MOSFET as Load switch

[suryakant]

mosfet load switch

Hi all,
I am using MOSFET to switch on/off supply to one section of my circuit. Supply voltage is 3.3V

The circuit is attached here.

When PS_Control is HIGH, I get 3.3V.
But, when PS_Control is low, still I am getting approximately 1V at the output. But i want the voltage to be zero. Whats the reason for this? Do I need to modify the circuit?

Thanks.

 

[IanP]

load switch

When the MOSFET is OFF Test-Point VL_3.3V is floating .. and you have a tiny leakage current ..
Try to add a "dummy" load of, say, 100kΩ that will pull the voltage down to 0V ..

Rgds,
IanP

 

[suryakant]

mosfet as a switch

Hi IanP,

Actually load is 2 op-amps LMV324. I also tried to put dummy load, but no help!!!
Its still at about 1V.

But if I replace BJT by N channel MOSFET, it works fine......

I am just wondering what would be the reason.

 

[FvM]

mosfet switch

Either the real circuit is different from your schematics, PS_CONTROL is above 0.6V in low state or the transistor is defective.

 

[antonic54]

Re: mosfet as a switch

Hi IanP,

Actually load is 2 op-amps LMV324. I also tried to put dummy load, but no help!!!
Its still at about 1V.

But if I replace BJT by N channel MOSFET, it works fine......

I am just wondering what would be the reason.

Hi Suryakant,

can you put the schematic with thr BJT replaced with n-channel Mosfet?
Thank you a lot, Antonio

 

[ganesamoorthy]

Unlike bipolar transistors, power MOSFETs have a considerable
gate capacitance that must be charged beyond the threshold
voltage, VGS(TH)
, to achieve turn-on. The gate driver must provide
a high enough output current to charge the equivalent gate capacitance, CEI
, within the time required by the system design.

https://ww1.microchip.com/downloads/en/AppNotes/00786a.pdf