Hi, I need help making a high side switch out of mosfet. The circuit should be activated by +3.3V and be off at 0V, It should deliver +12v up to 5A on an output.
Third circuit on this page.
Leo..
That circuit is for 5V logic, how do I change it to 3.3V both for high side and low side. I am an 82yo tube guy, I have tried several times to learn how to read a datasheet so I can do this myself but I simply do not get it.
Mostly I need logic level MOSFETs, so 12V roughly and 1A, but might need some motor controls so 60V at 5A.
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These are some of the logic level MOSFETs I use in projects, all you need to do is pick the footprint style you can deal with.
Their data sheets are summarized in the PDF. -
Some are discontinued but they will still be available till you are 102
- As already mentioned above.
It is important you keep the gate to source voltage less than the maximum in the data sheet.
Do any of them work with 3.3V?
If you use @LarryD 's circuit, replacing Q1 with an optocoupler, you'll be able to control with 3.3V.
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When you use the a BJT transistor as in the schematic above (Post #4), you don't need to worry about the controller 3.3V.
Controller output as "base current" turns on the BJT transistor not voltage. -
That being said, here is what you look at in the data sheet to see if a MOSFET can be controlled by a certain voltage, in this case 3.3v.
- As mentioned, we do have to make sure the V(GS) maximum is not exceeded with MOSFETs.
It will work with 3.3volt-logic without any modification.
It will even work with 1.8volt-logic.
Leo..
What circuit are we now talking about?
Third circuit in the link I posted (post#2), which is the circuit that @LarryD posted.
The 2N3904 BJT conducts from ~0.5volt, and produces enough collector current (~10mA) with 0.1mA into the base. 1volt into R1 would already be enough.
Leo..
So where it says 5V Pin it can be instead 3.3V?
Does the load voltage HAVE to be 12V? Can it be lower (3.3V or higher 48V)
I can see 3.3V is in range, but do not see 1.8V.
Is a BJT always needed, I was hoping for a MOSFET that works at 3.3V so I can just swap the 5V MOSFET with the 3.3V MOSFET
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Yes.
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The limit is V(gs) of the mosfet, which could be 20volt.
Use circuit#4 if more than 12volt. Change R1 from 330ohm to 220ohm for 3.3volt-logic. -
As explained, 1volt would already be enough to turn the 2N3904 and mosfet ON.
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Yes, you need a level shifter to swing the gate to 12volt to turn the mosfet OFF.
If you switch a 3.3volt supply high-side with a 3.3volt logic pin or if you switch a 5volt supply high-side with 5volt-logic then you don't need a level shifter. A single mosfet will do. See diagram#1 in the link I gave you and imagine it upside-down with a P-channel FET.
Through-hole 3.3volt logic-level P-channel FETs are as rare as hen's teeth.
Leo..
Sorry, i can't understrand
- You need to tell us what part is confusing.
Looks pretty similar to me 
except I've chosen N-channel mosfet instead of a BJT
M2 is drawn backwards, 12V supply should be to source terminal.
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Yes, you can tell this easily by looking at the internal body diode.
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You need the ESP connected to a BJT not a MOSFET.
why not a mosfet?