Editing TRIAC (section)

==Snubber circuits==
When used to control reactive ([[inductor|inductive]] or capacitive) loads, care must be taken to ensure that the TRIAC turns off correctly at the end of each half-cycle of the AC in the main circuit. TRIACs can be sensitive to fast voltage changes (dv/dt) between MT1 and MT2, so a phase shift between current and voltage caused by reactive loads can lead to a voltage step that can turn the thyristor on erroneously.<ref name="PowerElec"/> An electric motor is typically an inductive load and off-line power supplies—as used in most TVs and computers—are capacitive.

Unwanted turn-ons can be avoided by using a [[Snubber|snubber circuit]] (usually of the resistor/capacitor or resistor/capacitor/inductor type) between MT1 and MT2. Snubber circuits are also used to prevent premature triggering, caused for example by voltage spikes in the mains supply.

Because turn-ons are caused by internal capacitive currents flowing into the gate as a consequence of a high d''v''/d''t'', (i.e., rapid voltage change) a gate resistor or capacitor (or both in parallel) may be connected between the gate and MT1 to provide a low-impedance path to MT1 and further prevent false triggering. This, however, increases the required trigger current or adds latency due to capacitor charging. On the other hand, a resistor between the gate and MT1 helps draw leakage currents out of the device, thus improving the performance of the TRIAC at high temperature, where the maximum allowed d''v''/d''t'' is lower. Values of resistors less than 1kΩ and capacitors of 100nF are generally suitable for this purpose, although the fine-tuning should be done on the particular device model.<ref name="AN3008"/>

For higher-powered, more-demanding loads, two [[Silicon-controlled rectifier|SCRs]] in inverse parallel may be used instead of one TRIAC. Because each SCR will have an entire half-cycle of reverse polarity voltage applied to it, turn-off of the SCRs is assured, no matter what the character of the load. However, due to the separate gates, proper triggering of the SCRs is more complex than triggering a TRIAC.

TRIACs may also fail to turn on reliably with reactive loads if the current [[Phase (waves)#Phase shift|phase shift]] causes the main circuit current to be below the [[Silicon controlled rectifier#Modes of operation|holding current]] at trigger time. To overcome the problem DC or a [[pulse wave|pulse train]] may be used to repeatedly trigger the TRIAC until it turns on.