Controlled Rectifiers Flashcards
how many degrees does a SCR Conduct for?
180°
a triac can be turned off by reversing the polarity of the pulse to the gate?
(T or F)
False
what is the difference between a triac and SCR?
current in the triac is bi-directional
what is a diac mainly for?
trigger triac
a SCR conducts current in how many directions?
1
when more load is added to a cap filtered cct the percent ripple would? (increase, decrease)
increase
what conditions must exist in order to properly trigger a silicon controlled rectifier?
- forward bias
2. positive gate pulse
what are 3 ways to turn off (commutate) an SCR?
- natural
- forced
- frequency or AC
in a class B fire alarm system what are the three conditions of a smoke detector?
- normal(low current 10-13 mA)
- trouble (no current)
- alarm (high current)
FA+CA=180°. FA=R×C T or F
true
what is the current limit of a triac?
40mA
what is the typical breakover voltage of a DIAC?
(+/- ) 30Volts
what is the name of a cct used to prevent undesirable triggering of an SCR due to dv/dt?
RC snubber
what is commutation of an SCR?
turning off the SCR
what is the name of the process of controlling the average voltage with an SCR?
phase contol
what is the name of a rectifier that is made by replacing two diodes in a bridge rectifier with two SCRs
a controlled bridge rectifier (hybrid)
what does an AVR do
controls the output voltage of an alternator
in an RC timing trigger circuit what controls the capacitor charge rate
a variable resistor
why do additional pulses within a cycle not have an effect on the SCR
the SCR is already triggered and is conducting
what is the purpose of the isolation Transformer in a pulse trigger circuit
to isolate the low voltage trigger circuit from the higher voltage SCR circuit
what are the advantages of using SCRs over conventional controlling or switching methods
no arcing,
no moving parts,
less power dissipated
which device acts like two SCRs connected in a inverse parallel configuration
Traic
what is the recommended method of triggering an SCR
positive gate pulse
what are three undesirable methods of triggering an SCR
- exceeding break over voltage
- fluctuations in voltage
- temperature changes
