Hi,
'Quadrant' (3 or 4) term sounds new to me in Triac, I didn't read before. May I know about it in simple?
Hy Willen,
Triac quadrants are dead simple:
(1)
Equivalent Circuit
(1.1) The name triac is derived from 'triode for AC' which is a complete misnomer.
(1.2) The image on the left shows that the equivalent circuit of a thyristor comprises two complementary transistors, and the image on the right shows that the equivalent circuit of a triac is two thyristors connected in reverse parallel. You can actually make a thyristor from an NPN transistor, a PNP transistor, and a couple of resistors. It thus follows that you could make a triac from two NPN transistors, two PNP transistors and a few resistors.
(2)
Trigger
(2.2) A triac switches AC current and is turned on by a signal between the gate and anode 1, when there is a voltage, either positive or negative, on anode 2.
(2.3) Triacs cannot be turned off by a signal on the gate (gate turn off [GTO] devices can be turned off by the gate signal).
(2.4) Once conducting, triacs can only be turned off is by reducing the anode current to below the triac holding current.
(2.5) The gate signal is typically 1.2V at a current of 500uA, 1mA_5mA_10mA, 20mA, 30mA, 50mA, 100mA or 150mA, depending on the triac. Normally the higher current triacs require higher gate current to trigger.
(3)
Quadrants
(3.1) There are four relationships that can occur with the gate signal:
(3.2) Anode2 positive, gate positive (quadrant #1)
(3.3) Anode2 positive, gate negative (quadrant #2)
(3.4) Anode2 negative gate negative (quadrant #3)
(3.5) Anode2 negative gate positive (quadrant #4)
(for some bizarre reason Anode 1 is also known as Main Terminal 1 (MT1) and Anode 2 is known as MT2)
(3.6) Early triacs generally triggered in all four quadrants, but some of the new 'High Commutation' (HiCom) triacs only trigger in quadrants one, two, and three (some HiCom triacs will trigger in quadrant four, but only at a higher current, typically double).
(4)
Commutation
(4.1) With certain loads, especially inductive, normal triacs may not trigger or falsely trigger, so you need to fit snubber circuits, but theses can get quite complex and expensive, especially where high voltages and currents are involved.
(4.2) Because of this, a new breed of triacs were introduced. These are known as HiCom types.
https://www.st.com/content/ccc/reso...df/jcr:content/translations/en.CD00002263.pdf
(4.3) HiCom triacs only trigger in three quadrants and they generally need more trigger current (but not more voltage). Typical HiCom triac trigger current would be 50mA or 100mA for a 20 Amp to 50 Amp TRIAC.
(5)
Logic Level
(5.1) There is another breed of triacs know as 'Logic Level'. Theses have trigger currents of 500uA to 10mA and can be triggered by logic circuits, including MCUs.
(5.2) Logic Level TRIACs generally trigger in four quadrants and are not HiCom types. They also tend to be limited to lower currents, around 10 Amps maximum.
(5.3) But recently, another breed of Logic Level triacs have been introduced which are HiCom and only trigger in three quadrants.
https://www.st.com/content/ccc/reso...df/jcr:content/translations/en.DM00104272.pdf
(6)
Maximum Voltage and Current Change Rate
(6.1) Two things that often gets missed when using triacs (and thyristors) are the maximum rate of voltage change (dV/dt) and maximum rate of current change (dI/dt). If you exceed the former the triac can turn on without a gate signal, and if you exceed the latter the triac can be damaged.
spec
LINKS
(1) **broken link removed**