Question 1

The capacitor cannot charge until the triac turns off at the end of the half cycle of alternating current.

Accepted Answer

The capacitor can only charge when the triac is turned on, allowing current to flow through it. When the triac turns off, the capacitor is isolated from the power source and can no longer charge.

Question 2

As long as the triac is conducting, there is only about ____ applied to the phase-shift circuit.&#10;A) 1 volt&#10;B) 2 volts&#10;C) 3 volts&#10;D) 4 volts

Accepted Answer

When a triac is conducting, it behaves like a closed switch with a very small voltage drop across it, typically around 1 volt, which is the amount applied to the phase-shift circuit in this scenario.

Question 3

The UJT can be used to supply the trigger pulses for the triac that needs both negative and positive pulses.

Accepted Answer

False

Question 4

The device most often used to phase shift the triac is the ____.&#10;A) SCR&#10;B) diac&#10;C) diode&#10;D) sink

Accepted Answer

The diac is most often used to phase shift the triac because it can trigger the triac by switching on when a certain voltage threshold is reached, allowing for controlled phase shifting in AC circuits.

Question 5

The diac is most commonly referred to as a ____ device.&#10;A) phase-shifted&#10;B) bilateral&#10;C) unidirectional&#10;D) bipolar

Accepted Answer

The answer of The diac is most commonly referred to...

Question 6

The UJT is an AC operated device.

Accepted Answer

The UJT (UniJunction Transistor) is primarily used as a triggering device for SCR's and is not specifically an AC operated device; it is more commonly associated with pulse generation and timing circuits in DC applications.

Question 7

To phase shift the triac, separate the ____ from the voltage applied to MT₁ and MT₂. A) gate currents B) gate grounds C) gate pulses D) gate sinks

Accepted Answer

To phase shift the triac, it's necessary to separate the gate pulses from the voltage applied to the specific components mentioned. This is because the timing of these gate pulses controls the phase angle at which the triac is triggered, thus adjusting the phase shift.

Question 8

The triac, like the SCR, must be phase shifted if complete control is to be gained over the AC voltage applied to it.

Accepted Answer

The triac, similar to the SCR, requires phase shifting to achieve complete control over the AC voltage applied to it because it allows for control of the point within the AC cycle at which the triac is triggered, thereby controlling the amount of power delivered to the load.

Question 9

Since the triac is essentially two SCRs, when it fires in one direction, the voltage drop across the device becomes about ____.&#10;A) 1 volt&#10;B) 2 volts&#10;C) 3 volts&#10;D) 4 volts

Accepted Answer

When a triac fires, it behaves like two SCRs in parallel, and the voltage drop across it is typically around 1 volt, similar to a single SCR.

Question 10

The charge time of the capacitor is determined by the size of capacitor and the amount of resistance connected in series with it.

Accepted Answer

The charge time of a capacitor is determined by the product of the capacitance (size of the capacitor) and the resistance connected in series with it, known as the time constant (τ = RC).

Deck 25: Phase Shifting the Triac