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Sorry it's been so long since I responded to this post, just been busy with other stuff...
Look for parts that have Rds(on) specified at 2.5V. this one will have maximum 0.065 ohm resistance with 2.5V gate voltage. beginners make the mistake of looking at the spec for gate threshold voltage, but that is specified at very low current level. this MOSFET will start to turn on at typically 0.9V, but to drive high current you need more gate voltage. a 3.3V GPIO can drive this MOSFET with drain currents over 4A.
I read the article linked by Gordon about MOSFET's and it's actually pointing to Vgs being the specification I should look for... Why would knowing the resistance levels with 2.5V on the gate tell me how much current can be passed through the transistor? Actually, I'm really starting to get confused now after looking at that transistor datasheet you linked, the graph from figure 3 says there would be much much more current than 4A flowing through the transistor with just 2.5 V for Vgs...
Also, for the general purpose BJT, I'm confused as to how much current needs to be applied to the base for the collector/emitter to reach the peak 40V given the saturation levels I highlighted in the OP...
Thanks :-)
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user52526
@tage
you are on the right track. Vce(sat) indicates what voltage drop to expect across collector-emitter with (in this case) 10mA collector current and 1mA base current.
(http://diodes.com/datasheets/ZXMN2F30FH.pdf)
if you want to control a transistor with a GPIO pin, have a look at n-channel MOSFETs such as ZXMN2F30FH. there are dozens of part names to choose between. Look for parts that have Rds(on) specified at 2.5V. this one will have maximum 0.065 ohm resistance with 2.5V gate voltage. beginners make the mistake of looking at the spec for gate threshold voltage, but that is specified at very low current level. this MOSFET will start to turn on at typically 0.9V, but to drive high current you need more gate voltage. a 3.3V GPIO can drive this MOSFET with drain currents over 4A.