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
 Click to see the full signature
Reply to
Jim Thompson

Please take easy, I can still get some : )

Reply to
Boki

Gallium nitride.

Tim

--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
 Click to see the full signature
Reply to
Tim Williams

Be grateful for the air compressor and puncture repair kit.

Ken

Reply to
Ken Taylor

Let me see, i have blown up several transistors (including a to-3), many resistors and capacitors in various ways. Never connected an electrolytic to AC, connected a few to way above rated voltage (15V part to over 60V), (toxic, had i known at the time) confetti all over the garage. Expensive IC's however were lost to ESD (previous adventures had taught me to more careful / respectful of expensive parts; i was just a tween).

--
JosephKK
Gegen dummheit kampfen die Gotter Selbst, vergebens.  
 Click to see the full signature
Reply to
joseph2k

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.