Question 1

If the variable resistor is adjusted so that the gate current leads the voltage by a greater amount, the SCR fires later.

Accepted Answer

When the gate current leads the voltage by a greater amount, the SCR fires later because the gate current needs to reach a certain threshold before the SCR can fire. If the gate current is leading the voltage by a greater amount, it will take longer for the gate current to reach the threshold, and therefore the SCR will fire later.

Question 2

One of the simplest ways to phase shift an SCR is to use a ____ to provide trigger circuit isolation from the line.&#10;A) large edge-tapped transformer&#10;B) small edge-tapped transformer&#10;C) large center-tapped transformer&#10;D) small center-tapped transformer

Accepted Answer

A small center-tapped transformer is commonly used to provide trigger circuit isolation from the line in the context of phase shifting an SCR, as it offers a compact and efficient means of achieving the necessary isolation and control.

Question 3

____ means to change the phase of one thing in reference to another.&#10;A) Hand shifted&#10;B) Phase shifted&#10;C) Power shifted&#10;D) Current shifted

Accepted Answer

Phase shifting refers to the process of changing the phase of one waveform in relation to another, which is commonly used in signal processing and electrical engineering.

Question 4

The ____ determines the amount of phase shifting.&#10;A) variable resistor&#10;B) variable semiconductor&#10;C) constant resistor&#10;D) variable transformer

Accepted Answer

The variable resistor, often used in circuits like phase shifters, can adjust resistance, thereby affecting the phase angle of the signal passing through.

Question 5

As long as the voltage applied to the gate of the SCR is locked in phase with the voltage applied to the anode, the SCR cannot be fired after the AC voltage applied to the anode has reached ____&#176;.&#10;A) 15&#10;B) 45&#10;C) 90&#10;D) 180

Accepted Answer

The SCR cannot be fired after the AC voltage applied to the anode has reached 90° because at this point, the voltage starts to decrease, reducing the forward bias and thus the ability to turn on the SCR.

Question 6

An SCR that has not been phase shifted has the voltage, which is applied to the gate locked in phase with the voltage applied to the anode.

Accepted Answer

In an SCR (Silicon Controlled Rectifier) without phase shifting, the gate voltage is indeed in phase with the anode voltage, meaning they reach their maximum, minimum, and zero points simultaneously. Phase shifting would alter this synchronization to control the firing angle and hence the power delivered to the load.

Question 7

To obtain full control of the AC half cycle applied to the anode, the voltage applied to the gate must be in-phase with the voltage applied to the anode.

Accepted Answer

To obtain full control of the AC half cycle applied to the anode, the voltage applied to the gate does not need to be in-phase with the voltage applied to the anode; it only needs to be sufficient to trigger the device at the desired point in the AC cycle.

Question 8

By choosing the correct values of resistance and capacitance, the voltage applied to the load can be controlled from ____.&#10;A) 0 to half its value&#10;B) 0 to its full value&#10;C) 0 to its double value&#10;D) half its vault to its full value

Accepted Answer

By properly selecting the resistance and capacitance values in a circuit, it is possible to control the voltage applied to the load from 0 to its full value. This is achievable through various circuit configurations, such as using a variable resistor (potentiometer) or implementing pulse-width modulation (PWM) techniques with capacitors and resistors to adjust the effective voltage seen by the load.

Question 9

In order for an SCR to gain complete control of the waveform it must be phase shifted.

Accepted Answer

An SCR is a phase-controlled device, meaning that the point in the AC waveform at which it turns on can be controlled by varying the phase of the gate signal. This allows the SCR to control the amount of power that is delivered to the load.

Question 10

An SCR that has not been phase shifted can control all of the positive waveform.

Accepted Answer

An SCR (Silicon Controlled Rectifier) without phase shifting cannot control the entire positive waveform; it can only control the portion of the waveform after it is triggered.

Deck 19: Phase Shifting an Scr