Electrical Engineering XYZ MCQs
Anode current in an SCR consists of:
- Either electron or holes
- Holes only
- Both electron and holes
- Electrons only
Correct answer: 2. Holes only
Explanation: An SCR (Silicon Controlled Rectifier) is a type of semiconductor device used in electronic circuits for switching and rectification purposes. It is a four-layer semiconductor device consisting of alternating P-type and N-type materials. An SCR has three terminals: Anode (A), Cathode (K), and Gate (G).
When a positive voltage is applied to the anode with respect to the cathode and a gate trigger signal is applied, the SCR becomes conductive. In its conductive state, current flows freely from the anode to the cathode.
Now, to understand the anode current in an SCR, it’s essential to grasp the behavior of charge carriers within the semiconductor layers:
- Electrons: In the N-type material, the majority charge carriers are electrons. When a forward bias is applied to the SCR (positive voltage on the anode), electrons flow from the N-type region towards the P-type region.
- Holes: In the P-type material, the majority charge carriers are holes. When a forward bias is applied, holes flow from the P-type region towards the N-type region.
In an SCR under forward bias conditions (anode positive with respect to cathode), both electrons and holes contribute to the flow of current. Electrons move from the N-type region towards the P-type region, while holes move from the P-type region towards the N-type region. This means that the anode current in an SCR consists of both electrons and holes.
Therefore, the correct option is “Both electron and holes.”