Velleman SCR100 - Manual (Page 8)

Atlas SCR User Guide January 2008 – Rev 3
Page 8
Notes on SCRs and Triacs
Silicon Controlled Rectifiers
SCR Turn-On
SCRs (Thyristors) act as a controlled diode. They block reverse current at all
times, and they conduct in the forward direction only when triggered by a pulse
of current to the control (gate) terminal. Once triggered, the SCR will continue
to conduct current in the forward direction until the device is turned off.
SCR Turn-Off
In order to turn off a triggered SCR, it is necessary to reduce the main terminal
current below the holding current for typically 5-200
µS. Shorter periods may
leave insufficient time for free charge carriers to recombine, and thus when
main current is reapplied, the device may remain triggered.