looking for a diode that has 3 diodes for a 1.5 volt drop

[versuviusx]

hey i'm looking for a small signal diode that has 3 diodes in it so i can get a 1.5 volt drop. if you know which diode i can use to get this affect that would be awesome!

 

[JohnRoberts]

Dual diodes are pretty common, and I have used inexpensive red LEDs before to make 2.1V drops. I think there are some LEDs around 1.8V but that's more than your desired 1.5V, perhaps such a LED but at very low current?

Good luck..

JR

 

[dshay]

i'm just a tech in training, but wouldn't two silicons in series give you 1.4V?

 

[burdij]

A red LED will drop approximately 1.5V.

 

[JohnRoberts]

[quote author="dshay"]i'm just a tech in training, but wouldn't two silicons in series give you 1.4V?[/quote]

A diode drop is commonly considered as .5V or .6V DC nominal, but in fact varies with current. I don't have the full equation committed to memory but a very large increase in current results in a small, but real, increase in voltage.

This voltage to current relationship is used in log conversion, etc. As it has a linear with dB relationship (mostly).


JR

 

[JohnRoberts]

[quote author="burdij"]A red LED will drop approximately 1.5V.[/quote]

Last time I looked at this red was still more than 1.5V (nominal), but green and yellow, were lower voltage than red, so perhaps close to 1.5V at modest current.

JR

 

[bcarso]

Depends on the specific material. The nominally lower brightness (i.e., lower "luminous efficacy") diodes made of GaAsP ("standard red") are about 1.6V for a midrange current, and have the advantage of a close match to a Si base-emitter temperature coefficient. Hence if they are used as bias sources you get a pretty decent zero tempco overall, depending on the circuit.

But there are superbright reds that have higher nominal forward voltages and not-quite-so-good-match tempcos.

 

[beatpoet]

Don't some germaniums give you @ .4V drop per diode?

 

[Samuel Groner]

As already mentioned a red LED is the part you're looking for. You might want to check this thread as well: www.groupdiy.com/index.php?topic=9121

Or use a TLV431.

Samuel

 

[clintrubber]

Maybe the application has enough room for a Vbe-multiplier ? Make any drop you want...

 

[JohnRoberts]

I would only offer that all red LEDs are not the same, so you may need to sample a few. As Brad mentions perhaps avoid the high efficiency reds. In my experience colored LEDs ran lower than reds, but do what works for you.

I recently was messing with a multi color LED bar for a meter application I was working on, and these were all higher than 1.5V. I happen to have a detailed data sheet and the first thing I notice is the red LEDs are actually orange, and all three LED colors spec around 1.9-1.95V @ 10 mA. FWIW I measured less forward voltage drop on the bench, though I was running slightly cooler than rated 10 mA.

JR

 

[gyraf]

The 1.5V zener in the SSL 4000 channel compressor has a strange property - the stripe-marking on the diode itself seems to have been put on randomly, and this goes for replacement 1V5 zeners I've seen as well.. :?

The old schemo even says :"marked polarity may differ" or something like that..

http://gyrafaudio.googlepages.com/SSL-E-Dynamics-82E10.gif/SSL-E-Dynamics-82E10-full.gif - look by the RMS-converter

Jakob E.

 

[emorysmith]

Maybe 2 or 3 Mot MZ2367. If they still make 'em.
I remember they have a higher drop than 2x 1N400x but less than 3.
Used to use them in bias circuits for power amps.
:guinness: