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Do 2 x 1 watt diodes = 1x 2 watt ZD?

S

shannell

Jan 1, 1970
0
I am trying to get a 2 watt 5.1 volt zener diode, I bought 2 x 1 watt zener
diodes, if I put them in parrallel, do they work the same as a 2w 5.1v ZD?
 
K

Ken Taylor

Jan 1, 1970
0
shannell said:
I am trying to get a 2 watt 5.1 volt zener diode, I bought 2 x 1 watt zener
diodes, if I put them in parrallel, do they work the same as a 2w 5.1v ZD?
In theory, yes, but it's not a good practice as they aren't perfect devices
and won't load share 100%. What are you actually trying to do? There may be
a better solution.

Ken
 
S

shannell

Jan 1, 1970
0
Hi, I am trying to quieten the 80mm 12v fans on a CRT projector.
Any reccommendations? Dick smith only had the 1 watters...
 
J

Justin Thyme

Jan 1, 1970
0
shannell said:
I am trying to get a 2 watt 5.1 volt zener diode, I bought 2 x 1 watt zener
diodes, if I put them in parrallel, do they work the same as a 2w 5.1v ZD?
Unfortunately no - they have a tolerance in them, so one might be 5.11v and
the other 5.09v. When they are in parallel, the 5.09v one will take all the
current, because the voltage is still below the threshold of the 5.11v.
Consequently one zener will be drastically overloaded while the other does
nothing at all.
There are ways around it however - careful use of appropriate value
resistors can overcome the problem. i'm not the best at doing ascii circuit
diagrams, and it's maybe a little hard to explain. if you want more info
i'll post a sketch on the web and give you a link.
Alternatively - have you considered the use of 7805 devices? - they are
simple to design around and can comfortably deliver fairly high currents -
up to 1A with suitable heatsinking.
 
R

Rod Speed

Jan 1, 1970
0
Justin Thyme said:
Unfortunately no - they have a tolerance in them, so one might be 5.11v and
the other 5.09v. When they are in parallel, the 5.09v one will take all the
current, because the voltage is still below the threshold of the 5.11v.
Consequently one zener will be drastically overloaded while the other does
nothing at all.

Not in his situation where he's just chucking some voltage away.

It should work well enough.
 
J

Joseph Webster

Jan 1, 1970
0
Would be better to put two with half voltage in series.
Much more tolerant to small differences between diodes.

JLW
 
R

Rod Speed

Jan 1, 1970
0
James Fenech said:
Hello,

A better bet may be two lower voltage zenner in series.

True. Dunno how available they are tho.
 
A

amstereo - matt2

Jan 1, 1970
0
crt projectors get HOT!!! do you really want to put more heat stress on the
unit, best thing to do is get a quieter fan or mod the air-flow path a bit.
 
F

Franc Zabkar

Jan 1, 1970
0
Not in his situation where he's just chucking some voltage away.

"Chucking some voltage away"? What a load of gibberish.
It should work well enough.

No, it is a silly idea.


- Franc Zabkar
 
S

Spajky

Jan 1, 1970
0
Hi, I am trying to quieten the 80mm 12v fans on a CRT projector.
Any reccommendations? Dick smith only had the 1 watters...

see my site under electronics; fan stuff II next page, dirty zener
enhancement ...

-- Regards, SPAJKY
& visit site - http://www.spajky.vze.com
Celly-III OC-ed,"Tualatin on BX-Slot1-MoBo!"
E-mail AntiSpam: remove ##
 
J

John Crighton

Jan 1, 1970
0
Hi, I am trying to quieten the 80mm 12v fans on a CRT projector.
Any reccommendations? Dick smith only had the 1 watters...

Hello Shannell,
Ken's question was spot on.
Have a look here for starters.
http://casemods.pointofnoreturn.org/pwm/index.html
Have a look at the LM317 tutorial if you don't like the PWM circuits.

If you don't like the LM317 idea, maybe a string of several ordinary
diodes in series would do. You could mount them on a rotary
switch. Introduce roughly 0.8 volt (drop across each diode) on
each click of the switch till the fan noise reduces to suit you.

I see DSE has 1 amp diodes for 7 cents each and 3 amp diodes
for 25 cents. How much current does your fan draw?
Find out and choose your diodes.

Here is another site where the author has gone
into this fan noise problem in a big way also.
http://www.cpemma.co.uk/index.html

Have fun!

Regards,
John Crighton
Hornsby
 
shannell said:
Hi, I am trying to quieten the 80mm 12v fans on a CRT projector.
Any reccommendations? Dick smith only had the 1 watters...

Reduction of the airflow into the projector could shorten the lifetime
of some components due to elevated heating of these components. These
could be lamps, the crts, which would probably depend on circulation
of cooling fluids on the screen of the tube via convection anyway,
electrolytic capacitors, most semiconductors, etc.

If you can try to find out the manufacturer of the fans, and the model
of the fan, then you can identify the amount of airflow the fan pushes
into the projector. You could then attempt to select a low noise fan
that has an airflow (typically measured in litres/minute|hour) that
is equivalent or greater than the existing fans. Low noise fans typically
have lower flow rates than equivalent size fans.

RS Components and Farnell have a selection of 80mm fans, both 240 volt ac,
and 12 volt dc. Others in this ng could recommend other suppliers.

Then again, if you modify the projector in any way, you could void the
warranty, if it's still valid. If it's out of the warranty period, then
I'd recommend you employ a qualified tv technician/repairman to carry
out the required modifications. Also, there may be a modification
sheet from the projector manufacturer that details how to fix a noisy
fan problem.

--

Regards
David

=================================
Reply to

dmmilne at ozemail dot com dot au
 
A

Arpit

Jan 1, 1970
0
use a slower speed 120mm fan. quieter, and more airflow.
 
R

Rod Speed

Jan 1, 1970
0
Some stupid wog claiming to be
message just the puerile shit thats always pouring from its lard arse.
 
F

Franc Zabkar

Jan 1, 1970
0
Hi, I am trying to quieten the 80mm 12v fans on a CRT projector.
Any reccommendations? Dick smith only had the 1 watters...

FWIW, WES Components have 5W, 5.1V Zeners for ~$1 each. You could also
make up a string of eight 1N4004 diodes in series. Having said that, I
believe reducing the airflow is not a good idea.


- Franc Zabkar
 
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