MOSFET AS A SWITCH FOR RELAY -- ARE DIODES NEEDED?

[pfaisalbe]

MOSFET AS A SWITCH

Hi

I wish to use MOSFET as a switch using electromechanical relays. I don't have the relay specification at this point. I came to know that , to avoid back emf I need to use freewheeling diode. I have found sample circuits as well. I will use PC parallel port to control the gate.

I am stucked in the design part.

I know that Rds and power dissipation parameters of MOSFET are necessary.Apart from that what are the other parameters i need to know for designing this circuit?

How to choose a Freewheeling diode fora particular inductive load ?

Please help

Thanks in advance

Faisal

 

[karesz]

MOSFET AS A SWITCH

Hi,
Modern MOSFETS hase onchip diodes...
You must check for sufficient Uds & Ids values, select your appropiated package.
If you will select a "Logic Fet" (Ugs threshold at 2V)_it will direct controllable width your general logic...
#1230960
K.