Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

How to turn of this MOSFET in the circuit?

Status
Not open for further replies.

xvibe

Member level 5
Joined
Jul 11, 2003
Messages
88
Helped
5
Reputation
10
Reaction score
3
Trophy points
1,288
Location
Portugal
Activity points
783
I have a problem with this circuit (see the atached file please).
When J3 is closed and J4 is open the led is on because the mosfet is conducting.
How could avoid this problem.
This circuit represent a backplane with two cards. And what I want is:
- J4 closed and J3 open or closed (doesn't matter) then LED2 is on.
- J4 open and J3 open or closed (doesn't matter) then LED2 is off.

R3 and R6 represents the loading of each card.

The problem is that or the mosfet is not turning off fast enough or ther's somenting wrong with the circuit.

What to do?
 

If it NMOSFET Apllyiing Voltage 1 to Moscfet input to turn off
If it is PMOSFET apply Voltge 0 to turn off PMOSFET
 

NMOS is off by having a ZERO on the input
PMOS is off by having a ONE on the input

thanks,
Salma:D
 

How can I apply a ZERO when J4 is open?
Note that J4 represents that CARD-1 is out of the backplane. Also, J3 represents that CARD-2 is out of the backplane.
So, how do I detect that J4 is open?

Also, keep in mind that the MOSFET is useded to prevent a reverse polarity of the power supply. Replacing that MOSFET with a diode I can solve the problem. But, the problem is that the circuit needs about 20A and that means a big power loss in the diode.

(Note: R3 and R4 are 2 ohm and not 100 ohm)
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top