Overview
This lecture covers voltage and current sources, their symbols, the distinction between independent and dependent sources, and example problems related to interpreting and calculating voltages and power in circuits.
Voltage and Current Sources
- Two main types of sources: voltage sources and current sources.
- Symbols: both use circles; voltage sources have + and - signs, current sources use an arrow for direction.
- Voltage source values are labeled as V (e.g., 10V); current source values as I (e.g., 1A).
- Voltage sources can also be represented with battery symbols (unequal lines for + and -).
- Most circuits commonly use voltage sources.
Independent and Dependent Sources
- Independent sources provide fixed voltage or current unrelated to other circuit elements.
- Dependent (or controlled) sources have values that depend on another voltage or current in the circuit.
- Dependent source symbols use diamonds; label shows their dependence (e.g., kVx, kIx).
- Four types of dependent sources:
- Voltage source, voltage dependent (V = kVx)
- Voltage source, current dependent (V = kIx)
- Current source, current dependent (I = kIx)
- Current source, voltage dependent (I = kVx)
- Dependent sources often appear in transistor models.
Circuit Examples and Measurements
- Connecting a load in parallel to a voltage source means the load voltage equals the source voltage.
- Reversing probe polarity measures negative voltage.
- The current provided by a voltage source depends on the load; exceeding source ratings can lower output voltage.
- Power across a load: P = V × I.
- If calculated power is positive, the element absorbs power; if negative, it supplies power.
- Power sources (like rechargeable batteries) can sometimes absorb power during charging.
Key Terms & Definitions
- Independent Source — Supplies a fixed voltage or current regardless of other elements.
- Dependent Source — Source whose value depends on another voltage or current in the circuit.
- Parallel Connection — Both terminals of two elements are connected, resulting in equal voltage.
- Absorbing Power — When an element consumes (positive) electrical power.
- Supplying Power — When an element delivers (negative) electrical power.
Action Items / Next Steps
- Practice drawing circuit symbols for voltage and current sources (independent and dependent).
- Solve example problems involving dependent sources and power calculations.
- Review concept differences between parallel and series connections.