Re: Zener Heat
From: Tim M (tym1_at_spammenot.cwru.edu)
Date: 02/12/05
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Date: Sat, 12 Feb 2005 17:19:33 -0500
36 mA?
-Tim
amdx wrote:
>>I'm feeding it with approx. 155 VDC, and the string of >zeners adds up to
>
> 146.4 (at test conditions there's 149 >V across them, which is close enough
> for me).
>
> Oh!, 12-6volt and 6-12 volt = 144volt
>
> > I only have 1/4-W resistors handy, so the test setup
>
>>has two 330-ohm resistors in parallel to give 165-ohm at 0.5 W.
>
>
> So you have about 6v across 165 ohms or about 3.6 milliamps through the
> string at no load.
>
> If you connected a 40ma load at the 72 volt junction
> the voltage at the top of the string would start to drop below the 155volt
> supply voltage and the string would stop functioning properly. I'm sure your
> running this close to keep heat low in the string.This would happen even if
> you spread out the load among several zener junctions.
> The 12volt zener at the top of the string would have about a half watt
> across it, which is ok.
> Well Tim, now that I've went through this I think you need to find a way
> to cool your zeners (sorry, I guess you new that ;-).
> If it's a one of unit, you might bend a thin u shaped piece of alum.
> around each diode. Such as,
> poor ascii art. l_o_l The vertical sections will help get rid of
> the heat.
>
> I'm curious why you need such high voltages for ICs.
>
> I don't have any ideas other than heat sinking.
> Mike
>
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