What is Voltage Drop?
Voltage drop is the reduction in voltage that occurs as electric current flows through a component or conductor. Every resistor, wire, LED, motor and electronic component causes some voltage to be lost as current passes through it.
What is Voltage Drop?
A voltage drop is the difference in electrical potential between two points of a circuit caused by current flowing through resistance.
Whenever current flows through a resistor, wire or electronic component, part of the source voltage is used by that component.
In other words, every component "uses up" a portion of the available voltage.
Water Pipe Analogy
Imagine water flowing through a long pipe.
- The water pressure is highest at the pump.
- As water flows through valves and restrictions, pressure decreases.
- The pressure lost is similar to voltage drop.
Likewise, as electric current flows through circuit components, the voltage gradually decreases.
Why Does Voltage Drop Occur?
Voltage drop occurs because every conductor and every electronic component has some resistance.
As electrons move through that resistance, electrical energy is converted into other forms of energy such as:
- Heat
- Light
- Mechanical motion
- Sound
- Magnetic energy
Examples of Voltage Drop
| Component | Typical Voltage Drop |
|---|---|
| Silicon Diode | ≈ 0.7 V |
| Schottky Diode | ≈ 0.2–0.4 V |
| Red LED | ≈ 1.8–2.2 V |
| Blue LED | ≈ 3.0–3.5 V |
| Copper Wire | Very small (depends on length and current) |
Voltage Drop Across a Resistor
When current flows through a resistor, a voltage appears across its terminals.
The larger the resistance or the larger the current, the greater the voltage drop.
This relationship is described by Ohm's Law:
V = I × R
Where:
- V = Voltage (volts)
- I = Current (amperes)
- R = Resistance (ohms)
Kirchhoff's Voltage Law
One of the most important rules in electronics states:
The total voltage supplied by the source is equal to the sum of all voltage drops around a closed circuit.
Example:
- Battery = 12 V
- Resistor 1 = 4 V drop
- Resistor 2 = 3 V drop
- LED = 2 V drop
- Motor = 3 V drop
Total voltage drop:
4 V + 3 V + 2 V + 3 V = 12 V
Voltage Drop in Wires
Even copper wires have resistance.
When large currents flow through long wires, a noticeable voltage drop can occur.
This can cause:
- Dim lights
- Slow motors
- Reduced amplifier performance
- Lower charging voltage
- Power loss
For this reason, high-current circuits often use thicker cables to reduce resistance.
Measuring Voltage Drop
Voltage drop is measured using a digital multimeter set to the voltage range.
Place one probe on each side of the component while the circuit is powered.
The reading obtained is the voltage drop across that component.
Practical Examples
| Circuit | Voltage Drop |
|---|---|
| LED current-limiting resistor | Several volts |
| Power transistor | Depends on operating conditions |
| Bridge rectifier | ≈ 1.2–1.4 V (two conducting diodes) |
| Speaker cable | Very small if correctly sized |
| Battery cables | Should be kept as low as possible |
Key Points
- Voltage drop is the reduction in voltage caused by current flowing through resistance.
- Every component in a circuit produces some voltage drop.
- Voltage drop represents electrical energy being converted into other forms.
- Long or thin wires create larger voltage drops.
- Voltage drop is measured across a component using a voltmeter.
- The total voltage drops in a circuit equal the source voltage.