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*
