Connecting LEDs in series-parallel like the ASCII schem below is okay? I don't see any reason why it shouldn't work. If a lot of LEDs, like the 7 below, are paralleled, the total current for each parallel string should be an average, i.e. some LEDs will draw more, some less, so they should average out. So the diff between the two strings should be minimal. But if one parallel string draws a few more milliamps, the V drop will be less for this string, and more for the other string. But this diff should also be minimal.The reason for this configuration is that the PC board is laid out for ICs, and this connection pattern is more convenient, with less trace cutting and jumpering.Typical resistors are 51 ohms, 3.5V across each white LED, about 9.6V for LED current of 30 mA each.View with Courier Font +V | +----+----+---------+--- - - | | | / / / Resistors / / / | | | 7 total _|_ _|_ _|_ /-> /-> /-> --- --- --- LEDs | | | | | | +----+----+---------+--- - - | | +----+----+---------+--- - - | | | / / / Resistors / / / | | | 7 total _|_ _|_ _|_ /-> /-> /-> --- --- --- LEDs | | | | | | +----+----+---------+--- - - | -V-- @@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@###Got a Question about ELECTRONICS? Check HERE First:### email address is whitelisted. *All* email sent to it goes directly to the trash unless you add NOSPAM in the Subject: line with other stuff. alondra101 Don't be ripped off by the big book dealers. Go to the URLthat will give you...

Hi Watson- Not sure if I missed somewhere in your posts butdid you ever run any of your LED projects in the pulsed modesimilar to strobbing as used in 7-segment displays as used incalculators? Efficiency of LED's goes up significantly in thepulsed mode. Early HP calculators such as the HP35 Serieswent another step farther to improve battery life by usinginductors to discharge into the LED's & avoid losses in resistors.Still have my HP67 running. Got it in 1975 while at HP.Part of my time there selling the Opto line.Cheers, John Stewart

---Obviously not ------"Current limiting" resistors don't you mean? I believe the resistorsshown _are_ current sharing resistors.------Totally unnecessary in _this_ application, since a separate currentlimiting resistor is provided for each LED.------So what's your point?-- John Fields

LEDs Series-Parallel OK?

Oct 29, 2003 22 Replies

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Watson A.Name "Watt Sun - the 22 years ago

I appreciate the concerns. I think, from reading the other LED "overclockers" on such blogs as Candlepower Forums, that the 30 mA issue isn't really a problem. The higher current is probably going to shorten the life of the LED, but not dramatically. Like they don't seem to be concerned about running an average of 30 mA, with substantially more current when the batteries are fresh, maybe 40 or 50 mA. The amount of time that the LED is at this higher current isn't a lot, it tapers off quickly as the batteries get 'unfresh'. In the case of the little keychain squeeze lights, they don't even use a resistor, just the battery internal resistance. :-P

@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@ ###Got a Question about ELECTRONICS? Check HERE First:### http://users.pandora.be/educypedia/electronics/databank.htm My email address is whitelisted. *All* email sent to it goes directly to the trash unless you add NOSPAM in the Subject: line with other stuff. alondra101 hotmail.com Don't be ripped off by the big book dealers. Go to the URL that will give you a choice and save you money(up to half). http://www.everybookstore.com You'll be glad you did! Just when you thought you had all this figured out, the gov't changed it: http://physics.nist.gov/cuu/Units/binary.html I speak only for myself, no one else, & they're my opinions @@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@

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DarkMatter 22 years ago

On Thu, 30 Oct 2003 04:30:07 GMT, "Jeff" Gave us:

One is much better off placing an LED in series with a resistor. Make several. Place them on a pair of rails that are fed by a constant voltage source that is regulated.

VIOLA!

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John Fields 22 years ago

Obviously not

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