how can measure latching current (in scr)?

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  • 1 decade ago
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    Note::Ignore the dots

    ............................................................R2...................-.......+..........

    ....................................------------|-----/\/\/\/\/\---------------( A )----|......

    ....................................|..............|...............................................|......

    ....................................|..............|...............................................|......

    ....................................|..............|...............................................|......

    .................................._|_............|.+............................................|......

    ..................................\ /.........(Va)...........................................|......

    ...................................\/..............|.-...........................................(S2).

    .....R1.......+ Ig -........./|...............|................................................|.....

    |--/\/\/\-------(A)--------/ |...............|................................................|.. |..................................|...............|................................................|.....

    ( S1 )..........................|...............|................................................|.....

    |..................................|...............|................................................|.....

    |---------------------------|------------|---------------------------------------|.....

    Well this is the best ASCII drawing I could create.

    So here is the description -->

    S1 : source for providing gate current [can be varied between0 to 30v]

    S2 : SCR power supply [can be varied between0 to 60v]

    R1 = 2.2K

    R2 = 1K/10W

    (A):: ammeter or DMM

    (V)::voltmeters or DMM

    Rig up the above ckt and apply suitable gate current to switch on the SCR

    It is the min. current that should flow between anode to cathode to keep the SCR conducting when the Gate supply is switced off

    To find the holding current--:

    --> switch on the SCR

    -->switch off the gate supply and make sure the SCR is conducting

    -->start reducing the anode voltage and obseve the anode current.

    -->at a particular value the anode current falls to 0. The reading before which the current falls to 0 is the holding current.

    -----------------------------------------------------------------------------

    To find the holding latching current --:

    It is the min. anode to cathode current that should flow through the SCR during turn on, which will keep conducting the SCR even after the removal of the gate supply.

    --> switch on the SCR

    -->adjust the anode current through SCR to its holding current value and remove gate current

    -->if SCR swithecs off, increase the anode current slightly and repeat the above strep.

    -->once again check if the SDC conducts when the gate supply is turned off. If yes, then the anode current is the latching current

    -->at a particular value the anode current falls to 0. The reading before which the current falls to 0 is the holding current.

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