Passive Sign Convention

Ideal Basic Circuit Element

• Has 3 attributes
  • Only two terminals, which are points of connection to other circuit components
  • Described mathematically in terms of current and/or voltage
  • Cannot be subdivided into other elements

Current

• Positive current flows from the positive terminal of a voltage source (active circuit element)
• Positive current will flow into the positive terminal of a resistor (passive circuit element)

Power

Whenever the reference direction for the current in an element is in the direction of the reference voltage drop across the element (as in the figure), use a positive sign in any expression that relates the voltage to the current. Otherwise, use a negative sign.

Interpreting

• Positive: Power is being delivered to the circuit element represented by the box. Or the circuit element is absorbing power
• Negative: Power is being extracted from the circuit element or the circuit element is supplying power, (additional book terminology – developed power).