SCR operating states: Forward blocking condition During the forward blocking state of an SCR (thyristor), what are the typical anode-cathode voltage and current levels, respectively?
-
Ahigh and high
-
Blow and low
-
Chigh and low
-
Dlow and high
-
Emoderate and high
Answer
Correct Answer: high and low
Explanation
Introduction / Context:An SCR exhibits distinct operating states: forward blocking, forward conduction, and reverse blocking. Recognizing the voltage and current levels in each state is vital for protection and gating strategies.
Given Data / Assumptions:
- Anode positive with respect to cathode (forward bias).
- No gate trigger applied.
- Device is idealized to illustrate states (ignoring small leakage).
Concept / Approach:
In forward blocking, the SCR can withstand a high anode-to-cathode voltage but only a very small leakage current flows because the device has not been triggered into conduction.
Step-by-Step Solution:
Anode positive, gate off → junctions configured so device is non-conducting.Voltage: high (up to rated forward blocking capability).Current: low (leakage only).Verification / Alternative check:
Device datasheets specify forward blocking voltage ratings and leakage currents in this state.
Why Other Options Are Wrong:
High current would imply turn-on. Low voltage/low current corresponds to an off device with no applied forward voltage, not forward blocking capability.
Common Pitfalls:
Confusing forward blocking with latching/holding current concepts that apply once turned on.
Final Answer:
high and low