• atz88


    MemberJun 30, 2008

    555 Output to MosFET Help

    My circuit is set up perfect so i get the pulse from pin 3 on the 555, im running that to a gate of a mosfet but am having a constantly ON scenario on the Drain an Source of the mosfet with no pulse..

    Could this be because the low pulse on the 555 is still enough voltage to keep the gate open on the mosfet??

    I was tihnking about adding a diode an resistor to +Vs so that i only get the high pulse to the gate of my mosfet?

    Im new to transistors an that a like so if some one could guide me on the requirements that my mosfet needs

    I have a +12 Vs an this is wot is on the output of the 555.
    I need the mosfet operating from 50-500hz .

    As i said before it will be hooked up to pulse a transformer so is there anything else that i need to consider that i don't know about??

    The Amps running through the transformer won't exceed 10amp but how can i decrease the amp flow if it is too high? Resistor in series?

    Thanks in Advance,
    Any Help is really appreciated
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  • umashankar.s

    MemberJul 1, 2008

    generally mosfet is voltage controlled device
    if the Vgs > Vt of mosfet then it ll switch on even though Vds is 0
    this is because a small current flow

    what is the V across D-S? if theres no voltage , then no current or else surely a current ll flow

    u can chk this web page, you will get a clear info
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