CHAPTER 5 - TRIAC

TRIAC’s Introduction

TRIAC or known as Bidirectional Triode Thyristor, electric current can flow in both directions when triggered (turned on). Triggered by a TRIAC can give positive or negative voltage to the gate electrode. Once triggered, it will continue to send components to lower the current flowing from the flow cell, for example at the end of the half cycle of alternating current. TRIAC operation is very similar to the SCR. The difference is when the SCR is connected to the ac circuit, the output voltage is rectified into direct current, while a TRIAC is designed to deliver on the second mid of the output waveform. Therefore, the output of the TRIAC is alternating current, not direct current. TRIAC created to provide a way for enhanced control of ac power

The TRIAC is a semiconductor component that is composed of four layers of structured PNPN diode with three pn junction. TRIAC has three electrodes, namely: gate, MT1, MT2.

If we want to use in the manufacture of devices or TRIAC electronic control systems, there are several things which need attention in choosing TRIAC as follows.

•             Forward and reverse breakover voltage

•             Maximum current (IT max)

•             The minimum cell current (Ih min)

•             Voltage and gate trigger current required

•             Switching speed

•             The maximum voltage dV / dt

•             TRIAC blocking voltage (VDRM)

Symbol and Shape of TRIAC

TRIAC will be connected (on) when it was in the quadrant I that small positive currents passing through the terminal gate to MT1, and MTT2 has higher polarity than MT1. When the TRIAC gate circuit is connected and uncontrolled, then the TRIAC still connected as long as the polarity of MT2 remains higher than MT1 and current flows greater than the current cell (holding current / ick) and TRIAC will also connect when the negative current TRIAC passing through the terminal gate to MT1 and MT1 higher polarity of MT2, and the TRIAC will remain connected even if the circuit does not hold the gate polarity control during higher MT1 MT2. In addition to giving triggering through the gate terminals, TRIAC can also be made connected (on) by providing a high voltage that exceeds the breakover voltage of the MT1 and MT2 of the terminal, but this way is not allowed because it can cause the TRIAC will be damaged. At the time of the TRIAC is connected (on) the forward voltage drop between terminals MT1 and MT2 is very small ranging from 0.5 volts to 2 volts.

TRIAC’s Characteristic curves

In the lighting circuit, current changes in incandescent bulbs will change the amount of light emitted by the lamp. Thus, it can be used as a controller TRIAC light overcast condition. At the same motor circuit, the current changes will alter the speed of the motor.