LED Driver
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I want to drive several hundred leds (2.0V, 20ma per) from a stamp. This
question is indirectly related to the stamp as I have a working stamp
interface.
The LED's will all come on and off at the same time.
What is the best way to drive this many LED's? Do they need to be subgrouped
with subgroup current regulation? How many can be combined in a parallel or
series array? Is there any significant advantage between serial and parallel
arrays?
Thanks,
Scott
[noparse][[/noparse]Non-text portions of this message have been removed]
question is indirectly related to the stamp as I have a working stamp
interface.
The LED's will all come on and off at the same time.
What is the best way to drive this many LED's? Do they need to be subgrouped
with subgroup current regulation? How many can be combined in a parallel or
series array? Is there any significant advantage between serial and parallel
arrays?
Thanks,
Scott
[noparse][[/noparse]Non-text portions of this message have been removed]
Comments
>I want to drive several hundred leds (2.0V, 20ma per) from a stamp. This
>question is indirectly related to the stamp as I have a working stamp
>interface.
>
>The LED's will all come on and off at the same time.
What kind of safety concerns are there? What are the consequences of
several LEDs failing to operate?
If the LEDs can be adequately protected from inquisitive fingers and if a
group of LEDs that goes dark because of a defective LED that fails open
(rare - most LEDs fail short) is not a major problem, I'd seriously
consider using a relay or SSR to switch raw AC power to series
strings. You will still need a current regulator for each string but the
compliance voltage range can be limited so that you can use inexpensive
components. A LM317HV is good for 60V - if you arrange the series strings
so that they drop about 120V DC, a LM317HV configured as a constant current
source will have about 30V dropped across it. Use a bridge rectifier to
feed the whole string (no filter cap except for a 0.1 uF cap at the input
of the LM317HV).
The string will pulse at twice the line frequency much like a fluorescent
tube - is that a problem?
dwayne
Dwayne Reid <dwayner@p...>
Trinity Electronics Systems Ltd Edmonton, AB, CANADA
(780) 489-3199 voice (780) 487-6397 fax
Celebrating 18 years of Engineering Innovation (1984 - 2002)
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dwayner@p... writes:
> At 04:53 AM 4/22/02 -0400, scottsmith13@a... wrote:
> >I want to drive several hundred leds (2.0V, 20ma per) from a stamp. This
> >question is indirectly related to the stamp as I have a working stamp
> >interface.
> >
> >The LED's will all come on and off at the same time.
>
> What kind of safety concerns are there?
What are the consequences of > several LEDs failing to operate?
>
A bit more background on the project: the LED's are being used as a visual
signal on a motorvehicle; specifically a Ford F-350 that is being used for
rescue work. The truck has a standard 12v system. Once the LED array is made,
it will be semi-permanently sealed under a clear cover. While failure of a
few LED's will not be catastrophic, I would like to minimize the effects of
failure while still being realistic with the number of components. My current
concept is to use one main voltage regulator to feed current limiting
resistors on each array. Reasonable? Something better?
> If the LEDs can be adequately protected from inquisitive fingers and if a
> group of LEDs that goes dark because of a defective LED that fails open
> (rare - most LEDs fail short) is not a major problem, I'd seriously
> consider using a relay or SSR to switch raw AC power to series
> strings. You will still need a current regulator for each string but the
>
[noparse][[/noparse]Non-text portions of this message have been removed]
>A bit more background on the project: the LED's are being used as a visual
>signal on a motorvehicle; specifically a Ford F-350 that is being used for
>rescue work. The truck has a standard 12v system. Once the LED array is made,
>it will be semi-permanently sealed under a clear cover. While failure of a
>few LED's will not be catastrophic, I would like to minimize the effects of
>failure while still being realistic with the number of components. My current
>concept is to use one main voltage regulator to feed current limiting
>resistors on each array. Reasonable? Something better?
Easy! Don't bother with regulators - just put somewhere between 4 & 6 LEDs
in series with a resistor selected to give you the desired current while
the engine is idling - figure about 13.5 Vdc. If you were making many of
these, I'd consider using boost regulators with a couple of dozen LEDs in
series in each string but I suspect that will be more effort that you want
to put in.
dwayne
Dwayne Reid <dwayner@p...>
Trinity Electronics Systems Ltd Edmonton, AB, CANADA
(780) 489-3199 voice (780) 487-6397 fax
Celebrating 18 years of Engineering Innovation (1984 - 2002)
.-. .-. .-. .-. .-. .-. .-. .-. .-. .-
`-' `-' `-' `-' `-' `-' `-' `-' `-'
Do NOT send unsolicited commercial email to this email address.
This message neither grants consent to receive unsolicited
commercial email nor is intended to solicit commercial email.