Chapter 12 Flashcards
An SCR differs From an ordinary diode in that it passes significant current.
FALSE
It does not pass significant current, even when forward biased, UNLESS The anode voltage equals or exceeds the forward break over voltage. And when forward breakover voltage is reached, the SCR switch is on and becomes highly conductive.
Low current SCRs Can operate with an anode current of less than 1A.
TRUE
The size of an SCR decreases with an increase in current reading.
FALSE
It increases in size.
When an SCR is forward biased, it operates similar to a regular semiconductor diode.
FALSE
Reverse Bias
When an SCR is forward biased, there’s a small amount of forward leakage current called forward blocking current.
TRUE
When an applied voltage is above the forward breakover voltage (V sub BRS), the SCR fires or turns on.
TRUE
Increasing values of a forward bias can be used to reduce the amount of forward breakover
voltage if necessary to get an SCR to conduct.
TRUE
And SCR normally can be triggered into conduction by applying a pulse of control current to the gate.
TRUE
The correct method of turning off an SCR is to apply a proper signal to the gate of the SCR.
TRUE
Static turn on does not damage the SCR, provided the surge current is limited.
TRUE
The internal structure of an SCR consists of a PNP later.
FALSE
The internal structure consists of 2 PN junctions join together that form a PNPN layer.
The equivalent circuit analogy is used to understand a complex device.
TRUE
Equivalent circuit of an SCR is a circuit consisting of three interconnected PNP transistors.
FALSE
Is a circuit consisting of interconnected PNP and NPN transistors.
The most basic application of an SCR is a AC switch.
FALSE
DC Switch
3 SCRs are required for AC switching.
FALSE
2
Regular diodes cannot be used for AC and DC switching.
TRUE
An SCR can be turned on at different points in the conducting cycle.
TRUE
The proper operation of an SCR requires the correct mounting and cooling of the device.
TRUE
Press-fit SCRs are installed using the same procedure used for mounting and stud mounted diodes.
FALSE
The major advantages of using flat-pack and press-pack SCRs is the decreased surface area.
FALSE
The advantage of flat-pack and press-pack SCRa is the increased surface area available for thermal conduction.
A good technician can troubleshoot a light-sensing circuit by using signal substitution or circuit disturbances.
TRUE
An SCR can be triggered by shorting the anode to the gate.
TRUE
Information provided by manufactures on the installation of SCRs does not need to be followed.
FALSE
SCRs cannot be used in circuits to provide heat control.
FALSE
They can be used in heat control circuits.
An integrated circuit has an electronic component (SCR) and an electromechanical component (relay) in the same circuit.
FALSE
A Hybrid circuit
By using diodes, switches, and an SCR firing circuit, visual an audible alarms can be activated to serve as warning Signals.
TRUE
Unlike across the line starters, solid-state starters reduce inrush current.
TRUE
Solid state starters provide smooth, stepless acceleration in applications such as starting conveyors, compressors, and pumps.
TRUE
A typical solid-state starting circuit consists of starter and run contactors.
TRUE
And SCR cannot be used for overvoltage protection.
FALSE
And SCR can be used for overvoltage protection as a power supply protection circuit.
A _____________ Is a four layer PNPN semi conductor device.
SCR
An SCR uses a _____________ as an electrode.
Anode, cathode, gate
Silicone controlled rectifiers are used in power switching and _____________ circuits.
Phase control, battery charger, and inverter circuits.
Large SCR assemblies with many individual devices connected in series are used in _____________ converter stations.
High-voltage voltage DC
An uncontrolled method of turning on an SCR is a _____________ turn-on.
Voltage breakover, static, and thermal.
_____________ turn-on is the only correct way to turn on SCR.
Gate
_____________ turn on as a method of turning on an SCR when the voltage across the SCR terminals exceeds the maximum voltage rating of the device.
Voltage breakover
_____________ turn on is a method of turning on an SCR when a fast rising voltage is applied across the terminals of a triac.
Static
When a gate is pulsed or triggered in the proper forward-bias applied to the SCR, the _____________ regions close and the current begins to flow through the SCR.
Depletion
With _____________ control, the speed of a motor, the brightness of the lamp, and the output of an electric-resistance heating unit can be controlled.
Phase
A _____________ circuit is an SCR that has the ability to turn on at different points of the conducting cycle of a half-wave rectifier.
Half-wave phase control
When minimizing SCRs exposure to heat, a high temperature device, such as a _____________, should be shielded from radiating heat directly on the SCR case.
Lamp, power transformer, resistor.
The advantage of flat-pack and _____________ SCRs is the increased surface area available for thermal conduction.
Press-pack
The operations manual of the test instrument use when troubleshooting an SCR should be consulted for all measuring _____________.
Precautions, limitations, and procedures.
In addition to being used in light dimmers and speed controls, SCRs can be used in industry to control the power in _____________.
Battery chargers, power supplies, and machine tools.
Using a _____________ circuit, the control temperature can be maintained within 1°F over temperature range of 20°F to 150°F.
Bridge
An SCR can be used in circuits to provide _____________ for motor control, photo enlargers, and other times or delayed functions.
Time delay
The operation of a hybrid circuit begins with a switch in the _____________ position.
RESET
_____________ is a form of reduced voltage starting for standard motors.
Solid state starting
The heart of the solid-state starter is the _____________, which controls motor voltage, current, and torque during acceleration.
SCR
An _____________ characteristic curve shows the operating characteristics of an SCR when It’s gate is not connected.
Voltage-current
In the _____________ region, the resistance of the SCR is very small.
Forward avalanche
_____________ turn-on is a method of turning on an SCR with a proper signal is applied to the gate at the correct time.
Gate
The _____________ defines the level of voltage over a given time. That causes the device to turn on.
DV/DT Rating
A _____________ circuit is typically added across the SCR terminals to protect the SCR when static turn-on is a problem.
Snubber
_____________ turn-on is a method of turning on an SCR when heat levels exceed the limit of the SCR, typically 230°F.
Thermal
_____________ bias exists when the positive lead of the voltage source is attached to the cathode and the negative lead is attached to the anode.
Reverse
The _____________ and collector of each transistor represent the gate connection.
Base
_____________ is the control of the time relationship between two events when dealing with voltage and current.
Phase control
A _____________, like a heat sink, is an integral part of the heat transfer path of an SCR.
Mounting surface
The press-fit package is designed primarily for _____________ insertion into a slightly undersized hole in the heat exchanger (heat sink).
Forced
To mount a _____________ SCR, a whole may be punched in reamed in a flat plate, extruded and sized in sheet metal, or drilled and reamed.
Press-fit
Typically, _____________ SCRs fastened to heat sinks to ensure good heat flow.
Stud mounted
A _____________-pack SCR must be properly installed to provide Max with the heat transfer.
Press
The output of an SCR must be tested under operating conditions using a _____________.
Test circuit and and oscilloscope
Low power and some high power SCRs tested using an analog _____________.
Ohmeter
A _____________ circuit is a circuit that mixes mechanical devices and electronic devices in the same circuit.
Hybrid
A _____________ circuit is used to control the pulses to the gate.
Electronic triggering
________________ also provide smooth acceleration and minimize starting to work.
Solid state starters
A power supply protection circuit is often referred to as a ________________ circuit.
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