Contents
Why triac is bidirectional?
The triac is an important member of the thyristor family of devices. It is a bidirectional device that can pass the current in both forward and reverse biased conditions and hence it is an AC control device. The triac is equivalent to two back to back SCRs connected with one gate terminal as shown in figure.
What is the advantage of TRIAC over SCR?
Advantages of Triac It requires only a single heat sink of slightly larger size, whereas for SCR, two heat sinks should be required of smaller size. It requires single fuse for protection. A safe breakdown in either direction is possible but for SCR protection should be given with parallel diode.
What are the advantages and disadvantages of a triac over SCR?
How is a TRIAC gate triggered in an AC circuit?
It can be triggered by either a positive or a negative voltage being applied to its gate electrode. Once triggered, the device continues to conduct until the current through it drops below a certain threshold value, the holding current, such as at the end of a half‐cycle of alternating current (AC) main power.
How is the current flow in a TRIAC circuit?
The TRIAC allows current to flow in either direction with flow changing with the polarity of the gate voltage. The gate voltage can be derived from the AC voltage applied to the TRIAC’s load terminals. If the application requires current flow in only one direction, a diode is connected in series to the gate to convert the AC voltage to DC.
What causes the TRIAC to conduct in both directions?
A small leakage current flows through the device until it is triggered by breakover voltage or gate triggering method. Hence the positive or negative pulse to the gate triggers the triac in both directions. The supply voltage at which the triac starts conducting depends on the gate current.
When does a gate trigger signal need to be used?
The gate trigger current is needed to re‐bias the junctions within the triac every half cycle when the load current passes through zero. Secondarily, if the holding current is too low and leakage current or noise is experienced in the triac or line, respectively, there is unintended turn‐on of the triac in the absence of gate trigger signal.