23 Oct
2011
23 Oct
'11
5:39 p.m.
Why are the LED drivers so difficult to make, is it
because of the 'high' (a few mA) current ?
Most of the handheld devices of the 70's used multiplexed displays (well, still true
today) and while the average LED current might be a few mA per segment, the peak current
in the drivers could be ten times higher.
Some of the intended-to-be-driven-by-PMOS-driver-chips of the 70's are still around
today and put to other good uses. e.g. ULN2002.
31 Oct
31 Oct
1:19 a.m.
2011/10/24 Shoppa, Tim <tshoppa at wmata.com>
Ahh yes I see.
So if you multiplex 8 leds you need 8 times the peak current to keep the
same luminance ?
Regards
Benjamin
--
Med venlig hilsen / Best regards
Benjamin S?lberg
Why are the
LED drivers so difficult to make, is it because of the
'high' (a few mA)
current ?
Most of the handheld devices of the 70's used multiplexed displays (well,
still true today) and while the average LED current might be a few mA per
segment, the peak current in the drivers could be ten times higher.
Some of the intended-to-be-driven-by-PMOS-driver-chips of the 70's are
still around today and put to other good uses. e.g. ULN2002.
1:29 a.m.
Benjamin S?lberg wrote:
So if you multiplex 8 leds you need 8 times the peak
current to keep the
same luminance ?
8:1 multiplex requires 8 times the peak current to get the same average
power. Years ago I saw some claims that with multiplexing you can use
lower average power for the same perceptual brightness, due to retinal
persistence. However, I've seen other people claim that this is not
true. It would be entertaining to set up a double-blind test and find out.
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benjamin.soelberg＠gmail.com -
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tshoppa＠wmata.com