Which MOSFET transistor or other component would have 6V min switching voltage?
Which MOSFET transistor or other component would have 6V min switching voltage?  



If by "6V min switching voltage" you mean "which transistor will have a voltage drop lower than 6 V when driven into saturation (fully on)", practically every transistor ever. Silicon bipolar transistors will have a voltage drop (Vce(sat)) typically somewhere between 100 mV and 2 V. Field effect transistors (e.g. MOSFETs and JFETs) are different, and the voltage drop is very dependent on the current (they act more like resistors).
If you mean "which transistor will be able to block 6 V without breaking", practically every general purpose transistor and power transistor of any type ever.  
If you mean "which transistor will turn on only after the control input reaches 6 V", bipolar transistors don't behave like this at all (they are current driven). Some MOSFETs and IGBTs have a gate threshold voltage (Vgs(th)) in this range, but they won't be completely off at 5.99 V and fully on at 6 V if that is what you want. They will instead gradually start to conduct more and more current (Id) as the gate voltage rises:  


  


  Switch to be "on" when supply voltage is 10V or greater. Below 10 V switch need to be off while input is still connected to supply voltage but les then 10V.


To do this, you need a voltage comparator and a switching element. A comparator will have two inputs ("+" and "-") and one output. The output will be high (at supply voltage) whenever the inverting input ("-") is at a lower voltage than the non-inverting input ("+"), and low (close to ground) whenever the opposite is true.  







simulate this circuit &ndash; Schematic created using CircuitLab

Unfortunately a comparator (CMP1) cannot drive high current loads directly, but you can fix this by using the comparator output to control a switching element which then handles the high current load. A N-channel power MOSFET (M1) would serve this role well. The diode D2 is there to protect the MOSFET from inductive voltage transients when it switches off.

To "know" the input voltage, the comparator needs to have a voltage reference to compare the input voltage with. In this case the referene is 3.6 V, but it can be any voltage lower than the minimum expected input voltage. A zener diode(D1) with a resistor (R1) in series will work just fine here, but voltage reference ICs are a better choice if high precision and/or stability is required.  

The threshold selection is just a single potentiometer. It acts as a voltage divider, dividing the input voltage by a configurable ratio. By adjusting it you can change the minimum input voltage level which will turn the output on. For example if you want the output to switch on at about 10 V, you would turn the potentiometer until the voltage at the non-inverting input ("+") of the comparator is 36% of the input voltage, so that it matches the 3.6 V reference at 10 V.  

One more thing: When the output voltage rises just above 10 V and the load is switched on, the current will suddently increase and the input voltage will fall. This fall in input voltage will then cause the comparator to switch the load off, causing the input voltage to rise, causing the comparator to switch the load back on, and so on. To get rid of this oscillation, positive feedback (hysteresis) is added to the circuit in the form of R3: 


When the input voltage rises above say 10.23 V, the comparator switches on and R3 will lower the threshold for switching off to 9.97 V
When the input voltage then falls below 9.97 V, the threshold for switching on will become 10.23 V.