NO switch with MOSFET/JFET, Vs=3V, no neg V

Thread Starter


Joined Jul 20, 2011
Hi, I am new to the forum and looking for some help. I have a circuit which I want to power up when a switch (operated by mechanically) is in Open state. I do not want to used relay.

State 1: Switch Open - Circuit Power ON
State 2: Switch Closed - Circuit Power Off

I considered P-channel MOSFET IRML5103, when the Gate is grounded State 1 activated. But for State 2, I need neg. supply at Gate which I do not have.

P-N-P transistor can do the job. But it have 0.7 voltage drop which is not acceptable as the unit run by 3V battery and the circuit can run upto 2.2 V.

I appreciate your suggestions.



Joined Apr 5, 2008

I have moved your post to the general chat area.

Can you post a schematic of the intended circuit?



Joined May 9, 2009
You do not necessarily need a negative supply for the PMOS. If the PMOS is on the high side of the load, then pulling the gate low will turn it on; letting it float to the drain voltage will turn it off. Ensure Vgs never exceeds +/-20V though; you might use a zener and series resistor for this.


Joined Jul 17, 2007
You didn't state what your loads' current requirement is.

Here's one way you might do it with a couple of PNP transistors and some resistors:

The resistors were calculated for a 3mA load, and Q2 as having a gain of 70.