Silicon Controlled Rectifier Flashcards
What is an SCR?
Silicon Controlled Rectifier
The name “silicon controlled rectifier” is General Electric’s trade name for a type of ______.
Thyristor
SCRs are mainly used in electronic devices that reqire control of ____ voltage and power.
High
How many layers of semiconductors does an SCR have?
4 layers
Two structures formed within the SCR.
NPNP and PNPN
What are the junctions of an SCR?
J1, J2, and J3
What are the terminals of an SCR?
Anode, Cathode, Gate
What are the modes of operation for an SCR depending upon biasing?
Forward Blocking Mode
Forward Conduction Mode
Reverse Blocking Mode
Happens when anode is positive with respect to cathode and gate terminal is open.
Forward Blocking Mode
What junction can’t current pass through in forward bias, forward blocking mode?
J2
Two ways to bring SCR from blocking to conduction mode.
Increasing voltage between anode and cathode beyond the breakover voltage
Applying a positive pulse at the gate
The gate voltage required to maintain an SCR in the ON state.
0
The minimum current necessary to maintain SCR in the ON state.
Latching Current
A thyristor is brought from forward blocking mode to forward conducting mode by applying required ______.
Gate Voltage
Happens when negative voltage is applied to the anode and positive voltage to the cathode.
Reverse Blocking Mode
If forward voltage is increase in forward blocking mode, what happens to the J2 junction?
Avalanche Breakdown
An SCR incapable of blocking reverse voltage.
Asymmetrical SCR or ASCR
Typical reverse breakdown rating of an ASCR
Tens of Volts
Reverse conducting diodes used to fabricate ASCRs
RCT or reverse conducting thyristor
Thyristor Turn On Methods
Forward-Voltage Triggering
Gate Triggering
Dv/Dt Triggering
Temperature Triggering
Light Triggering
Occurs when the anode-cathode forward voltage is increased with the gate circuit opened.
Forward-voltage triggering
Occurs when the thyristor should be in forward blocking state where the applied voltage is less than the breakdown voltage.
Gate Triggering
Occurs when the width of depletion region decreases as the temperature is increased
Temperature Triggering
During a rudimentary test of SCR, where do you put the red test lead?
Gate
During a rudimentary test of SCR, where do you put the black test lead?
Cathode
What should the ohmmeter show when doing a rudimentary test of SCR?
Continuity/OL
“Normal” SCRs that are lacking an internal resistors are sometimes referred to as _____.
Sensitive Gate SCRs
A circuit that consists of an SCR placed in parallel with the output of a DC power supply, for placing a direct short-circuit on the output of that supply to prevent excessive voltage from reaching the load.
Crowbar
The electron tube version of an SCR
Thyratron
An SCR that is specifically designed to be turned off by means of reverse triggering.
Gate-Turn-Off Thyristor (GTO)
Thyristors are mainly used in devices where the control of ____ power, possibly coupled with ____ voltage is demanded.
high, high
It is the minimum forward voltage, gate being open, at which SCR starts conducting heavily.
Breakover Voltage
Commercially available SCRs have what range of breakover voltages?
50V to 500V
It is the maximum reverse voltage that can be applied to an SCR without conducting in the reverse direction.
Peak Reverse Voltage
It is the maximum anode current, gate being open, at which SCR is turned off from ON conditions.
Holding Current
Commercially available SCRs have PRV ratings up to ___.
2.5kV
It is the maximum anode current that an SCR is capable of passing without destruction.
Forward Current Rating
Commercially available SCRs have forward current ratings of ___.
30A to 100A
Indicates the maximum forward surge current capability of SCR.
Circuit Fusing Rating
The ____ the firing angle, the ____ is the average current.
greater, smaller
