Ok I’ve been comparing my options as I study Diodes, BJTs, JFETs and MOSFETs again.
Here is an comparison of what I have:
I believe that if I understand the parameters of these devices it will help me understand more clearly the differences of how they work. I just tried reviewing the set up for a 12VDC/195mA solenoid valve I would be powering from a 12V lead acid battery. Its based on an instructable I found which used a BJT (TIP120) with a 1N4004 diode. (http://www.instructables.com/id/Controlling-solenoids-with-arduino/).
Start with the simplest component:
The diode’s most important parameter is the Peak Rep Reverse Voltage from what I gather. The instructable calls for a 4004 but states a 4001 will do. I have a 4007. The values for each are:
4001 - 50V
4004 - 400V
4007 - 1000V
4148 - 100V - I also happen to have a 4148 so I guess I could use this one instead.
What other parameters should I look out for with Diodes besides the VRRM?
Moving on to Switching:
I guess I have seen many tutorials with Arduino about running solenoids with BJTs like the TIP120 because those solenoids used require very little current. If my solenoid draws 194mA at 12VDC, why would the TIP120 not work, or would it? Im looking at the IC which is collector current and its stated as 5A. Am I interpreting that correctly?
Turning over to the MOSFETs, I understand that IRF510 and IRF540 are not LL and so they dont have an RDSon for 4.5V. I also know that mosfets or transistors are meant to be used ON or OFF, but not gradually as I once thought I could get away with milking the IRF510 for the few mA it might produce at 5V at the Base.
It turns out I dont have an IRF510 anyway, what I do have is an IRLB-8721 which is great because it IS a LL mosfet. So Ill start with that.
I just have one doubt about mosfets and datasheets. I was looking at another arduino tutorial that uses a ZVN2110A, which is also not a logic level mosfet. I was thinking, since its Vthreshold is 0.8V-2.4V, I could get a bit of mA out of it. So even though RDSon was 10V = 2A, I figured I might get about 1A at 5V. Then I looked at the curves and saw this:
and thus I realized I didnt really understand these curves. Why does the curve show a reading of about 6.5A at 10V instead of the 2A of RDSon? I just noticed there are two V values, the one on the x-axis and the iso-volt curves. How should I read that graph?