Fan OK circuit

[dannix]

Here is the amended schematic, Im not sure how it works, but as long as it does i'm not complaining

 

[dannix]

here it is, really:

 

[yngndrw]

Okay now that I can post I thought I'd post one of the latest(ish) revisions of the circuit for anybody interested.

There's few bugs but they are being worked on. ;o

 

[dannix]

Its been sometime but i had to put this all on hold. Anyway I have been working to get this fan monitor and mosfet driver working. Here is what I have now, I prototyped and it worked but was not driving the mosfet properly. So here is what I did to fix that.

Is the way the MOSFET being driven ok? it works in simulation but I dont have the components to prototype at the moment. Please see attached schematic. Any ideas to reduce overall power consumption are welcome!

 

[yngndrw]

I don't use MOSFETs a lot so I could be wrong but it looks alright to be. Just make sure that you use a TTL MOSFET. (Triggered from 5V instead of the normal ~10V.)

 

[dannix]

Hay! That was my concern, im not sure the current output of the AND is sufficient to drive the mosfet, altough in simulation it seems to be. I will soon find out when my supplies arrive...

I just came across the term TTL mosfets, not seen or heard of them before, are they able to switch say 3A?
I also thought of putting a transistor in C - 12v switched E - mosfet gate and B AND output, it then got me thinking, i tried to drive the transistor from the fan signal an ddo away with the AND gate, but it wont work in simulation

 

[dannix]

I have changed a few things to reduce component count. I removed the AND gate and replaced with a transistor as I was worried it would not cope with the current for the mosfet. Attached is my current schematic.

Would appreciate any comments, if I can reduce curent consumption any further that would be good. And of course any reasons why this would not work in real life.

Thank in advance!

 

[yngndrw]

A MOSFET is voltage triggered, therefore it doesn't really require any current to operate.

Another thing is that I think MOSFETs require their input to be pulled both high and low. Using a transistor you can only pull the gate high, therefore it will never switch off. I honestly think you're better off with the AND gate.