S.C.R

S.C.R

1. V.I. characteristics

   • GRAPH
     • FORWARD BREAK OVER VOLTAGE
     • FORWARD LEAKAGE CURRENT
     • HOLDING CURRENT
       • importaint at time of SCR turn off
       • defined as zero gate current
       • if Vak < Vh:scr will turn off
     • LATCHING CURRENT
       • importaint at the time of SCR turn on
       • IL>Ih
       • if Ia at the time of turn on is higher than latching current then nly scr will latch into on state
       • if Ia <IL the scr will not latch:it will remain on as long as ig is supplied.As soon as ig is 0 the scr will turn off
     • Ig1-Ig4
   • forward characteristics
     • forward blocking state
       • high voltage,low current =OFF STATE
       • forward leakage current
         • minority carriers
     • ON state
       • Vscr is low
         • avg currents as large as 2000amp,with on state v drop of few volts
     • transition state
       • Vak<Vbo
       • Vak>Vbo
         • Ia increases sharply,Vscr reduces sharply
   • reverse characteristics

2. construction

   • 4 layer PNPN
     • 3 terminals bought
       • GATE=CONTROL
   • 3 JUNCTIONS
     • scr -forward biased

3. SYMBOL

   • UNIDIRECTIONAL DEVCICE