Voltage Sources
A voltage source is any device capable of producing an electrical potential difference between two terminals. This potential difference pushes electrons through a circuit, allowing electrical current to flow and electronic devices to operate.
What is a Voltage Source?
A voltage source is a device that supplies electrical energy by maintaining a voltage between its positive and negative terminals.
When connected to a complete circuit, the voltage source provides the force needed to move electrons through the circuit.
Why Voltage Sources are Important
Without a voltage source, electrical circuits cannot operate.
Every electronic device—from a small calculator to a large industrial machine—requires a source of electrical energy.
The voltage source provides the energy needed for components such as resistors, LEDs, transistors, integrated circuits and motors.
Types of Voltage Sources
The most common voltage sources are:
| Voltage Source | Produces |
|---|---|
| Battery | Chemical Energy → Electrical Energy |
| Generator | Mechanical Energy → Electrical Energy |
| Solar Cell | Light Energy → Electrical Energy |
| Power Supply | AC Mains → Regulated DC |
| Fuel Cell | Chemical Energy → Electrical Energy |
Batteries
Batteries are among the most common voltage sources. They produce electricity through chemical reactions occurring inside their cells.
Examples include:
- AA and AAA batteries (1.5 V)
- 9 V batteries
- Lithium-ion batteries (3.7 V nominal)
- 12 V lead-acid car batteries
- Rechargeable NiMH batteries (1.2 V)
Power Supplies
Electronic power supplies convert the AC voltage from the electrical mains into stable DC voltages suitable for electronic equipment.
Common output voltages include:
- 3.3 V
- 5 V
- 9 V
- 12 V
- 24 V
- ±15 V for analogue circuits
Modern power supplies may be linear or switch-mode (SMPS).
Generators
Generators produce voltage by electromagnetic induction.
When a conductor moves through a magnetic field, or when the magnetic field changes around a conductor, a voltage is induced.
Examples include:
- Power station generators
- Portable generators
- Vehicle alternators
- Bicycle dynamos
Solar Cells
Solar cells convert sunlight directly into electrical energy using the photovoltaic effect.
A single silicon solar cell typically produces about 0.5 to 0.6 volts.
Multiple cells are connected in series to obtain higher voltages.
Ideal and Practical Voltage Sources
In electronics, voltage sources are often classified as either ideal or practical.
| Ideal Voltage Source | Practical Voltage Source |
|---|---|
| Constant voltage under all conditions | Voltage drops slightly under load |
| No internal resistance | Has internal resistance |
| Theoretical model | Real-world devices |
All real batteries and power supplies have some internal resistance.
Voltage Source Polarity
Every DC voltage source has two terminals:
- Positive (+)
- Negative (−)
Correct polarity is important when connecting electronic circuits. Reversing the polarity may damage sensitive electronic components.
Applications
Voltage sources are found in almost every electrical and electronic system.
- Mobile phones
- Computers
- Audio amplifiers
- Televisions
- Arduino and ESP32 projects
- Industrial automation
- Medical equipment
- Electric vehicles
Key Points
- A voltage source provides the electrical energy needed to operate a circuit.
- Batteries use chemical reactions to generate voltage.
- Generators produce voltage through electromagnetic induction.
- Solar cells convert sunlight into electricity.
- Power supplies convert AC mains into regulated DC voltages.
- All practical voltage sources have internal resistance.