Re: Transistor questions

John Popelish wrote:
Digitmode@xxxxxxxxx wrote:
Hey thanks for the help, the PNP transistor is sounding like a much
better idea. I run into one snag though, the PNP's I have can only
support a max of 100mA at the collector and my load is six leds at 20mA
each, so I need atleast +120mA. This is where I was heading asking
about using 2 transistors on one output to split the load. I need to
know how to calculate the resistor values need for the transistor.

IC specs: SN74LC148 http://focus.ti.com/lit/ds/symlink/sn74ls148.pdf

There are bigger transistors, like 2N4403.
http://www.fairchildsemi.com/ds/2N%2F2N4403.pdf

But with a 12 volt LED supply, are you willing to string 2
or 3 LEDs in series and run them on a single 20 milliamp
current? That would make use of the supply a lot more
efficiently.



Sorry I forgot to say I was running the leds in parrallel, thier
voltage drop is about 4 to 4.5v so my only other option would be 3 rows
of 2.

.

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