Thyristor and Power Control (Test 7)

In a half wave triac has a conduction angle of

0 to 90 degrees

When a scr is turn on, the anode-cathode voltage(Vak) reads approximately

1.0Vdc

An scr that is turned on (conducting has an anode-cathode voltage drop(Vak) of approximately)

1.0v

In a half wave circuit with a diode network at the gate of the scr, the phase control range is approx.

180 to 0 degrees

In how many triggering modes can a triac operate

4

In a phase control circuit, rms power to the load is decreased by

A decrease in the conduction angle of the load signal

The terminals of an scr are

A, K and G

A triac is desirable in ac power control because it can conduct with

All of above

In a power control application, an scr may be requires to act as the

All of above

When the scr is turned on, actual anode-cathode voltage depends primarily

Anode current

The anode current of an scr is limited by the

Anode resistor

Anode current in an scr can be determined by the

Anode resistor value and the anode resistor voltage

A triacs conduction can be described as

Bidirectional

The only junction of an scr that measures like a normal diode is the

Cathode-gate junction

The amount of time an scr conducts in electrical degrees is decribed as the

Conduction angle

For an SCR, a small gate voltage can

Control a large anode-cathode voltage

Decreasing the conduction angle

Decreases the average voltage across the load

In a triac full-wave phase control circuit, power is delivered to the load

During both half cycles when the triac is conducting

In a full wave phase control circuit, power is delivered to the load

During both half-cycles when the scr is triggered

The three terminals of ujt are

E, B1 and B2

When testing an scr with a multimeter, you read overload or high resistance in either polarity between the gate and the cathode terminals, the problem could be

Either a or b

In order to conduct an scr has to be

Forward biased, gate to cathode

An scr has

Four layers arranged as PNPN

Phase control is achived in triac circuits by supplying the gate and load with the same sc source signal and by adjusting the amplitude of the

Gate signal to control the conduction time of triac

For an scr to turn off, the gate

Has nothing to do with scr turn off

A half wave restifier deliver

Less power to the load per cycle than a full wave rectifier circuit does*

A triac turns on when a proper gate trigger voltage is applied, the triac turns off when

Load signal drops below the voltage needed to supply holding current (iH) to the triac

In a triac, mt1 is an abbreviation for

Main terminal 1

Holding current (iH) in an scr is the

Minimum anode current required to keep the scr conducting*

Is power to the load continuous for a full wave rectifier circuit

No power is delivered to the load for most full cycle but not all of it*

A floating ground is a circuit common that is

Not connected to earth ground

An unijunction transistor

One PN juction

An scr used as a half wave rectifier conducts

Only on positive alternations of an ac signal

The minimun emitter voltage needed to cause the ujt to fire is the

Peak-point emitter voltage (vP)

Controlling the phase in a power control circuit is desirable because

Phase control allows for further adjustment of power delivered to the load beyond simple full wave and halfwave rectification

A triac with a gate trigger voltage supplied will conduct

Positive or negative voltages

Which of the following statements is true of scr phase control

Power can be controlled to a load

The output signal of a ujt at B1 is a

Pulse

When an scr controls a half wave rectifier, what must be supplied during the negative half cycle for the scr to maintain conduction on each positive half cycle

Scr holding current

A triac operates much more like two inversely parallel

Scr's

Parameters unique to a particular tryristor can be found on the manufactures

Specification sheet

Specific scr holding current can be determined from the value of

The anode resistor voltage divided by the anode resistor value

An scr is a

Thyristor

Phase retard means delaying the phase of the

Trigger with respect of the anode voltage

The Thyristor circuits ont he tryristor and power control circuits board should be modified with

Two-post connectors

A ujt is a

Voltage controlled device

An scr is a

Voltage controlling device

An scr conducts for less than the 180 degrees for each half cycle of a fullwave rectified because the bridge rectifier does not conduct

When the source (Vac) is less than the voltage required for forward bias of the scr and rectifier diodes

For an scr to turn on, the

gate has to be more positive than the cathode*

Small changes in gate voltages that turn on an scr can cause

large changes in load voltage*