# mosfets and current flow

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#### ant17

##### Member level 2 hi guys my first question is will when a circuit exists where a -1vdc source is connected to ground will a current flow to ground as i would of thought of -1 v being potential lower than ground ground and if so why?
second question is if you us use to mosfets with there sources connected to getther to is it possible to make a bidirectional switch which allow current to flow in either diretion but the when the mosfets are turned off no current flows in either direction in both

#### dick_freebird

##### Advanced Member level 5 Your first question is malformed. As to your second, yes;
this is exactly how CMOS-SOI RF switches are made.
There are of course constraints to the application. You
could also make a DC switch this way if you employed
a means of applying a gate charge across an isolation
barrier and stored it across G-{S,B}.

#### ant17

##### Member level 2 sorry if i led you up garden path my fist question is will a -1 volt supply supply a current through a load to ground. and if so why? i don't understand negative voltages

and the second question

what would be the easiest way to implement it

#### crutschow

##### Advanced Member level 5 sorry if i led you up garden path my fist question is will a -1 volt supply supply a current through a load to ground. and if so why? i don't understand negative voltages

and the second question

what would be the easiest way to implement it
Voltage polarity is always relative to some point. Thus voltages are referenced to some common (ground) point as either positive or negative (with respect to ground).
The polarity determines only the direction of current flow, the amount of current is determined by the voltage.
Thus +1V across a given resistor generates as much current as -1V. It's only the current direction that changes.

Another example is a battery. One terminal is labeled positive and one terminal is labeled negative, but that is only with respect to the other terminal.
If you connect the negative terminal to ground then you have a positive voltage from the positive terminal to ground.
If you connect the positive terminal to ground then you have a negative voltage from the negative terminal to ground.
That's how a plus and minus supply can be made.

One example of a low current MOSFET switch is a CMOS CD4066 IC.
For a higher current switch you can connect two MOSFETs together in series, source-to-source.
That will block the voltage in both directions when the gate-source voltage is 0V and conduct when the gate-source voltage is high (10V for a typical MOSFET).

#### ant17

##### Member level 2 ok thanks for that info

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