Hello guys.
I want to make sure if this configuration I have created (based on topics read on this forum) is going to work in long term.
I already connected it and it seems to be doing ok but I need high reliability for this project since I'm not at home very often.
Schematics in the attachment.
Did I chose resistor values correctly?
Is R3 resistor even necessary in here?
Will 2N7000 be able to last for long if it's going to run with 200mA current, which is it's peak continuous value?
No! Completely obsolete device - 74LS series. Use a 74HC04. In general, do not even replace 74LS devices with same,
R3 is in wrong place and unnecessary. If you did need a pull-down which you do not because the 74HC04 will either switch the FET on or off so a pull-down is meaningless, then you would put the pull-down on the output of the tri-state device which might not be in a defined state during start-up.
And given you are driving a logic-level FET, a 74LS device will not drive it properly in any case. OK, the 2N7000 is sort of a logic level device, but you certainly should not operate it at its maximum rating. 200 mA at 6 Ohms Vds, 1.2 V drop, 240 mW - getting a bit close. Use a better FET.
Thanks for the response.
Alright I'm definitely gonna go with 74HC04 then, what about mosfet? I'm thinking about IRLZ14 which seems to be a bit of an overkill but should work. Please let me know if I'm wrong.
There is one more thing I forgot to mention which is tlc's IREF pin as far as i know it's suppose to limit current on the outputs, since my outputs aren't connected directly to the ground nor through some low resistance elements, does the resistance connected to IREF make any deifference? Guess I'll just connect 2k2 resistor to limit current up to 20mA.
