At 11:56 AM 8/21/02 -0400, you wrote:
>I used a 2N3906 and tried the common emitter approach, however I'm
>still getting a voltage drop across the transisitor looks like .8V.
>
>My coil's resistance is about 65 ohms...  Maybe now the drop is due to
>internal resisitance, or is it still the diode drop?

2N3906s are a bit wimpy, but with the proper value of base resistor,
say 470R, (forced beta ~=10) the voltage drop should be around 120mV at
25'C. With the 2N4403, it would be more like 100mV.

>  Maybe a p-channel
>mosfet would be better?  Thoughts?

With a logic-level P-channel mosfet with low Rds(on), sure. But it will
be much more costly than the jellybean BJT, and 120mV is only a couple
percent of 5V.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
9/11 United we Stand

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