Define short-circuit current and explain its relation to Thevenin equivalents.

Define short-circuit current and explain its relation to Thevenin equivalents.

• A. I_sc is the current when the load is open-circuit; I_sc = V_th / R_th.
• B. I_sc is the current through the load at rated voltage.
• C. I_sc is the current through the output when the terminals are shorted; I_sc = V_th / R_th.
• D. I_sc is the current of the source when it delivers max power.

Answer: (C)

Short-circuit current is the current that flows when the output terminals are directly connected with zero resistance. In the Thevenin model, the network seen from the terminals is a voltage source V_th in series with a resistance R_th. When the terminals are shorted, the load resistance is zero, so the current is governed by Ohm’s law: I_sc = V_th / R_th. This is the current that flows through the short and through R_th, since they’re in series. Open-circuit means no current flows, so I_sc isn’t determined by an open load. The rating about delivering max power relates to choosing a load equal to R_th, not to a short. The current through the load at rated voltage isn’t specific to a short-circuit scenario either.

Short-circuit current is the current that flows when the output terminals are directly connected with zero resistance. In the Thevenin model, the network seen from the terminals is a voltage source V_th in series with a resistance R_th. When the terminals are shorted, the load resistance is zero, so the current is governed by Ohm’s law: I_sc = V_th / R_th. This is the current that flows through the short and through R_th, since they’re in series.

Open-circuit means no current flows, so I_sc isn’t determined by an open load. The rating about delivering max power relates to choosing a load equal to R_th, not to a short. The current through the load at rated voltage isn’t specific to a short-circuit scenario either.