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Pig Bladder
Guest
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 Posted:
Sun Feb 13, 2005 6:11 am Post subject:
Re: Zener Heat |
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On Sat, 12 Feb 2005 16:04:08 +0000, Fred Bloggs wrote:
| Quote: |
valiana@fastmail.fm wrote:
i have used their milia treatment for milia seed on my eye brown area
....
That's makes about as much sense as anything else in this thread....
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Never argue with a bot. People might not be able to tell the difference.
--
The Pig Bladder From Uranus, Still Waiting for
Some Hot Babe to Ask What My Favorite Planet Is.
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Rich Grise
Guest
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| Posted:
Sun Feb 13, 2005 6:11 am Post subject:
Re: Zener Heat |
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On Sat, 12 Feb 2005 16:29:17 -0500, Tim M wrote:
| Quote: | Well, the project is for a Nixie clock, and I'm using a Villard voltage
doubler and line current to power the tubes, as 1.414*110 V is below the
required ionization voltage. To keep things simple, I'm tapping across
one of the capacitors that only sees 1.414*110 V and using the Zeners to
drop the voltage to a low enough level for a 5V voltage regulator.
Some of the old TTL chips used in my desgin require a relatively high
current (e.g. up to 25 mA for the 7441, though I will be using its
output to switch transistors as opposed to driving the Nixies directly,
so I expect to be well below this).
I've been a bit incomplete about the rest because I haven't finished
designing the logic and tube driver stages and haven't nailed down exact
parameters beyond a maximum current drain specification.
I'm quite aware of the dangers of high voltage--line AC especially--but
thank you for the reminder.
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Feed the nixie anodes with half-wave of full-wave rectified, unfiltered,
pulsating DC, through about a 100K resistor. You don't need to regulate
that. Run the collectors of your driver transistors pulled up through,
maybe, 22K to about 20V. Whichever transistor you turn on will connect
that cathode to ground, the nixie strikes, and none of the transistors
has to withstand more than 20V.
At least I read an article once that said something like that. I've also
seen stuff driven with SCRs, with half- or full-wave rectifiec AC on the
other side of the load.
Good Luck!
Rich |
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Fred Bloggs
Guest
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| Posted:
Sun Feb 13, 2005 6:11 am Post subject:
Re: Zener Heat |
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| Quote: | Well, the project is for a Nixie clock, and I'm using a Villard voltage
doubler and line current to power the tubes, as 1.414*110 V is below the
required ionization voltage. To keep things simple, I'm tapping across
one of the capacitors that only sees 1.414*110 V and using the Zeners to
drop the voltage to a low enough level for a 5V voltage regulator.
Some of the old TTL chips used in my desgin require a relatively high
current (e.g. up to 25 mA for the 7441, though I will be using its
output to switch transistors as opposed to driving the Nixies directly,
so I expect to be well below this).
|
You need to get rid of the zeners and put that power dissipation in a
component built to take it, like a power resistor, and you can parallel
two 6.2V zeners so as to cut their temperature rise by half with Tj at a
maximum of 22oC above ambient. None of the semiconductors get warm:
View in a fixed-width font such as Courier.
.
.
.
. 2.7K 20W
. HV---/\/\--------+--------------.
. | 1N4001 |
. --|>|----. |
. | |
. +---------+ |
. | | |
. |1N4735's | |
. | | |
. ---/ ---/ |
. // \ // \ | 7805
. --- --- | +-------+
. | | +----+--|IN OUT|---+----+-->
. | |/ | | | | | |
. ,-----+-------| T1 |+ | | | | |+
. | | |\e === === | GND | === ===
. | \| | | | +-------+ | |
. 470 T2 |-------+ 10U 0.1U | 0.1U 10U
. | e/| | | | | | |
. | | 27 | | | | |
. COM-------+-----+---------+----+----+------+-------+----+-->
.
. 2N2922's
.
.
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Rich Grise
Guest
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| Posted:
Sun Feb 13, 2005 6:11 am Post subject:
Re: Zener Heat |
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On Sat, 12 Feb 2005 17:21:26 -0500, Tim M wrote:
| Quote: | Actually, I think it should be 36 mA and not 3.6 mA.
I wish to do thing sans transformers for size and weight issues, plus I
don't want the finished project to require two separate electrical outlets.
The complete power supply circuit works under 36 mA load except for the
heating of the zeners.
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Well, since the thing's already a death trap, you might as well use the
capacitor-diode-zener trick. Just run a half-wave doubler by way of a
capacitor to the hot side of the mains. Filter and zener the output of
that. Size the series capacitor to get your load current into spec, and of
course you can filter it to your heart's content. ;-)
Have Fun!
Rich |
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kell
Guest
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| Posted:
Sun Feb 13, 2005 6:11 am Post subject:
Re: Zener Heat |
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You don't have to use a zener string to drop all that voltage.
There is another way to make a low voltage power supply from
line power without using a transformer, if you only need a few
dozen milliamps.
Take a full bridge (four diodes). Feed it from the mains
through a series capacitor. The capacitor's impedance will limit
current into the bridge. You can filter the bridge's output and
regulate it with a zener, since you will have limited current.
The current out of the bridge will be directly proportional to
the capacitance of your blocking capacitor. For 50 mA you would
need something like 1 uF. So with no load your 5 volt zener
conducting 50 mA would dissipate .25 watts, very doable.
You might want to have a resistor in there in addition to the
capacitor, to alleviate possible inrush problems. |
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Tim M
Guest
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| Posted:
Sun Feb 13, 2005 6:11 am Post subject:
Re: Zener Heat |
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All of these things are from suggestions in this thread and not my
"foolish" idea, sir. I don't see you hassling them.
-Tim
Fred Bloggs wrote:
| Quote: |
Adding copper fins to the leads of the zeners does dissipate heat
nicely so that the temperature is within spec,
Wonderful- nothing like lots of exposed metal at high ungrounded voltage.
but I agree that this design is a bit flaky for continuous use.
I will give the doubler-capacitor and capacitor-rectifier tricks a
try. Will have to see what I have in the parts bin.
That's even more foolish than your original idea.
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Tim M
Guest
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| Posted:
Sun Feb 13, 2005 12:09 pm Post subject:
Re: Zener Heat |
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Thanks for taking the 3 minutes! This is a handy pdf.
The Zener string works and doesn't overheat, but what you've dug up is
definitely better.
Oh well, at least I know I will have enough Zeners around for building
this circuit!
-Tim
Rich Grise wrote:
| Quote: | On Sun, 13 Feb 2005 01:55:49 +0000, Fred Bloggs wrote:
Adding copper fins to the leads of the zeners does dissipate heat nicely
so that the temperature is within spec,
Wonderful- nothing like lots of exposed metal at high ungrounded voltage.
but I agree that this design is
a bit flaky for continuous use.
I will give the doubler-capacitor and capacitor-rectifier tricks a try.
Will have to see what I have in the parts bin.
That's even more foolish than your original idea.
Bloggs, don't be an idiot.
It is _not_ "more" foolish. In fact, I'd argue that it's not _as_ foolish.
But I use the logic that, since he already has an unisolated 170V supply,
the addition of a couple of capacitors and a couple of diodes and ONE
zener (depending on what voltage he actually wants) gets rid of the hot
exposed string, reduces the current requirements of the 170V supply almost
a hundredfold, and - well, if that's not enough, then oh well.
Oh, yeah. It gives him the LV supply at arbitrary current, if he's clever
enough to copy the design properly:
http://ww1.microchip.com/downloads/en/AppNotes/00954A.pdf
(three minute google search) ;-p
Thanks,
Rich
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Ken Moffett
Guest
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| Posted:
Sun Feb 13, 2005 5:30 pm Post subject:
Re: Zener Heat |
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Tim M wrote:
| Quote: |
Actually, I think it should be 36 mA and not 3.6 mA.
I wish to do thing sans transformers for size and weight issues, plus I
don't want the finished project to require two separate electrical outlets.
The complete power supply circuit works under 36 mA load except for the
heating of the zeners.
-Tim
John Woodgate wrote:
I read in sci.electronics.design that Tim M <tym1@spammenot.cwru.edu
wrote (in <culsfj$rf6$1@eeyore.INS.cwru.edu>) about 'Zener Heat', on
Sat, 12 Feb 2005:
To keep things simple, I'm tapping across
one of the capacitors that only sees 1.414*110 V and using the Zeners to
drop the voltage to a low enough level for a 5V voltage regulator.
This is not a good design. You would do far better to derive your 5 V
supply from a 9 V wall-wart.
If you are putting the zener string in series with your regulator, it
simply won't work, nor will it work if you put the regulator across a 12
V zener at the ground end of the string. Your zener current of 3.6 mA is
the maximum you can draw from the regulator.
|
When I don't want two power cords, what I've done is carefully saw open a small (<100mA)
wall-wart and mount the transformer and rectifier/filter PCB inside my project. Without the
plastic case the small ones have a very small footprint, actually no bigger than the
non-isolated series capacitor/zener supply that has been mentioned.
And, on the subject of gutting wall-warts, keep your eye out for the SMPS types. At
Goodwill/Savers/ARC stores you can spot them because they're extremely light for their V/A
rating (ie 5v@1.5A in a couple of ounces), compared to the laminated-iron transformer
versions. The ones I've found use standard SMPS chips. With the data sheet from the
chip manufacturer, I've been able to replace one or two of the ouput programming resistors,
and set whatever voltage I need. Small, light, isolated, adjustable, and all for $0.99 plus
tax. |
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R.Lewis
Guest
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| Posted:
Sun Feb 13, 2005 6:36 pm Post subject:
Re: Zener Heat |
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"Rich Grise" <richgrise@example.net> wrote in message
news:pan.2005.02.13.05.49.34.854148@example.net...
| Quote: | On Sun, 13 Feb 2005 01:55:49 +0000, Fred Bloggs wrote:
Adding copper fins to the leads of the zeners does dissipate heat
nicely
so that the temperature is within spec,
Wonderful- nothing like lots of exposed metal at high ungrounded
voltage.
but I agree that this design is
a bit flaky for continuous use.
I will give the doubler-capacitor and capacitor-rectifier tricks a try.
Will have to see what I have in the parts bin.
That's even more foolish than your original idea.
Bloggs, don't be an idiot.
It is _not_ "more" foolish. In fact, I'd argue that it's not _as_ foolish.
But I use the logic that, since he already has an unisolated 170V supply,
the addition of a couple of capacitors and a couple of diodes and ONE
zener (depending on what voltage he actually wants) gets rid of the hot
exposed string, reduces the current requirements of the 170V supply almost
a hundredfold, and - well, if that's not enough, then oh well.
Oh, yeah. It gives him the LV supply at arbitrary current, if he's clever
enough to copy the design properly:
http://ww1.microchip.com/downloads/en/AppNotes/00954A.pdf
(three minute google search) ;-p
Thanks,
Rich
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Rich
There is a fellow here that seems almost intent on self harm by way of
electrocution.
Suggesting a reactive dropper will only make him think that it is 'safe'
because now the volts is low - clamped by the zener - and goodness knows
where that will lead him.
Dear sir,
Use a wall wart: Use a wall wart: Use a wall wart: Use a wall wart:
Use a wall wart: Use a wall wart: Use a wall wart: Use a wall wart:
You will probably never get this thing to work but at least you will be
alive to recount the tale.
regards,
me |
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amdx
Guest
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| Posted:
Sun Feb 13, 2005 6:49 pm Post subject:
Re: Zener Heat |
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| Quote: |
Well, since the thing's already a death trap, you might as well use the
capacitor-diode-zener trick. Just run a half-wave doubler by way of a
capacitor to the hot side of the mains. Filter and zener the output of
that. Size the series capacitor to get your load current into spec, and of
course you can filter it to your heart's content. ;-)
|
You can make it safer by using two identical transformers
back to back such as this;
pri-TRANSFORMER-sec=sec TRANSFORMER-pri
this way you get isolation and still have your 155v or 170v output.
Mike |
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John Smith
Guest
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| Posted:
Sun Feb 13, 2005 9:48 pm Post subject:
Re: Zener Heat |
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"kell" <kellrobinson@billburg.com> wrote in message
news:1108253542.157574.30460@c13g2000cwb.googlegroups.com...
| Quote: | You don't have to use a zener string to drop all that voltage.
There is another way to make a low voltage power supply from
line power without using a transformer, if you only need a few
dozen milliamps.
Take a full bridge (four diodes). Feed it from the mains
through a series capacitor. The capacitor's impedance will limit
current into the bridge. You can filter the bridge's output and
regulate it with a zener, since you will have limited current.
The current out of the bridge will be directly proportional to
the capacitance of your blocking capacitor. For 50 mA you would
need something like 1 uF. So with no load your 5 volt zener
conducting 50 mA would dissipate .25 watts, very doable.
You might want to have a resistor in there in addition to the
capacitor, to alleviate possible inrush problems.
|
In addition, you should follow the resistor with a transient suppressor.
J |
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Fred Bloggs
Guest
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| Posted:
Mon Feb 14, 2005 1:42 am Post subject:
Re: Zener Heat |
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John Smith wrote:
| Quote: | In addition, you should follow the resistor with a transient suppressor.
|
That's the problem with the series line capacitor method which is
incomprehensible and misused by nearly every hack and hobbyist who ever
used it. A transformerless power supply that is perfectly safe when
double insulated would be something this- cheap small 1.5ARMS ripple
e-caps will work well, and line transient suppression follows naturally:
View in a fixed-width font such as Courier.
.
. 1.5A
. 600PIV
. fuse --FWB---
. o-~--|~ +|------+-----> HV to anodes
. | | |+
.LINE | -|>|- | |250V
. | -|-. ===
. o--+-|~ | | 100u
. | -------- | | 20W
. | | | 2.7K
. '------------|----+---/\/\-+----------------+-----+
. | | | | |
. | | '-|>|-|>|-. | |
. | | | | |
. | | +-+--+ | |
. | | | | |+ |
. | | 2x - - |16V 7805->5V
. | | 1N4735A-> ^ ^ === |
. | |+ - - 470u |
. | |250V | | | |
. | === / / | |
. | 100u 12 \ 12 \ | |
. | | | | | |
. | | | | | |
. '----+----------------+----+---+-----+-->com
.
.
.
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.
. |
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Fred Bloggs
Guest
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| Posted:
Mon Feb 14, 2005 1:45 am Post subject:
Re: Zener Heat |
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Fred Bloggs wrote:
[..snip wrong diagram..]
View in a fixed-width font such as Courier.
.
. 1.5A
. 600PIV
. fuse --FWB---
.o-~----|~ +|------+-----> HV to anodes
. | | |+
.LINE | -|>|- | |250V
. | -|-. ===
.o-~--+-|~ | | 100u
. fuse| -------- | | 20W
. | | | 2.7K
. '------------|----+---/\/\-+----------------+-----+
. | | | 2x 1N4001 | |
. | | '-|>|-|>|-. | |
. | | | | |
. | | +-+--+ | |
. | | | | |+ |
. | | 2x - - |16V 7805->5V
. | | 1N4735A-> ^ ^ === |
. | |+ - - 470u |
. | |250V | | | |
. | === / / | |
. | 100u 12 \ 12 \ | |
. | | | | | |
. | | | | | |
. '----+----------------+----+---+-----+-->com
.
.
.
.
.
.
. |
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kell
Guest
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| Posted:
Mon Feb 14, 2005 5:04 am Post subject:
Re: Zener Heat |
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| So the series line capacitor is a no-no? |
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R.Lewis
Guest
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| Posted:
Mon Feb 14, 2005 5:15 am Post subject:
Re: Zener Heat |
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"kell" <kellrobinson@billburg.com> wrote in message
news:1108333498.198539.185420@c13g2000cwb.googlegroups.com...
| Quote: | So the series line capacitor is a no-no?
Only if you need to be told why there is a resistor in series with the |
capacitor, why there is one in parallel with the capacitor, why a transient
suppressor is necessary, what is the difference between X and Y rated
capacitors, and what class ll means.
Otherwise there are millions of successful products out there with reactive
ballasts. |
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