Thyristor & Power Control Circuits Test
In a half wave triac has a conduction angle of?
0 to 90 degrees
When an SCR is turned on, The anode-cathode voltage (Vak) reads approximately?
1.0 vdc
An SCR that is turned on (conducting has an anode-cathode voltage drop (Vak) of approximately?
1.0v
In a halfwave circuit with an RC 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 citcuit, RMS power to the load is decresed by?
A decrease in the conduction angle of the load signal
The 3 terminals of an SCR are?
A,K, and G
A triac is desirable in AC power control because it can conduct with?
All of the above
In a power control application, an SCR may be required to act as the?
All of the 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 anount of time an SCR conducts in electrical degrees is described 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 conduction
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 gates 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
For an SCR to turn on, The?
Gate has to be more positive then the cathode
Phase control is achieved 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 tirac
For an SCR to turn off, the gate?
Has nothing to do with the SCR turn off
Small changes in gate voltages that turn on an SCR can cause?
Large changes in load voltage
A half wave rectifier delivers?
Less power to the load per cycle then 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
A unijunction transistor?
One PN junction
An SCR used as a half wave rectifier conducts?
Only on positive alternations of an AC signal
The minimum emitter voltage needed to cause the UJT to fire is the?
Peak-Point emitter voltage
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
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 cycles 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 thyristor 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 on the thyristor 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 full-wave 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
