SCR NOT trigger

Discussion in 'General Electronics Chat' started by mostafa_gordy, Apr 9, 2012.

  1. mostafa_gordy

    Thread Starter Member

    Feb 28, 2012
    57
    0
    can i replace SCR with mosfet (IRF840) ?
    How do protect mosfet for back emf ?
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,534
    This is very much on topic for All About Circuits, so I moved it to an appropriate forum.
     
  3. jimkeith

    Active Member

    Oct 26, 2011
    539
    99
    You can replace an SCR with a MOSFET only if you have rectangular triggering--unfortunately, rectangular triggering is not common--it is generally single pulse or pulse train.

    On the schematic provided, it appears that the gate pulse will be too short--to use the MOSFET, you must first determine the ring frequency of the resonant circuit and make sure that the 555 outputs a long enough pulse to run for >½cycle--it also appears that the 555 is wired wrong for astable operation--top of lower 270Ω resistor should connect to pin 7, rather than +12V.

    A series rectifier protects against reverse voltage--this is a common arrangement--for best performance, use fast recovery rectifiers

    My suggestion: Use the SCR--they will work well for the application and do not have the complications introduced with the MOSFET..
     
  4. mostafa_gordy

    Thread Starter Member

    Feb 28, 2012
    57
    0
    hi . firstly, sorry for poor english .
    my bridge diode is blow up(perhaps high current flowing in diode) :confused:and scr is latch up and do not turn off . :mad:
    circuit need resistor ?whats resistor is helpful ? whats location of resistor?
    replace switching section of circuit is need?
    totem-poll ? or push-pull?
     
    Last edited: Apr 10, 2012
  5. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,534
    Ignition coil?

    What is this circuit, as in what does it do?

    Have you read our Terms of Service?
     
  6. mostafa_gordy

    Thread Starter Member

    Feb 28, 2012
    57
    0
    yes! but this circuit for other use(study HV)
     
Loading...