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Two Zeners in Parallel?

B

Brad

Jan 1, 1970
0
Hi,

I need a 33V 1W zener diode to repair a Samsung TV GX1395
(in tuner 33V line). I have a bunch of 33V 1/2 W NTE5036A zeners.
Is there anything wrong with putting two 1/2W zeners in parallel?

I also have a 24V 1W and a 9V 1W. I thought about putting
those in series.

Thanks in advance, Brad

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M

Mark D. Zacharias

Jan 1, 1970
0
Brad said:
Hi,

I need a 33V 1W zener diode to repair a Samsung TV GX1395
(in tuner 33V line). I have a bunch of 33V 1/2 W NTE5036A zeners.
Is there anything wrong with putting two 1/2W zeners in parallel?

I also have a 24V 1W and a 9V 1W. I thought about putting
those in series.

Thanks in advance, Brad

Two zeners in parallel doesn't really work, since there is no way to
guarantee they will share current equally, or even share current at all.
More likely one diode will "zener" first, then effectively bypass the other.

Zeners in series, however, works fine in my experience.


Mark Z.
 
S

Sam Goldwasser

Jan 1, 1970
0
I need a 33V 1W zener diode to repair a Samsung TV GX1395
(in tuner 33V line). I have a bunch of 33V 1/2 W NTE5036A zeners.
Is there anything wrong with putting two 1/2W zeners in parallel?

The one with the slightly lower voltage will dissipate most of the power.
I also have a 24V 1W and a 9V 1W. I thought about putting
those in series.

That's better.

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A

Asimov

Jan 1, 1970
0
"Brad" bravely wrote to "All" (31 Mar 05 12:30:14)
--- on the heady topic of "Two Zeners in Parallel?"

Br> From: [email protected] (Brad)
Br> Xref: aeinews sci.electronics.repair:44575

Br> I need a 33V 1W zener diode to repair a Samsung TV GX1395
Br> (in tuner 33V line). I have a bunch of 33V 1/2 W NTE5036A zeners.
Br> Is there anything wrong with putting two 1/2W zeners in parallel?

Br> I also have a 24V 1W and a 9V 1W. I thought about putting
Br> those in series.


The series combination will work much better than the parallel. The
parallel zeners will tend to have one hog the current if their voltage
is the least bit different by only a few millivolts. Unless they are
perfectly voltage matched at the expected current it won't work right.

Another idea is to use a power transistor with a 32 or 33 volt zener
connected from the base to the collector. Most of the current will
flow through the transistor collector, with only the base current
flowing through the zener. As a side benefit the tempco is improved.

A*s*i*m*o*v

.... Dunno if we'll get that past the CSA und UL 'owever.
 
F

Franc Zabkar

Jan 1, 1970
0
Hi,

I need a 33V 1W zener diode to repair a Samsung TV GX1395
(in tuner 33V line). I have a bunch of 33V 1/2 W NTE5036A zeners.
Is there anything wrong with putting two 1/2W zeners in parallel?

I also have a 24V 1W and a 9V 1W. I thought about putting
those in series.

Many TV tuning circuits require temperature compensated reference
zener diodes, eg TAA550B, uPC574J. I'm not sure if a regular zener is
stable enough for these sets, even after allowing for AFT.


- Franc Zabkar
 
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