Contents
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.
What is the latching current of a TRIAC?
The latching current (IL) of a TRIAC is the minimum value of the load current (current flowing between electrodes A2 and A1) that keeps the device conducting when the gate signal is removed (see Figure 1).
What’s the difference between a TRIAC and a SCR?
Triac Vs SCR. Triac is a bidirectional device, whereas SCR is a unidirectional device. Triac terminals are MT2, MT1 and gate whilst SCR has anode, cathode and gate terminals. For both positive and negative gate currents, traic conducts but with only direction on gate current turn ON the SCR.
What are the terminals of a TRIAC circuit?
Instead of having positive anode and negative cathode connections however, the triac’s main current carrying connections are normally labelled MT1 and MT2 signifying Main Terminals 1 and 2 (although other letters may be used) as either terminal can be positive or negative.
When to use TRIAC in electric heater circuit?
When a triac is used in an electric-heater driving circuit, a quick-blow fuse with a current rating greater than that of the heater but less than the maximum current rating of the triac provides adequate protection.
How is the gate drive of a TRIAC controlled?
Most of these devices take the form of a six-pin DIL IC, as shown in Figure 1, and house a simulated triac that has its gate drive controlled via an integral photosensitive zero-crossing detector (ZCD), which can be remotely energized via an integral LED.
Where does the trigger voltage for TRIAC come from?
The triac’s triggering voltage is derived from the VR1 – C1 combination via the Diac (The diac is a bidirectional semiconductor device that helps provide a sharp trigger current pulse to fully turn-ON the triac). At the start of each cycle, C1 charges up via the variable resistor, VR1.
Why does a TRIAC not trigger in each switching mode?
However, because the triac requires differing amounts of gate current in each switching mode of operation, for example Ι+ and ΙΙΙ–, a triac is therefore asymmetrical meaning that it may not trigger at the exact same point for each positive and negative half cycle.
How are TRIAC terminals different from SCR terminals?
Triac terminals are MT2, MT1 and gate whilst SCR has anode, cathode and gate terminals. For both positive and negative gate currents, traic conducts but with only direction on gate current turn ON the SCR. Four different modes of operation are possible with triac, whereas with SCR one mode of operation is possible.
How is phase control used in a TRIAC switching circuit?
Triac Phase Control. Another common type of triac switching circuit uses phase control to vary the amount of voltage, and therefore power applied to a load, in this case a motor, for both the positive and negative halves of the input waveform.
What happens when a TRIAC switch is moved to position B?
If the switch is moved to position B gate current flows at every half cycle the same as before and full power is drawn by the lamp as the triac operates in modes Ι+ and ΙΙΙ–. However this time when the switch is connected to position C, the diode will prevent the triggering of the gate when MT2 is negative as the diode is reverse biased.
How does a TRIAC phase triggering circuit work?
This type of AC motor speed control gives a fully variable and linear control because the voltage can be adjusted from zero to the full applied voltage as shown. This basic phase triggering circuit uses the triac in series with the motor across an AC sinusoidal supply.