Let's say I have an N-channel FET and some IC, connected as shown. When I set ENABLE to VGS and DATA to 0V, will SER see a LOW signal or a floating input? What if I have a BJT instead of a FET?
Thanks in advance
WHY ? (do you ask ?)
That's a strange circuit.
A mosfet switches on or off depending on the GS voltage differential. But you have the source connected to the SER pin, which appears to be a floating input. So the GS voltage is undefined, and the behavior of mosfet is unpredictable.
Normally you would have the drain connected to SER, which also has a pullup resistor. Then DATA and ENABLE would be connected to the gate and source. It doesn't matter which, but for the mosfet to conduct and drive SER low, the gate has to be high and the source has to be low. Any other state leaves the mosfet off, and the pullup resistor keeps SER high.
You can't really drive SER high through an N-channel mosfet unless you can drive the gate at least a couple volts above the high you're trying to transmit, which is usually not practical.
It would be the same with a bipolar transistor.
So the GS voltage is undefined
Which of course means the circuit is wrong because it is missing the pullup resistor from SER to Vcc.
And FYI,
resistors should be shown going towards the BOTTOM of the page, where GND is assumed to be,
NOT to towards the top or the sides.
WHY ? (do you ask ?)
Please describe what you actually want to do, and forum members can suggest useful approaches.
Is this a signal MOSFET without a body diode? If it has a body diode then the drain cannot be more than a
diode drop more negative than the source. The circuit is clearly back-to-front anyway as the control electrodes
are gate+source, and the controlled one is the drain.
What are you trying to do? Perhaps an AND gate is what you are looking for?
MarkT:
What are you trying to do? Perhaps an AND gate is what you are looking for?
Or may be just a bipolar transistor for OD circuit
Let's say I have an N-channel FET and some IC, connected as shown. When I set ENABLE to VGS and DATA to 0V, will SER see a LOW signal or a floating input? What if I have a BJT instead of a FET?
When I set ENABLE to VGS
Vgs is always UNKNOWN because SER (SOURCE) is UNKNOWN.
In fact Vcc is UNKNOWN.
AND the box with the SER input is UNKNOWN
MarkT:
Is this a signal MOSFET without a body diode?
IIRC you cannot have a MOSFET without a body diode. IIRC a MOSFET is a 4 terminal device but nearly all connect Source to Body (substrate). This also forms the body diode.
IIRC
What does this mean ?
If I Remember Correctly, 
SMISHK!
(Silly Me I Should Have Known !)