diyAudio

diyAudio (https://www.diyaudio.com/forums/index.php)
-   Solid State (https://www.diyaudio.com/forums/solid-state/)
-   -   Mounting a small signal diode on heatsink - need suggestion (https://www.diyaudio.com/forums/solid-state/154360-mounting-signal-diode-heatsink-suggestion.html)

IG81 2nd November 2009 11:58 PM

Mounting a small signal diode on heatsink - need suggestion
 
Hello,

I am currently designing a class-A power amplifier.

I was looking to mount the diodes, that I plan to use in the current source that will set the output stage bias, on the heatsink, in order to thermally compensate the BJT's.

I am looking for suggestions as to how to physically mount the diodes on the heatsink.

Thanks!

ig

Conrad Hoffman 3rd November 2009 12:03 AM

The old solution was to use diodes in a metal can and a small metal strap clamp. The old SWTPC Tiger amps did this. You could pot the diodes in a small piece of brass tubing and do the same thing using thermally conductive epoxy. You could wrap the diode in a piece of Sil-Pad type material and use a flat spring clamp. You could also find a suitable diode in a TO-220 case and mount it in the conventional way. You could use one junction of a small metal body transistor.

GK 3rd November 2009 12:43 AM

Or just connect a TO-126 transistor such as a cheap BD139 as a diode (c-B) and use that.

syn08 3rd November 2009 12:59 AM

Quote:

Originally Posted by GK (https://www.diyaudio.com/forums/solid-state/154360-mounting-signal-diode-heatsink-suggestion-post1968278.html#post1968278)
Or just connect a TO-126 transistor such as a cheap BD139 as a diode (c-B) and use that.

B-E would be better. Vbe tempco has little variation from device (e.g. BD139) to device (e.g. 2SC5200).

GK 3rd November 2009 01:12 AM

When using a transistor as a diode you generally connect the collector to the base.

Enzo 3rd November 2009 04:07 AM

Well now, GK, I am unclear on your suggestion now.

Are you saying to connect using the collector AND base as a diode? (as implied in post #3) Or are you suggesting they connect the base TO the collector, leaving the B-E junction as the diode? (as implied in post #5, which was the suggestion syn08 made)

In other words, do you want to say connect the collector to the base, or do you want to say connect to collector and base?

jerluwoo 3rd November 2009 06:29 AM

Yes GK is saying to connect the base to the collector and use the BE junction as the diode.

GK 3rd November 2009 06:43 AM

Yes, sorry, by “(C-B)” I meant collector connected to base. I just figured everyone would know that already :D

IG81 3rd November 2009 12:17 PM

Thanks alot guys, it didn't even occur to me to use a transistor junction, duh!

That will greatly facilitate heatsink mounting.

ig

IG81 3rd November 2009 12:53 PM

In addition to the above, I assume the best transistor to use as a diode would be the same model as the output transistor to bias, as they will exhibit the same temperature coefficient. Would that just be splitting hair, or would any cheaper transistor behave close enough to be almost just as good?

And when it comes to setting the current through the "diode transistors", I guess the Ic v.s. Vbe plot in the spec sheet is what I should look at to make the initial prediction to determine Vbe voltage drop right? And I would assume the former is the reason why the collector should be tied to the base in this situation.

Thanks,

ig


All times are GMT. The time now is 01:20 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 17.65%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio

Wiki