Re: Multiplexing LEDs - calculating resistor value
"roxlu" <diederickh@xxxxxxxxx> wrote:
My previous post about speeding up multiplexing resulted in a display
with
8x48 LEDs. As I suggested and read, the LEDs are becomming less bright
when more than 2 LEDs are on in a matrx of 8x48 >=.
Here is a small part of the circuit to show the current limiting
resistor of 100R.
http://imagebin.org/5461
It sounds like you are still driving the matrix wrong. With the circuit you
linked only one bit in the row shift register should be on so only one LED
connected to that 100R resistor will be on at a time and that LED gets the
whole 21 mA.
When you start driving the matrix the right way remember all 48 LEDs could
be on and the row drivers will have to source just over 1 Amp which the
transistors you chose may not be capable of.
--
.
Relevant Pages
- Re: Cant get enough current for 1W Luexon LED even without resistor
... resistor but still only about 100ma current. ... want to be thinking in terms of voltage. ... life from any high power LED, is to pulse drive it. ... The level of these that some high power LEDs can ...
(sci.electronics.repair) - Re: Cant get enough current for 1W Luexon LED even without resistor
... Then I tried without the resistor but ... the LED I have to raise the voltage to about 11V and of course I ... LEDs for a long time, and never suffered a problem with a switch-on ... max forward current quoted in specs, is for a short duration pulse. ...
(sci.electronics.repair) - Resistors for LEDs: the real answer
... First of all, while non-electronics types refer to the resistor in this use as a "dropping resistor", that's not really technically accurate: whats actually going on is that you're making a voltage divider network with a resistor in series with the LED. ... By putting a resistor in series with the LED, you're dividing the 24 volts between the resistor and the LED, because the whole idea is to make sure that the LED doesn't get too many volts and blow. ... Turning to my handy-dandy Jameco catalog, it appears that most garden-variety LEDs are rated at about 2 volts, some more, some less: close enough to be no never mind. ...
(rec.models.railroad) - Re: Resistors for LEDs: the real answer
... while non-electronics types refer to the resistor in this ... whats actually going on is that you're making a voltage divider network ... Obviously, if you just put the poor LED across the 24 volts, ... the great majority of LEDs are rated at 20 mA; ...
(rec.models.railroad) - Re: Right resistor for high power LED for sound reader?
... I'm a projectionist in a movie theater. ... >>>The soundtrack runs along one side of the film, ... what kind of resistor would I use to get this LED to work? ... The chips in these LEDs have a nonlinearity, ...
(sci.electronics.basics) |
|
