Other than controlling through switch the BT136 can also be controlled through a microcontroller or a microprocessor. Note: Commutation is not required in AC switching circuits because the TRIAC will not latch in on state since the AC voltage reaches zero for every half cycle. To put it simple the TRIAC will remain turned on only till the load current is greater than the holding current of the TRIAC. This commutation is normally done by reducing the load current (forced commutation) less than the holding current. We need special type of circuit called commutation circuit to turn of the SCR again. Since the TRIAC and SCR share most of the same characteristics, just like SCR the TRIAC will also not turn off when the gate voltage is removed. For this to happen, the gate pin of the TRIAC should receive a voltage greater than the threshold gate voltage and should also get a current that is greater than gate trigger current. ![]() In this circuit the TRIAC can be turned using the switch, when the switch is pressed the TRIAC closes the connection for the AC bulb though the AC mains. A simple TRIAC switching circuit is shown below. You can read this article if you want to know more about the switching modes. So this allows the TIRAC to be operated in four different modes. There are many different ways to use a TRIAC, since the device is bi-directional the TRIAC gate can be trigger with either positive voltage or negative voltage. There is chance of backward current when the TRIAC is switching inductive loads, so an alternate discharge path has to be provided for the load to drain the inrush current. In switching circuits the TRIAC is easily subjected to harmonics and EMI interference hence should be isolated from other digital electronics. When controlling the output AC voltage for dimmer or speed control applications a Zero crossing method is always recommended to be used. This problem can be solved by providing a resistance in series for the capacitance to discharge. Due to this the TRIAC will not turn on even if the gate voltage is applied. This occurs due to the capacitance that gets accumulated between the two terminals of the MT1 and MT2 of the TRIAC. Similarly there is another effect called backlash effect. ![]() It can be avoided by using a snubber circuit. This occurs when the TRIAC is switching frequently and a sudden high voltage occurs at either main terminal of the TRIAC and damages the TRIAC itself. Since TRIACS deal with AC voltages, the circuit involving them has to be designed properly to aboid problem some tips are shared belowĪll TRIAC circuits suffer from an effect called Rate Effect. This sensitive gate "series E" triac is intended to be interfaced directly to microcontrollers, logic integrated circuits and other low power gate trigger circuits. Planar passivated sensitive gate four quadrant triac in a SOT78 plastic package intended for use in general purpose bidirectional switching and phase control applications. So if you looking to switch of control (dim, speed control) an AC load which consumes less than 6A with a digital device like microcontroller or microprocessor then BT136 might be the right for you. Since TRIACs are bi-directional switching devices they are commonly used for switching AC applications. The gate threshold voltage of the BT136 is also very less so can be driven by digital circuits. The BT136 is TRIAC with 4A maximum terminal current.
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