BT136 TRIAC waveform

Question

I am using a TRIAC to switch an AC signal
(a typical example is shown in question Triac Switch Circuit using MOC3021 and BT136).

When a BT136 TRIAC is used to switch a pure sinewave signal, I want to know the output wave form, when

1. +3.3VDC is applied to the GATE (my expectation is: pure sine-wave)

2. +3.3VAC is applied to the GATE (my expectation is: trimmed-sinewave depending on +/-VBO)

I want a pure sine-wave on the output but I don't want to use an external/constant-power-source/battery to drive the gate.

Answer 1

Applying +3.3V to the gate relative to the MT1 will likely destroy the triac and you might well get a pure sine wave (even after the +3.3V is removed). A controlled current of >25mA will work without destroying the triac. A negative current is better because it avoids the insensitive quadrant where gate is + and MT2 is -.

Applying 3.3VAC will also destroy the triac. If you intend to trigger it the current must be limited and it will depend on the frequency and phase of the applied AC current.

If you want to pass current without current drain maybe you can use the N.C. contact of a mechanical relay.

Answer 2

As Spehro says, a suitably current limited drive using a 3.3V DC source will allow a pure sinewave output.

Current limited AC gate drive in phase with the switched AC will result in off periods after each zero crossing while the gate drive voltage rises to a value able to provide adequate drive current.

If you have 3.3 VAC available then you can rectify it and provide a "local" DC voltage to drive the gate with DC. This should meet you requirement.

What is the switched voltage and current and what is the load?