Specials Diodes Flashcards
What does SCR stand for?
Silicon Controlled Rectifier
What kind of feedback does SCR use?
uses Regenerative feedback
What is Regenerative Feedback?
part of the output is returned to the input to reinforce the input power
How many layers are in an SCR and what are the materials?
four layers and alternating p-type and n-type material
what are the three electrodes of an SCR
- Anode
- Cathode
- Gate
What direction is an SCR?
undirectional device
Is SCR current or voltage operated?
current operated
Can an SCR control and switch AC and/or DC power
YES
Does SCR rectify AC or DC
AC
SCR
What is lathing current?
current must be applied to start conduction
SCR
What is holding current?
current must be maintained for SCR to remain in conduction
SCR
What is Voltage Break Over(VBO)
forward voltage that puts SCR into conduction
SCR
What is Voltage Break Over(VBO)
the forward voltage required to put SCR into conduction
SCR
What is Voltage Break Over(VBO)
the forward voltage that puts SCR into conduction
What is the structure of the SCR
consists of two PN junctions to form a PNPN Layer
What is the normal state for SCR
Forward Blocking State
The forward blocking state allows the SCR to conduct if one of the two conditions apply
- Exceed VBO
2.Apply a gate voltage
The 3 conditions Required to gate “on” the SCR
- must be positive anode
- must be negative cathode
- gate must be positive compared to the cathode and have a 1.4 v knee voltage
The 4 conditions needed to turn off SCR
- install a switch on Anode
- Install shorting wire from anode to cathode
- put a negative signal on the gate
- drop holding current below L.C.D
Condition Required to Turn on Triac
Negative on Terminal 1, Positive on Terminal 2, Positive on the gate with last least 1.5v potential to T1 and T2
The condition required to turn off Triac
drop load current below holding current
The Triac can be triggered into ______ in _____ direction by a gate ____ in either direction
conduction, either, current
what could a Triac be replaced with
a mechanical cut-out switch
A pair of Triacs and replace ______ contactors on a permanent ____ capacitor motor
reversing, split
what instrument is used to make a rough test of a trial?
ohmmeter
(TESTING)What should you see when the gate of Triac is open?
high ohms
(TESTING)what should you see when the gate of the Triac is energized?
continuity
What direction is a Diac
Bidirectional
Does a Diac have a gate?
No
Does a Triac have a gate?
Yes
How does conduction initiate on Diac
when Voltage Break Out (VBO) is exceeded
condition to turn off Diac
by dropping load current below holding current
what does the Diac ensure the triac does not do?
ensures triac doesn’t turn on by spikes in the line
How many layers in a Diac?
three layers
Unlike the transistor, the junctions are _____ and _____ doped
heavily and equally
Diacs are primarily used as a ______ device
Triggering
When using an Ohmmeter to test a disc the resistance will be ______ when the disc is good
high in both directions
Photo Cells are _______ devices
Light-Operated
Photo Cells - when there is no light, resistance is _____
High
Where are Photo Cells used
where time response is not critical
what appliances are photoconductive cells often used on
large gas appliances
Photo Diode is ____ operated
Light
Photo Diode - No light means resistance is _____
High
Photo Diode - operated in _______ bias mode
Reverse
Do photo diodes exhibit fast or slow response time?
Fast
