Electronics; Controlled Rectifiers Objective 1 Flashcards
When are tab style SCRs typically used?
Low current circuits from 2 amps to 20 amps
What “family” of electronic devices do SCRs belong?
Thyristor
The threaded stud is generally the __________ (anode/cathode/gate) on most SCRs
Anode
What kind of SCR is usually used in medium power circuits?
Stud mount SCRs
What type of SCR is generally used for very large power circuits?
Hockey puk
What is the threaded stud of a stud mount SCR connected to?
Directly to the heat sink
What happens when an SCR gets too hot?
Break over voltage will be reduced
What ate heat sinks usually made of?
Aluminum
What does silicon grease do in an SCR application?
Provides heat transfer from SCR to heat sink
What is the gate of an SCR connected to?
A triggering circuit that controls the SCR
What does triggering an SCR mean?
Current pulse applied to gate to make it start conducting
What is gating or firing?
Another names for triggering
What is commutation with regards to SCRs
Turning off
When can an SCR trigger?
1) when its forward biased (anode positive with respect to cathode)
2) current pulse applied from gate to cathode (gate positive with respect to cathode)
How long does an SCR stay turned on?
As long as the current from anode to cathode is equal to or greater than a specified value. (HOLDING CURRENT)
What is the holding current value for most SCRs?
1mA per ampere of the rated anode current
I(t(av))
How long is a positive current pulse?
10 microseconds
How much current is required in a “positive current pulse” to turn on an SCR?
5× the minimum gate current rating
What normally dictates the value of gate current?
The current rating of the SCR
What can be used to prevent gate burnout from excess current?
Resistor in series with the gate
How can you accidently trigger an SCR?
Exceed breakover voltage
Fluctuations in voltage
Temperature changes
What is an RC snubber circuit?
Paralleled resistor and capacitor used to limit the rate at which the voltage can increase
What is dv/dt
Rate of change of voltage
At what voltage could an SCR falsely gate?
0.7V
What is the problem with heat in semiconductor devices?
Heat can cause leakage current
How much leakage current can result from a 10°C of temperature rise?
Leakage current doubles
What happens when leakage current = gate current?
Scr will turn on
At what point is breakover voltage reached when gate current is provided?
Gate voltage is never reached in this situation
What is the dynamic repetitive maximum?
The maximum or peak operating voltage
