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'[EE] 230vAC powered, CC LED drivers?'
2010\07\28@110524 by Matt Rhys-Roberts

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 On 28/07/2010 13:15, Xiaofan Chen wrote:
> Do you mean constant current?
>
Yes, you're right. Subject changed appropriately.

I wish to buy (or will need to design) the smallest and most efficient constant current ballast that directly takes 230vAC UK mains (6% deltaV, 50Hz), to supply 40mA to a power LED string with a voltage drop of 216v. I'm only just starting to play with LED lighting and don't wish to re-invent too many wheels.
> Not sure if Suptertex has something you can use. They
> seems to have quite some good things related to high
> voltage ICs.
> http://www.supertex.com/
Their HV9918 looks interesting, but only takes up to 40v. I wonder if I'm asking too much to find a ready made brick that achieves the above?

Mat

2010\07\28@113600 by RussellMc

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> I wish to buy (or will need to design) the smallest and most efficient
> constant current ballast that directly takes 230vAC UK mains (6% deltaV,
> 50Hz), to supply 40mA to a power LED string with a voltage drop of 216v.

There may be a few more issues. Depending on volume and application,
powrr factor may be an issue. If you are working from steady DC
without any preprocessing from AC to DC then you'll end up with around
1.4 x 230 = 300+ VDC and you'll have to buck from there. You MAY wish
to phase controlled rectify, when power factor may become an issue.

Gargoyling eg offline LED driver produces many ideas.
eg

Phase controlled Power Factor correcting TRIAC systems
A large number of app notes - some highl;y relevant

                http://www.powerint.com/applications/led-lighting

eg Far far far too complex - but gives some ideas:

          http://www.powerint.com/sites/default/files/PDFFiles/di130.pdf

Equally nasty

        http://www.powerint.com/sites/default/files/PDFFiles/der167.pdf

This is more like it.
Most unusual.

      http://www.powerint.com/sites/default/files/PDFFiles/di92.pdf

Another

              http://www.powerint.com/sites/default/files/PDFFiles/di92.pdf



LEDs magazine - specific comments here and also much else relevcant in
ongoingf dfree magazines

         http://www.ledsmagazine.com/features/5/4/9


http://www.maxim-ic.com/app-notes/index.mvp/id/4387

This may be useful
http://www.national.com/cat/index.cgi?i=i//22

2010\07\28@120852 by alan.b.pearce

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> > I wish to buy (or will need to design) the smallest and most
efficient
> > constant current ballast that directly takes 230vAC UK mains (6%
deltaV,
> > 50Hz), to supply 40mA to a power LED string with a voltage drop of
216v.
>
> There may be a few more issues. Depending on volume and application,
> powrr factor may be an issue. If you are working from steady DC
> without any preprocessing from AC to DC then you'll end up with around
> 1.4 x 230 = 300+ VDC and you'll have to buck from there. You MAY wish
> to phase controlled rectify, when power factor may become an issue.

ST make off-line SMPS chips, some designed for use in wall-wart devices.
They also have a good range of app notes to cover them.

http://www.st.com/stonline/

Under Power Modules they have a single power brick that may suit.

Under Power Management they have a whole range of chips (look at the
Viper range) as well as PFC control chips.
-- Scanned by iCritical.

2010\07\28@123941 by Dwayne Reid

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At 09:02 AM 7/28/2010, Matt Rhys-Roberts wrote:

>I wish to buy (or will need to design) the smallest and most efficient
>constant current ballast that directly takes 230vAC UK mains (6% deltaV,
>50Hz), to supply 40mA to a power LED string with a voltage drop of 216v.

Gosh - that requirement changes things significantly.  It probably just got easier.

I have been purchasing small LED lamps that operate from 120Vac.  They consist of 20 white LEDs in series for a total voltage drop of near 64 Vdc.  The package states that each lamp consumes about 1.5W and I find that they put out somewhat less light than the 40W bulb they are replacing.  The fixture holds 3 lamps and I find the light output to be completely adequate (they are hall lights in my house).  I'm thrilled to have those fixtures consume 4.5W instead of the 120W they used to eat up - my wife tends to leave those fixtures (several) turned on whenever she is home.

The power supply is the ubiquitous capacitive-type current limiter: a series capacitor and small series resistor that feeds a bridge rectifier, then to a smallish filter cap, another small series resistor, then the LED string.  I could go look up the specific values if you wish - I sketched the schematic before reassembling the lamp I took apart.

It works well.  There is NO visible flicker (and my eyes are extremely sensitive to flicker) and the LEDs continue to glow dimly for several seconds after power is removed.  I have no idea if that glow is due to the charge stored in the filter cap or if its phosphor decay time - or both.

Why not spend a few minutes with your calculator (or LTspice from Linear Technology) to see what capacitor value you need to give you 40mA with a 50V or so drop at 50Hz.  You might be surprised at how small (physically) that capacitor is.

dwayne

-- Dwayne Reid   <spam_OUTdwaynerTakeThisOuTspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax
http://www.trinity-electronics.com
Custom Electronics Design and Manufacturing

2010\07\29@103023 by Matt Rhys-Roberts

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 On 28/07/2010 17:39, Dwayne Reid wrote:
> ubiquitous capacitive-type current limiter
Aha, this seems to be the ticket.
Just got to make sure I've understood the power theory thoroughly enough in both real and imaginary terms, then to add a bleeder resistor for safety, then finally write an on-line component calculator for people as lazy as me!
Thanks,
Mat

2010\07\29@121905 by RussellMc

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>> ubiquitous capacitive-type current limiter ...

I know you know BUT such circuits must be treated as if they have live
mains at all points at all times - as they can have.
Fully protected against intrusion is a minimum and graphically
labelled for the unknown future repairer is good.
Perhaps may not meet regulatory requirements in some cases?


   Russel

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