I have some triacs and I'm feeding them DC, 50 ma on the gate but they don't fire the whole sine wave into a resistive load, like the triac which failed after some 30+ years. I thought quadrant I and quadrant III were the requirement, or I have a batch of bad triacs. Can someone lease explain the quadrant specification for triacs?
Triac quadrant definitions please
- Thread starter #12
- Start date
"Traditional" triacs require more gate current to fire if the gate voltage is not the same polarity as the MT2 voltage. Some triacs are optimized to make the triggering current about the same in all four combinations of the gate and MT2 polarities. These combinations are the "quadrants"on the 2-axis graph of gate voltage and MT2 voltage.
Because you are driving the gate from DC, you are operating in one quadrant where the gate is the opposite polarity of the MT2 voltage. Quadrants I and III are with the same polarities.
From page 2 of the attached application note (Make note of the last sentance.):
Triacs can be gated on in one of four basic gating modes as
shown in Figure AN1002.3. The most common quadrants
for gating on Triacs are Quadrants I and III, where the gate
supply is synchronized with the main terminal supply (gate
positive -- MT2 positive, gate negative -- MT2 negative).
Optimum Triac gate sensitivity is achieved when operating
in Quadrants I and III due to the inherent Thyristor chip
construction. If Quadrants I and III cannot be used, the
next best operating modes are Quadrants II and III where
the gate supply has a negative polarity with an AC main
terminal supply. Typically, Quadrant II is approximately
equal in gate sensitivity to Quadrant I; however, latching
current sensitivity in Quadrant II is lowest. Therefore, it is
difficult for Triacs to latch on in Quadrant II when the main
terminal current supply is very low in value.
Special consideration should be given to gating circuit
design when Quadrants I and IV are used in actual
application, because Quadrant IV has the lowest gate
sensitivity of all four operating quadrants.
Because you are driving the gate from DC, you are operating in one quadrant where the gate is the opposite polarity of the MT2 voltage. Quadrants I and III are with the same polarities.
From page 2 of the attached application note (Make note of the last sentance.):
Triacs can be gated on in one of four basic gating modes as
shown in Figure AN1002.3. The most common quadrants
for gating on Triacs are Quadrants I and III, where the gate
supply is synchronized with the main terminal supply (gate
positive -- MT2 positive, gate negative -- MT2 negative).
Optimum Triac gate sensitivity is achieved when operating
in Quadrants I and III due to the inherent Thyristor chip
construction. If Quadrants I and III cannot be used, the
next best operating modes are Quadrants II and III where
the gate supply has a negative polarity with an AC main
terminal supply. Typically, Quadrant II is approximately
equal in gate sensitivity to Quadrant I; however, latching
current sensitivity in Quadrant II is lowest. Therefore, it is
difficult for Triacs to latch on in Quadrant II when the main
terminal current supply is very low in value.
Special consideration should be given to gating circuit
design when Quadrants I and IV are used in actual
application, because Quadrant IV has the lowest gate
sensitivity of all four operating quadrants.
Yebbut. I don't usually do AC drive to AC bigger like a dimmer. I do analog sensing and logic, so I end up with a DC drive available to power whatever the load is.
The only surprise is how many years I got away with not knowing which quadrant I was using.
I always find it disconcerting to find an error in a design that has worked for some time. I find it even more disconcerting to think what other errors are still lurking undetected.The only surprise is how many years I got away with not knowing which quadrant I was using.
