5 volt supply straight from 240v AC mains

On 2006-07-14, Byron A Jeff <byron@cc.gatech.edu> wrote:

>
> If you are determined, Microchip has a Technical Brief for a transformerless
> power supply. You can find it here:
>
> http://ww1.microchip.com/downloads/en/AppNotes/91008b.pdf
>
> This is dangerous. The brief says that it's dangerous. I'm telling you that
> this is dangerous and that you shouldn't do it. It's a safety hazard and a
> fire hazard and there's no good justification.
>
> My suggestion: DON'T DO IT!

I agree do not do it.

that fuse from neutral to earth may look harmless but it'll mess with any 
ELCB/RCD etc that the circuit is connected to, much better to leave the 
connection to earth off, at and treat the setup as what it is: a "live 
chassis", fusing the Live side probably makes more sense too.

Bye.
   Jasen

Tom Lucas vi=E1=BA=BFt :
> "techie_alison" <retro@dial.pipex.com> wrote in message
> news:n9CdnRSafcwThCvZnZ2dnUVZ8tCdnZ2d@bt.com...
> > Hi,
> >
> > Please may I ask what the arrangement is when you see a single LED
> > powered
> > straight off of a mains power supply without any transformers or
> > switch mode
> > circuitry?  In other words, totally uninsulated or regulated.
>
> I think you'll find that that is a neon lamp and not an LED. LED's
> connected directly across the mains will give light in the form of fire.
>
> > I have an old computer with an external hard disk which needs about 30
> > seconds to spin-up before the computer.  With a small timing circuit,
> > 555,
> > or using a PIC even (have dozens) after a set time a relay would be
> > set,
> > thus powering on the computer.  A 7805 could be introduced to take
> > into
> > account the voltage swing.  Half wave rectification could result in
> > 120v
> > too.
>
> Why not buy a 5V supply to run the electonics off rather than mess with
> mains yourself?
>
> > This doesn't need to be insulated from the outside world, safety is
> > not a
> > concern, just that roughly 5v should be available for the small
> > circuit and
> > the 3amp relay.
>
> SAFETY IS THE PRIMARY CONCERN! Mains is not something to be fooled with
> or it WILL kill you. Insulate everything or when you (or somebody else)
> is not at full concentration you will touch something and die. There
> should be fuses and other protection in the circuit as well. This is why
> you should seriously think about buying a supply and letting someone
> else handle the high voltage design - and the legal concerns that go
> with it.
>
> > Any ideas??  Just interested to hear of how this is done.  Or would it
> > be
> > easier to just buy a small tordial TX and make the box a bit bigger?
>
> If it were me then I would use 5V from the Hard drives supply to trigger
> a PIC (but a 555 or an RC circuit would be just as good) to control the
> PC's power switch. If the PC has an ATX supply, then great because you
> can stay low voltage and use a simple relay to replace the PC power
> switch (remembering that only a pulse is required to simulate a buton
> press). If the PC supply is AT then the power switch is mains and you
> could use a mains relay switched by 5V but you need to be sure that the
> terminals are properly insulated on the mains side.
>
> Seriously, your tone doesn't sound like you are giving mains electricity
> the respect it needs. I know enough people who have died from electric
> shocks and each time it was because they thought safety wasn't a
> concern. Be careful.

On 14 Jul 2006 11:15:00 -0400, byron@cc.gatech.edu (Byron A Jeff)
wrote:

>Unless you have a cost concern here, there's no justification for throwing 
>safety out the window. None whatsoever.

There's no question that a wall wart is safer than a non-isolated
supply, for some applications.  But this vociferous reaction about how
dangerous it is - is just not justified.

Many of us learned on vacuum tubes where the plate supply was an order
of magnitude more lethal than any mains voltage one might encounter.
Ever see the inside of a 100 KW transmitter power supply?  Build a
Tesla or Induction coil?  Rail Gun? Coil Gun? Vacuum tube amp or
transmitter?  Line regulator?  Repair a TV set? Power Factor
correction circuit? etc..

When all you need is a small indicator or circuit it makes sense to
use a cap to  drop voltage - more efficient than a wall wart, takes up
less space, less cost, lighter, no waste heat to speak of.  The
enclosure provides the shock protection.

For tinkering with circuits on a breadboard - or just learning
electronics, I'd agree it is too dangerous.  But the op mentions it
doesn't need to be isolated, so he probably already thought of using a
wall wart.

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On Sat, 15 Jul 2006 07:47:38 -0400, the renowned default
<none@nobody.net> wrote:
>
>For tinkering with circuits on a breadboard - or just learning
>electronics, I'd agree it is too dangerous.  But the op mentions it
>doesn't need to be isolated, so he probably already thought of using a
>wall wart.

IMHO, 99% of the time this topic comes up, it falls into the category
of "if you have to ask, don't use it". The 1% are mostly sensible
reliability and regulatory compliance concerns from people who do know
fairly well what they are doing. 


Best regards, 
Spehro Pefhany
-- 
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

On 14 Jul 2006 11:15:00 -0400, byron@cc.gatech.edu (Byron A Jeff)
wrote:

>In article <n9CdnRSafcwThCvZnZ2dnUVZ8tCdnZ2d@bt.com>,
>techie_alison <retro@dial.pipex.com> wrote:
>>Hi,
>
>>Please may I ask what the arrangement is when you see a single LED powered
>>straight off of a mains power supply without any transformers or switch mode
>>circuitry?  In other words, totally uninsulated or regulated.
>
>First off it's a dangerous one. A non isolated, non stepped down, non regulated
>circuit connected to 240V is a terrible accident waiting to happen.

At least in Europe, all tube televisions and many tube radios had a
universal (AC/DC) power supply, with a half wave rectifier generating
the B+ line about 200-250 V, thus there was only a rectifier between
the other mains plug terminal to the B+, while the other mains plug
terminal was directly connected to the metallic chassis. Depending on
the way the mains plug is inserted into the wall socket, you either
have the Neutral in the chassis or the full 220 Vac Live in the
chassis. Also the tube heaters were in series and across the Live and
Neutral, possibly with a VDR in series to limit the inrush current.

When working with such equipment I have used two main principles,
before starting to work, I _always_ checked the mains plug orientation
by measuring the metallic chassis voltage. When working with active
equipment, I put my left hand in the pocket and only work with my
right hand inside the equipment. This avoids the risk of having the
current flow through your heart. If you get a muscular cramp in your
right hand due to an electric shock, you still have the left hand
operational to cut the power.

Regarding low power devices powered by a series capacitor, I would
suggest using capacitors intended for mains filters. 

Instead of a single capacitor on the live side, put two in series,
each connecting one side to the respective mains plug terminal, while
the other terminal of each capacitor goes to the load (rectifier
etc.).  In this configuration, the small signal circuit is floating
around 110 Vac. If you accidentally touch the small signal circuit,
there is still the other capacitor in series between the mains voltage
and you, limiting the current through your body. If you want to limit
the worst case current to 30 mA, the normal circuit current
consumption must be below 10-15 mA, since in normal operation, there
are two capacitors in series.

Paul

"Paul Keinanen" <keinanen@sci.fi> wrote in message 
news:gtiib2h0ug41glernn7e732jiqaalvmk9b@4ax.com...
> On 14 Jul 2006 11:15:00 -0400, byron@cc.gatech.edu (Byron A Jeff)
> wrote:
>
>>In article <n9CdnRSafcwThCvZnZ2dnUVZ8tCdnZ2d@bt.com>,
>>techie_alison <retro@dial.pipex.com> wrote:
>>>Hi,
>>
>>>Please may I ask what the arrangement is when you see a single LED 
>>>powered
>>>straight off of a mains power supply without any transformers or switch 
>>>mode
>>>circuitry?  In other words, totally uninsulated or regulated.
>>
>>First off it's a dangerous one. A non isolated, non stepped down, non 
>>regulated
>>circuit connected to 240V is a terrible accident waiting to happen.
>
> At least in Europe, all tube televisions and many tube radios had a
> universal (AC/DC) power supply, with a half wave rectifier generating
> the B+ line about 200-250 V, thus there was only a rectifier between
> the other mains plug terminal to the B+, while the other mains plug
> terminal was directly connected to the metallic chassis. Depending on
> the way the mains plug is inserted into the wall socket, you either
> have the Neutral in the chassis or the full 220 Vac Live in the
> chassis. Also the tube heaters were in series and across the Live and
> Neutral, possibly with a VDR in series to limit the inrush current.
>
> When working with such equipment I have used two main principles,
> before starting to work, I _always_ checked the mains plug orientation
> by measuring the metallic chassis voltage. When working with active
> equipment, I put my left hand in the pocket and only work with my
> right hand inside the equipment. This avoids the risk of having the
> current flow through your heart. If you get a muscular cramp in your
> right hand due to an electric shock, you still have the left hand
> operational to cut the power.
>
> Regarding low power devices powered by a series capacitor, I would
> suggest using capacitors intended for mains filters.
>
> Instead of a single capacitor on the live side, put two in series,
> each connecting one side to the respective mains plug terminal, while
> the other terminal of each capacitor goes to the load (rectifier
> etc.).  In this configuration, the small signal circuit is floating
> around 110 Vac. If you accidentally touch the small signal circuit,
> there is still the other capacitor in series between the mains voltage
> and you, limiting the current through your body. If you want to limit
> the worst case current to 30 mA, the normal circuit current
> consumption must be below 10-15 mA, since in normal operation, there
> are two capacitors in series.
>
> Paul
>

This is a good idea because it also provides double protection against a 
capacitor short failure. Also due to the possibility of such a failure a 
series, low current fuse is advisable.

Dorian 

I agree.  I stuck a paper clip into a light switch when I was very young.  I 
am luck to be alive, or at least not brain damaged or anything like that.




"Tom Lucas" <news@REMOVEautoTOflameREPLY.clara.co.uk> wrote in message 
news:1152785669.50361.0@iris.uk.clara.net...
> "techie_alison" <retro@dial.pipex.com> wrote in message 
> news:n9CdnRSafcwThCvZnZ2dnUVZ8tCdnZ2d@bt.com...
>> Hi,
>>
>> Please may I ask what the arrangement is when you see a single LED 
>> powered
>> straight off of a mains power supply without any transformers or switch 
>> mode
>> circuitry?  In other words, totally uninsulated or regulated.
>
> I think you'll find that that is a neon lamp and not an LED. LED's 
> connected directly across the mains will give light in the form of fire.
>
>> I have an old computer with an external hard disk which needs about 30
>> seconds to spin-up before the computer.  With a small timing circuit, 
>> 555,
>> or using a PIC even (have dozens) after a set time a relay would be set,
>> thus powering on the computer.  A 7805 could be introduced to take into
>> account the voltage swing.  Half wave rectification could result in 120v
>> too.
>
> Why not buy a 5V supply to run the electonics off rather than mess with 
> mains yourself?
>
>> This doesn't need to be insulated from the outside world, safety is not a
>> concern, just that roughly 5v should be available for the small circuit 
>> and
>> the 3amp relay.
>
> SAFETY IS THE PRIMARY CONCERN! Mains is not something to be fooled with or 
> it WILL kill you. Insulate everything or when you (or somebody else) is 
> not at full concentration you will touch something and die. There should 
> be fuses and other protection in the circuit as well. This is why you 
> should seriously think about buying a supply and letting someone else 
> handle the high voltage design - and the legal concerns that go with it.
>
>> Any ideas??  Just interested to hear of how this is done.  Or would it be
>> easier to just buy a small tordial TX and make the box a bit bigger?
>
> If it were me then I would use 5V from the Hard drives supply to trigger a 
> PIC (but a 555 or an RC circuit would be just as good) to control the PC's 
> power switch. If the PC has an ATX supply, then great because you can stay 
> low voltage and use a simple relay to replace the PC power switch 
> (remembering that only a pulse is required to simulate a buton press). If 
> the PC supply is AT then the power switch is mains and you could use a 
> mains relay switched by 5V but you need to be sure that the terminals are 
> properly insulated on the mains side.
>
> Seriously, your tone doesn't sound like you are giving mains electricity 
> the respect it needs. I know enough people who have died from electric 
> shocks and each time it was because they thought safety wasn't a concern. 
> Be careful.
> 

On Sun, 16 Jul 2006 11:56:45 GMT, "���SHAD0W���"
<none@noemailaddress.nospam> wrote:

>I agree.  I stuck a paper clip into a light switch when I was very young.  I 
>am luck to be alive, or at least not brain damaged or anything like that.

---
Well, one out of two ain't bad... ;)


-- 
John Fields
Professional Circuit Designer 

In article <hckhb2l6fvnvibsv19cdmmp674a7c7tqs6@4ax.com>,
default  <none@nobody.net> wrote:
>On 14 Jul 2006 11:15:00 -0400, byron@cc.gatech.edu (Byron A Jeff)
>wrote:
>
>>Unless you have a cost concern here, there's no justification for throwing 
>>safety out the window. None whatsoever.

>There's no question that a wall wart is safer than a non-isolated
>supply, for some applications.  But this vociferous reaction about how
>dangerous it is - is just not justified.

Yes it is. Without isolation every part of that circuit should be considered
to be connected directly to the main, with the potential of upwards of 20A
of current at 240V potential. It can be lethal.

The OP came across an nonchanlant about the safety issue. That's the reason
for being vociferous.

>Many of us learned on vacuum tubes where the plate supply was an order
>of magnitude more lethal than any mains voltage one might encounter.

But I don't believe the OP was one of those folks. Anyone trained on
high voltage/high current equipment have a healthy respect for the safety
issues involved. The OP's apparent disregard for such safety issues is
what raised the alarm bells in my mind.

>Ever see the inside of a 100 KW transmitter power supply?  Build a
>Tesla or Induction coil?  Rail Gun? Coil Gun? Vacuum tube amp or
>transmitter?  Line regulator?  Repair a TV set? Power Factor
>correction circuit? etc..

No. Each are potentially lethal and have specific safety procedures
for building, using, and servicing such equipment. Right?

Can we at least agree that the attitude inside such equipment should not
be "no big deal"?

>When all you need is a small indicator or circuit it makes sense to
>use a cap to  drop voltage - more efficient than a wall wart, takes up
>less space, less cost, lighter, no waste heat to speak of.  The
>enclosure provides the shock protection.

Several issues here:

1) The OP wanted to drive a relay. It isn't clear that the cap can provide 
enough current to drive it.

2) The enclosure is the only isolation. Everything inside that case needs
to be considered to be at line potential.

3) The OP said he wasn't concerned about safety issues.

>For tinkering with circuits on a breadboard - or just learning
>electronics, I'd agree it is too dangerous.  But the op mentions it
>doesn't need to be isolated, so he probably already thought of using a
>wall wart.

The only point I got from the discussion was that he was concerned about
the size of he circuit.

BAJ

Byron A Jeff wrote:
> 
>>There's no question that a wall wart is safer than a non-isolated
>>supply, for some applications.  But this vociferous reaction about how
>>dangerous it is - is just not justified.
> 
> Yes it is. Without isolation every part of that circuit should be considered
> to be connected directly to the main, with the potential of upwards of 20A
> of current at 240V potential. It can be lethal.

I'm with Paul Keinanen on this one; thousands of devices in past
and current use derive power through reactive coupling directly to the
mains and in the U.S. have been and are U.L. approved.
> 
> The OP came across as nonchanlant about the safety issue. That's the reason
> for being vociferous.

What linguistic features of the original post lead you to believe that?
> 
> 
>>Many of us learned on vacuum tubes where the plate supply was an order
>>of magnitude more lethal than any mains voltage one might encounter.
> 
> 
> But I don't believe the OP was one of those folks. Anyone trained on
> high voltage/high current equipment have a healthy respect for the safety
> issues involved. The OP's apparent disregard for such safety issues is
> what raised the alarm bells in my mind.

Again, if you have followed Alison's posts I don't really believe you
can draw that conclusion, it appears that she has a lot of experience
and sagacity.
> 
> 
>>Ever see the inside of a 100 KW transmitter power supply?  Build a
>>Tesla or Induction coil?  Rail Gun? Coil Gun? Vacuum tube amp or
>>transmitter?  Line regulator?  Repair a TV set? Power Factor
>>correction circuit? etc..
> 
> 
> No. Each are potentially lethal and have specific safety procedures
> for building, using, and servicing such equipment. Right?

Right, and every Boy Scout troop in the 1960s built or experimented
with such things.

> 
> Can we at least agree that the attitude inside such equipment should not
> be "no big deal"?

Just common application of 'best practices' that _anyone_ working with
electronics should possess.

> 3) The OP said he wasn't concerned about safety issues.
> 

Alison is best probably referenced as 'she'. Give her the benefit of the
doubt when parsing that sentence; I suspect she implied that this is not
something for external consumption or approval and that she has
the intent to maintain safety within her internal environment.

Her original idea, to derive +5V without switch-mode circuitry is
a clever one and as has been demonstrated by this thread eminently
do-able, however I feel that the real-estate used by the discrete parts
(including zener regulation) would not be significantly increased by
the addition of a switching regulator, which would make the design more 
robust.

Regards,

Michael