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Flashing LED circuit

N

nick

Jan 1, 1970
0
Dear All,

Please can you advise on the wiring of a flashing LED circuit.

I want to connect 5 off 10mm red flashing HE LEDs (RS no.262-2977
Kingbright no.L-816BID) to a 9v DC supply.

It says on their spec sheet:

VF 9-12v
IF 22mA
IF max 38-56mA
Power dissipation 310mW
VR max 0.5v

Should I wire them in parallel?

I believe I cannot wire them in series as the voltage drop across each
LED will be too much for the supply won't it?

It says in the catalogue that series resistors are not required and
cannot be used to drop a higher voltage.

Any advice will be gratefully received!
 
J

John Fields

Jan 1, 1970
0
Dear All,

Please can you advise on the wiring of a flashing LED circuit.

I want to connect 5 off 10mm red flashing HE LEDs (RS no.262-2977
Kingbright no.L-816BID) to a 9v DC supply.

It says on their spec sheet:

VF 9-12v
IF 22mA
IF max 38-56mA
Power dissipation 310mW
VR max 0.5v

Should I wire them in parallel?
 
M

Mark VB

Jan 1, 1970
0
nick said:
Dear All,

Please can you advise on the wiring of a flashing LED circuit.

I want to connect 5 off 10mm red flashing HE LEDs (RS no.262-2977
Kingbright no.L-816BID) to a 9v DC supply.

It says on their spec sheet:

VF 9-12v
IF 22mA
IF max 38-56mA
Power dissipation 310mW
VR max 0.5v

Should I wire them in parallel?

I believe I cannot wire them in series as the voltage drop across each
LED will be too much for the supply won't it?

It says in the catalogue that series resistors are not required and
cannot be used to drop a higher voltage.

Any advice will be gratefully received!

It seems that your LEDs have built-in current-control. So wiring them
in parallel should do.


HTH,
Mark Van Borm
 
N

nick

Jan 1, 1970
0
Mark said:
It seems that your LEDs have built-in current-control. So wiring them
in parallel should do.


HTH,
Mark Van Borm


Thanks for your advice guys!

I was asking these questions because having constructed a few of these
circuits in parallel arrangements for use at work, some of them have
packed up completely. Presumably one LED blew and caused the others to
blow.

Is there any way I can prevent this from happening again? Adding a
resistor to each LED? If so what size would you recommend?

Thanks in advance for your help!
 
N

Nelson Johnsrud

Jan 1, 1970
0
nick said:
Thanks for your advice guys!

I was asking these questions because having constructed a few of these
circuits in parallel arrangements for use at work, some of them have
packed up completely. Presumably one LED blew and caused the others to
blow.

Is there any way I can prevent this from happening again? Adding a
resistor to each LED? If so what size would you recommend?

Thanks in advance for your help!
Generally, each LED should have a resistor in series to limit the
current through the LED. You will have to look at the spec. sheet for
your particular LED, but most are looking for 2-3V and 20 mA operating
current. The size of the resistor depends on supply voltage, and will
have to be calculated accordingly. Paralleling LED's is not a good idea
without a series restor on each LED.

Nels
 
M

Mark VB

Jan 1, 1970
0
nick said:
I was asking these questions because having constructed a few of these
circuits in parallel arrangements for use at work, some of them have
packed up completely. Presumably one LED blew and caused the others to
blow.

Is there any way I can prevent this from happening again? Adding a
resistor to each LED? If so what size would you recommend?

Thanks in advance for your help!

Probably, the polarity was reversed when they blew, so adding a resistor
won't help much.


Mark VB
 
R

Rich Grise

Jan 1, 1970
0
Thanks for your advice guys!

I was asking these questions because having constructed a few of these
circuits in parallel arrangements for use at work, some of them have
packed up completely. Presumably one LED blew and caused the others to
blow.

This is probably not the mechanism. The LEDs in your original post
DO NOT need a series dropping resistor. I'm guessing that you used
ordinary LEDs in parallel, with only one dropping resistor. This
will NOT work, because they have different forward voltage drops
and one will hog all of the current until it blows, and then you
get a cascade effect as the rest of the LEDs are overdriven by
the lower-value resistor.
Is there any way I can prevent this from happening again? Adding a
resistor to each LED? If so what size would you recommend?

THESE LEDS:
do NOT need any resistor - in fact, you said yourself that the spec
sheet specifically says not to use one.

Any other "standard" LED DOES need a series resistor, because when
the forward voltage reaches 1.2V (or whatever the Vf), there is
no mechanism to limit the LED's current other than the series resistor.
This might be helpful:
http://focus.ti.com/lit/an/slyt084/slyt084.pdf

Have Fun!
Rich
 
J

Jasen Betts

Jan 1, 1970
0
I was asking these questions because having constructed a few of these
circuits in parallel arrangements for use at work, some of them have
packed up completely. Presumably one LED blew and caused the others to
blow.

those flashing leds detailed above are designed to operate off 9v DC. as
long as they are connected correclty. Hook them up backwards and they'll
die pretty quickly. if you're operating them off batteires I'd put a diode
(eg 1N4001) in series with the group of flashing leds to protect against
that.
Is there any way I can prevent this from happening again? Adding a
resistor to each LED? If so what size would you recommend?

not for those LEDS.

Bye.
Jasen
 
N

nick

Jan 1, 1970
0
Jasen said:
those flashing leds detailed above are designed to operate off 9v DC. as
long as they are connected correclty. Hook them up backwards and they'll
die pretty quickly. if you're operating them off batteires I'd put a diode
(eg 1N4001) in series with the group of flashing leds to protect against
that.


not for those LEDS.

Bye.
Jasen

Thanks for your helpful advice everyone!

Nick
 
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