How Much Current Can A BS2p24 Sink??

Archiver

In a message dated 6/18/2004 7:57:19 PM Eastern Daylight Time,
tboonefisher@s... writes:


> I need to use a BS2P24 output to switch
> an LED that is connected to a +12.5V(up to 15V)
> supply via a 1.5Kohm series resistor. The stamp will pull
> the line low to light the LED. I figure the stamp will need
> to sink at least 8.7ma to do this. Is this a problem or do
> I need to add more series resistance or a buffer device?
> TIA,
>

You could saute your BS2P. Use a transistor to turn the LED one or off.

Sid


[noparse][[/noparse]Non-text portions of this message have been removed]

Archiver

I need to use a BS2P24 output to switch
an LED that is connected to a +12.5V(up to 15V)
supply via a 1.5Kohm series resistor. The stamp will pull
the line low to light the LED. I figure the stamp will need
to sink at least 8.7ma to do this. Is this a problem or do
I need to add more series resistance or a buffer device?
TIA,
Tom Fisher
Dallas,TX

Archiver

Tom,

Even though the current might be within limits, the voltage isn't. When the
LED is off, the Stamp pin will "feel" the full supply voltage, and anything
over 5V is a major no-no.

You can use an inexpensive NPN transistor such as a 2N3904, PN2222, or
2N4001. At the current level you are controlling, a 4.7k ohm resistor would
supply plenty of base current to the switching transistor. Connect the
transistor's emitter to ground, the collector to your load, and connect the
4.7k resistor between the Stamp's I/O pin and the transistor's base. The
other side of the load is connected to B+. Anything from 1k to 10k ohm
should work fine for the base resistance if you don't have a 4.7k handy.

The first schematic at

http://www.glitchbuster.com/pwrswtch.htm

sort of shows it. Take a look at how R1 and Q1 are connected. (Eliminate
the pushbutton switch, R2, and Q2). Your LED/series resistor would be
connected between B+ and the "top" (collector) of Q1.

Hope that helps,

-Randy
www.glitchbuster.com




> I need to use a BS2P24 output to switch
> an LED that is connected to a +12.5V(up to 15V)
> supply via a 1.5Kohm series resistor. The stamp will pull
> the line low to light the LED. I figure the stamp will need
> to sink at least 8.7ma to do this. Is this a problem or do
> I need to add more series resistance or a buffer device?
> TIA,
> Tom Fisher
> Dallas,TX