Could someone please offer their opinion on whether my circuit would work well for turning on an output via a CPLD. The output voltage at PIN0 will be 3.3V. I want logic 1 to turn on my Q1.
Regards, oldmanraskers.
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Could someone please offer their opinion on whether my circuit would work well for turning on an output via a CPLD. The output voltage at PIN0 will be 3.3V. I want logic 1 to turn on my Q1.
Regards, oldmanraskers.
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I have looked at my circuit again and come up with this one. The FET is not the exact one that I'm going to use but I think it would do the job regardless. I considered replacing R4 with a Zener but I'm not sure that is really warranted - what do you think? I'm still sticking with MOSFETs just because I obviously don't know enough about them and want to investigate them further. I do have a question regarding R3 though - I have noticed that the larger R3 is made the slower the gate takes to reach the correct voltage - I assume this is capacitance related to the gate, but I don't understand how to decide what values of R3 would cause me problems - any pointers?
Let me know what you think and thanks for your input thus far.
Regards, oldmanraskers.
This is a fairly bad circuit - you would do much better with an N channel MOSFET (cheaper for same spec) and ground referred drive means it's much less likely to do odd things when you switch. The problem is that you won't easily find a 40V or more rated MOSFET with guaranteed on resistance at 3V gate drive. So I'm with John B on this - you want to drive a solenoid so use a solenoid driver !
It's cheap, needs no additional parts, you get 7 drivers for the price of one, it can drive 300mA with 3V from your CPLD, it comes in a nice DIL package which can go in a socket or not ....... what's not to like !
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MK
