need help on Mosfet design suggestions

I think you should go for N-MOSFET....

OK..This is the circuit i am going to use it...kindly check this and suggest me if anything wrong...

https://obrazki.elektroda.pl/58_1302173771.jpg

what is coil current of relay...?
because in your configuration I = V/R => 110/1000 => 110 mA. your current will be less than this value just make sure it is sufficient to energize the relay coil..
or connect the relay coil in series with mosfet as suggested before...

My requirement is 3A load...so i should use only 36R resistor only is it???

Hi venky ,
I think for driving 3A load compare to resistance value,the resistance watt is very important.

OK vetriselvan,
Can u please tell me the resistance value and wattage of resistance????

look for what we are discussing is Relay Switching using Mosfet so the load for Mosfet is Relay (Relay Coil).
the relay coil current shouldn't be 3A it should be the current of the load connected to relays NC,NO and COM terminals...
just check your relay's Coil resistance and nominal voltage and calculate the required current....

hussain_kiet said:

look for what we are discussing is Relay Switching using Mosfet so the load for Mosfet is Relay (Relay Coil).
the relay coil current shouldn't be 3A it should be the current of the load connected to relays NC,NO and COM terminals...
just check your relay's Coil resistance and nominal voltage and calculate the required current....

Click to expand...

I agree with your point....
Actually my requirement is
Each output card drives 16 outputs through solidstate
FET switches. Each switch can drive typically 3 Amps from 110Vdc supply
for driving external relays. Again each of the switches is also provided with short circuit protection

Thanks.....

your requirement is changing every time...
you should post a schematic or block diagram so that we can finally understand your application....

So here we are after 49 posts and we are still in point 0.
Now you tell us that you want solidstate FET switches (not relay as you said before) and in addition short circuit protection...

Alex

alexan_e said:

So here we are after 49 posts and we are still in point 0.
Now you tell us that you want solidstate FET switches (not relay as you said before) and in addition short circuit protection...

Alex

Click to expand...

Hi all,
Really sorry to all...From the previous posts i did not come to the conclusion but i came to the know about P-channel Mosfet and N-channel Mosfet...So for me the previous posts are useful only...I thank everybody...

And here i have attached the document which contains the functional description of the card...
Kindly read it...

hi all,
This is the information i have attached...

Introduction:

Each output card drives 16 outputs through solid-state FET switches. Each switch can drive typically 3 Amps from 110Vdc supply for driving external relays. Again each of the switches is also provided with short circuit protection so that in case of accidental overload or external short-circuit the switch is tripped to protect the switches.


Functional Description of the Output card:

The system has a provision for 80 digital outputs. All outputs are optically isolated. The system is a two out of two system i.e. two processor will work simultaneously and in case of failure of one the other will take the whole responsibility of the system.

Output data from the two-processor cards are first latched on individual buffers. This is crossed checked by the individual processor through feedback ports. The data is then passed through an OR gate to combine the activation signals from the individual processor. A second stage of feedback is provided from this stage. This ORed output is used to drive opto-isolators, which in turn switch ON the MOSFET for driving the external relay.

The driver circuit is short circuit current protected. The current protection is achieved by considering the resistance drop due to over current flowing in the input side, as a result a thyristor will be ON, which pulls the gate to the high voltage towards source; hence put the FET into cut-off. A Zener diode is used between source and gate of the FET, to protect gate to source break down, due to some fault in the circuit.