| Author |
Message |
Tim M
Guest
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 Posted:
Sat Feb 12, 2005 12:57 pm Post subject:
Zener Heat |
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I'm designing a power supply that involves putting a bunch of zeners in
series, specifically 6 1N4742As (12V, 1W) and 12 1N4735As (6.2V, 1W).
Yes, I know that's a lot of zeners, but current drain of my circuit is
only 40-50 mA. However, I notice the zeners getting very hot, even
though I'm well below the max power dissipation per diode.
What sort of heat sinking considerations should I be taking. The
1N4742As are glass, the others metal. I have them laid out next to each
other lengthwise (see below), which probably wasn't the best choice for
heat dissipation.
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Thanks,
Tim
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Pooh Bear
Guest
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| Posted:
Sat Feb 12, 2005 1:31 pm Post subject:
Re: Zener Heat |
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Tim M wrote:
| Quote: | I'm designing a power supply that involves putting a bunch of zeners in
series, specifically 6 1N4742As (12V, 1W) and 12 1N4735As (6.2V, 1W).
Yes, I know that's a lot of zeners, but current drain of my circuit is
only 40-50 mA. However, I notice the zeners getting very hot, even
though I'm well below the max power dissipation per diode.
What sort of heat sinking considerations should I be taking. The
1N4742As are glass, the others metal. I have them laid out next to each
other lengthwise (see below), which probably wasn't the best choice for
heat dissipation.
|
Indeed.
Heat dissipating components need to be separated by a respectable distance
on a pcb.
You may improve heat dissipation by using more copper foil around each
component leg.
I had a guy lay out a pcb for me with a 1W3 zener run at about 70%
dissipation. Despite my requests, he didn't allow much space for the pads.
Luckily it was simply a prottoype. The leads of the zener virtually *welded*
themsleves to the pcb ! I'm not kidding either !
Component ratings are entirely dependent on mounting /orientation /airflow -
etc etc.......
Graham |
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Tim M
Guest
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| Posted:
Sat Feb 12, 2005 2:25 pm Post subject:
Re: Zener Heat |
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I was also thinking of making a (long) heat sink out of aluminum and
having it contact the package of each zener, probably with some heat
conductive paste in between. With the devices so closely spaced, there
isn't a lot of working room at the leads.
-Tim
Pooh Bear wrote:
| Quote: | Tim M wrote:
I'm designing a power supply that involves putting a bunch of zeners in
series, specifically 6 1N4742As (12V, 1W) and 12 1N4735As (6.2V, 1W).
Yes, I know that's a lot of zeners, but current drain of my circuit is
only 40-50 mA. However, I notice the zeners getting very hot, even
though I'm well below the max power dissipation per diode.
What sort of heat sinking considerations should I be taking. The
1N4742As are glass, the others metal. I have them laid out next to each
other lengthwise (see below), which probably wasn't the best choice for
heat dissipation.
Indeed.
Heat dissipating components need to be separated by a respectable distance
on a pcb.
You may improve heat dissipation by using more copper foil around each
component leg.
I had a guy lay out a pcb for me with a 1W3 zener run at about 70%
dissipation. Despite my requests, he didn't allow much space for the pads.
Luckily it was simply a prottoype. The leads of the zener virtually *welded*
themsleves to the pcb ! I'm not kidding either !
Component ratings are entirely dependent on mounting /orientation /airflow -
etc etc.......
Graham
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me
Guest
|
| Posted:
Sat Feb 12, 2005 5:37 pm Post subject:
Re: Zener Heat |
|
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| Quote: | I'm designing a power supply that involves putting a bunch of zeners
in series, specifically 6 1N4742As (12V, 1W) and 12 1N4735As (6.2V,
1W). Yes, I know that's a lot of zeners, but current drain of my
circuit is only 40-50 mA. However, I notice the zeners getting very
hot, even though I'm well below the max power dissipation per diode.
|
Did anyone mention that that is a really stupid design, and why is he
running 40-50 ma through them all??????
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Mook Johnson
Guest
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| Posted:
Sat Feb 12, 2005 6:58 pm Post subject:
Re: Zener Heat |
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Some quick math shows that your zeners will drop about 145 volts
collectively and pass 50mA which is 7.3 watts.
Even a power transistor mounted to a standard PCB will show significant
temperature rise.
Do you realize that you 12 volt zeners are disipating twice the power as
your 6.2 volt zeners (do you run out of 12s and started throwing in 6s to
fill in?).
Remember that power rating is making assumptions as to the temperature and
haet dissipating ability of what it is soldered too. look at the derating
curve for your 12V diodes and measure the lead temperture at the PCB and
I'll bet you're outside the recommended operating range.
"Tim M" <tym1@spammenot.cwru.edu> wrote in message
news:cuk9dh$fmq$1@eeyore.INS.cwru.edu...
| Quote: | I'm designing a power supply that involves putting a bunch of zeners in
series, specifically 6 1N4742As (12V, 1W) and 12 1N4735As (6.2V, 1W). Yes,
I know that's a lot of zeners, but current drain of my circuit is only
40-50 mA. However, I notice the zeners getting very hot, even though I'm
well below the max power dissipation per diode.
What sort of heat sinking considerations should I be taking. The 1N4742As
are glass, the others metal. I have them laid out next to each other
lengthwise (see below), which probably wasn't the best choice for heat
dissipation.
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--- --- ---
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Thanks,
Tim |
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R.Lewis
Guest
|
| Posted:
Sat Feb 12, 2005 7:34 pm Post subject:
Re: Zener Heat |
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"Tim M" <tym1@spammenot.cwru.edu> wrote in message
news:cuk9dh$fmq$1@eeyore.INS.cwru.edu...
| Quote: | I'm designing a power supply that involves putting a bunch of zeners in
series, specifically 6 1N4742As (12V, 1W) and 12 1N4735As (6.2V, 1W).
Yes, I know that's a lot of zeners, but current drain of my circuit is
only 40-50 mA. However, I notice the zeners getting very hot, even
though I'm well below the max power dissipation per diode.
What sort of heat sinking considerations should I be taking. The
1N4742As are glass, the others metal. I have them laid out next to each
other lengthwise (see below), which probably wasn't the best choice for
heat dissipation.
| | |
--- --- ---
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--- --- ---
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Thanks,
|
To get any credable answer you will have to tell us more about why you are
putting so many zeners in series and what you are trying to achieve with
this.
> Tim |
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Tam/WB2TT
Guest
|
| Posted:
Sat Feb 12, 2005 8:56 pm Post subject:
Re: Zener Heat |
|
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"Tim M" <tym1@spammenot.cwru.edu> wrote in message
news:cuk9dh$fmq$1@eeyore.INS.cwru.edu...
| Quote: | I'm designing a power supply that involves putting a bunch of zeners in
series, specifically 6 1N4742As (12V, 1W) and 12 1N4735As (6.2V, 1W). Yes,
I know that's a lot of zeners, but current drain of my circuit is only
40-50 mA. However, I notice the zeners getting very hot, even though I'm
well below the max power dissipation per diode.
What sort of heat sinking considerations should I be taking. The 1N4742As
are glass, the others metal. I have them laid out next to each other
lengthwise (see below), which probably wasn't the best choice for heat
dissipation.
| | |
--- --- ---
| | | | | |
--- --- ---
| | |
Thanks,
Tim
|
Why don't you make up a compound circuit using a TO3 power transistor and
fewer zeners. This way you can keep the zener current down to 1 ma, and bolt
the TO3 down to some heavy metal. What are your input and output voltages?
Tam |
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Tim M
Guest
|
| Posted:
Sat Feb 12, 2005 9:39 pm Post subject:
Re: Zener Heat |
|
|
I am using multiple diodes because I would like a reliable voltage drop
across a variety of currents, with the maximum being 50 mA and the
nominal current being much less, probably around 25 mA. I also need to
pull off multiple different supply voltages for different parts of my
circuit. I am powering multiple ICs (older TTL which draw more current)
some of which require eclcectic operating voltages.
My maximum current estimate is drawn from the summed maximum current
rating from all devices in the circuit.
With limited board space as well, I need to crowd the diodes together.
-Tim
Tam/WB2TT wrote:
| Quote: | "Tim M" <tym1@spammenot.cwru.edu> wrote in message
news:cuk9dh$fmq$1@eeyore.INS.cwru.edu...
I'm designing a power supply that involves putting a bunch of zeners in
series, specifically 6 1N4742As (12V, 1W) and 12 1N4735As (6.2V, 1W). Yes,
I know that's a lot of zeners, but current drain of my circuit is only
40-50 mA. However, I notice the zeners getting very hot, even though I'm
well below the max power dissipation per diode.
What sort of heat sinking considerations should I be taking. The 1N4742As
are glass, the others metal. I have them laid out next to each other
lengthwise (see below), which probably wasn't the best choice for heat
dissipation.
| | |
--- --- ---
| | | | | |
--- --- ---
| | |
Thanks,
Tim
Why don't you make up a compound circuit using a TO3 power transistor and
fewer zeners. This way you can keep the zener current down to 1 ma, and bolt
the TO3 down to some heavy metal. What are your input and output voltages?
Tam
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Fred Bloggs
Guest
|
| Posted:
Sat Feb 12, 2005 9:48 pm Post subject:
Re: Zener Heat |
|
|
| Quote: | I am using multiple diodes because I would like a reliable voltage drop
across a variety of currents, with the maximum being 50 mA and the
nominal current being much less, probably around 25 mA. I also need to
pull off multiple different supply voltages for different parts of my
circuit. I am powering multiple ICs (older TTL which draw more current)
some of which require eclcectic operating voltages.
My maximum current estimate is drawn from the summed maximum current
rating from all devices in the circuit.
|
That's not how zeners are used. Why don't you tell us what the
"eclectic" voltages are, referenced to common, and what is the loading
on each, what is the input voltage referenced to common. |
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Guest
|
| Posted:
Sat Feb 12, 2005 9:55 pm Post subject:
Re: Zener Heat |
|
|
i have used their milia treatment for milia seed on my eye brown area
and below cheek. after three applications, i noticed a reduction in the
milia size, quite impressed as i thought only laser surgery can solve
my problem.
--------------------------------
zest_f...@yahoo.com
i keep seeing reviews and raves about this
http://www.naturalisproducts.com and http://www.organiconline.com.sg .
many people are discussing in beauty forums and magazines have positive
reviews on this . but this thing ain't new, its been around for many
years! anyone tried can feedback to me on exactly how good it is?
----------------------------------------
can anyone help me please, am looking for the local distributor or any
shop selling the naturalis range of skin and body care products, from
this company http://www.naturalisproducts.com . looking for this
urgently. for those who have not come across it, its some foodbased
anti-aging products. i googled for this and received result showing its
available at http://www.organiconline.com.sg. i need this
urgently but shipping from singapore will take some time, if anyone is
distributing this please contact me at g...@raterenterprise.com
urgently. i have a group of us looking to buy this. thanks! |
|
| Back to top |
|
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Fred Bloggs
Guest
|
| Posted:
Sat Feb 12, 2005 10:04 pm Post subject:
Re: Zener Heat |
|
|
valiana@fastmail.fm wrote:
| Quote: | i have used their milia treatment for milia seed on my eye brown area
and below cheek. after three applications, i noticed a reduction in the
milia size, quite impressed as i thought only laser surgery can solve
my problem.
--------------------------------
zest_f...@yahoo.com
i keep seeing reviews and raves about this
http://www.naturalisproducts.com and http://www.organiconline.com.sg .
many people are discussing in beauty forums and magazines have positive
reviews on this . but this thing ain't new, its been around for many
years! anyone tried can feedback to me on exactly how good it is?
----------------------------------------
can anyone help me please, am looking for the local distributor or any
shop selling the naturalis range of skin and body care products, from
this company http://www.naturalisproducts.com . looking for this
urgently. for those who have not come across it, its some foodbased
anti-aging products. i googled for this and received result showing its
available at http://www.organiconline.com.sg. i need this
urgently but shipping from singapore will take some time, if anyone is
distributing this please contact me at g...@raterenterprise.com
urgently. i have a group of us looking to buy this. thanks!
|
That's makes about as much sense as anything else in this thread.... |
|
| Back to top |
|
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amdx
Guest
|
| Posted:
Sat Feb 12, 2005 10:21 pm Post subject:
Re: Zener Heat |
|
|
"Tim M" <tym1@spammenot.cwru.edu> wrote in message
news:cuk9dh$fmq$1@eeyore.INS.cwru.edu...
| Quote: | I'm designing a power supply that involves putting a bunch of zeners in
series, specifically 6 1N4742As (12V, 1W) and 12 1N4735As (6.2V, 1W).
|
Hi Tim,
Let's see if we can understand what you are doing.
1) Are the zeners in Series?
This would meaning you would have 98 volts at the top of the string.
2) What is the voltage you are feeding the string with ?
3) What is the value of your voltage dropping resistor?
If you could answer these three questions, then we can probably help.
Mike |
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John Fields
Guest
|
| Posted:
Sat Feb 12, 2005 10:49 pm Post subject:
Re: Zener Heat |
|
|
On Sat, 12 Feb 2005 16:04:08 GMT, Fred Bloggs <nospam@nospam.com>
wrote:
| Quote: |
valiana@fastmail.fm wrote:
i have used their milia treatment for milia seed on my eye brown area
and below cheek. after three applications, i noticed a reduction in the
milia size, quite impressed as i thought only laser surgery can solve
my problem.
--------------------------------
zest_f...@yahoo.com
i keep seeing reviews and raves about this
http://www.naturalisproducts.com and http://www.organiconline.com.sg .
many people are discussing in beauty forums and magazines have positive
reviews on this . but this thing ain't new, its been around for many
years! anyone tried can feedback to me on exactly how good it is?
----------------------------------------
can anyone help me please, am looking for the local distributor or any
shop selling the naturalis range of skin and body care products, from
this company http://www.naturalisproducts.com . looking for this
urgently. for those who have not come across it, its some foodbased
anti-aging products. i googled for this and received result showing its
available at http://www.organiconline.com.sg. i need this
urgently but shipping from singapore will take some time, if anyone is
distributing this please contact me at g...@raterenterprise.com
urgently. i have a group of us looking to buy this. thanks!
That's makes about as much sense as anything else in this thread....
|
---
Just some slimeball POS SPAMmer.
--
John Fields |
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|
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John Fields
Guest
|
| Posted:
Sat Feb 12, 2005 10:54 pm Post subject:
Re: Zener Heat |
|
|
On Sat, 12 Feb 2005 10:39:42 -0500, Tim M <tym1@spammenot.cwru.edu>
wrote:
| Quote: | I am using multiple diodes because I would like a reliable voltage drop
across a variety of currents, with the maximum being 50 mA and the
nominal current being much less, probably around 25 mA. I also need to
pull off multiple different supply voltages for different parts of my
circuit. I am powering multiple ICs (older TTL which draw more current)
some of which require eclcectic operating voltages.
|
---
If you're expecting a reliable series of voltage drops with different
currents going through the Zeners, you may well wind up being nastily
surprised, since the Zener voltages will only be guaranteed to be
within spec at a particular current (Izt, the Zener test current) and
all the errors will add up in the string and show up at the taps.
--
John Fields |
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John Popelish
Guest
|
| Posted:
Sun Feb 13, 2005 12:01 am Post subject:
Re: Zener Heat |
|
|
Tim M wrote:
| Quote: |
I was also thinking of making a (long) heat sink out of aluminum and
having it contact the package of each zener, probably with some heat
conductive paste in between. With the devices so closely spaced, there
isn't a lot of working room at the leads.
|
You will probably do better if you solder a small copper or brass shim
stock wing on each lead of the diodes right against the body. The
leads are the main conduit of heat out of the die. A pair if 1/4'
wide by 1" high wings can dump a lot of heat, compared to the diode
and ordinary circuit board pads.
--
John Popelish |
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