Velleman DCA75 - Manual (Page 27)

Atlas DCA Pro User Guide December 2012 – Rev 1
Page 27
Thyristor (SCR)
Red-G Green-K Blue-A
Triac
Red-MT1 Green-G
Blue-MT2
Thyristors (SCRs) and Triacs
Sensitive low power thyristors (Silicon Controlled
Rectifiers - SCRs) and triacs that require gate
currents and holding currents of less than 10mA
can be identified and analysed with the DCA Pro.
Thyristor terminals are the anode (A), cathode (K) and the gate (G).
This example shows that a thyristor has
been detected:
Triac terminals are MT1, MT2 (MT
standing for main terminal) and gate.
MT1 is the terminal with which gate
current is referenced.
1. The unit determines that the device under test is a triac by checking
the gate trigger quadrants that the device will reliably operate in.
Thyristors operate in only one quadrant (positive gate current, positive
anode current). Triacs can typically operate in three or four quadrants,
hence their use in AC control applications.
2. The gate trigger currents used by the DCA Pro are limited to less
than 10mA. Some thyristors and triacs will not operate at low currents
and these types cannot be analysed with this instrument. Note also that
if only one trigger quadrant of a triac is detected then the unit will
conclude that it has found a thyristor. Please see the technical
specifications for more details. The Atlas SCR (model SCR100)
instrument is designed for analysing triacs and thyristors that require
currents up to 100mA to operate.