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

Thread Starter

hants91

Joined Jul 20, 2011
1
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.

Thanks
 

bertus

Joined Apr 5, 2008
21,595
Hello,

I have moved your post to the general chat area.

Can you post a schematic of the intended circuit?

Bertus
 

tom66

Joined May 9, 2009
2,595
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.
 

SgtWookie

Joined Jul 17, 2007
22,221
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.
 

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