Key Takeaways
- Resistor divider is simple but extremely inefficient (≤50%)
- All wasted power becomes heat, requiring thermal management
- Buck replaces resistor with a switch — ideal efficiency approaches 100%
Lesson 1
Why Not Use a Resistor Divider?
The most intuitive way to reduce voltage is a resistor divider, but it has a fatal flaw: too much power loss.
Suppose you have a 12V supply and need to provide 6V to a load. The simplest idea: put an equal resistor in series to divide the voltage in half.
The problem: the divider resistor dissipates as much power as the load! If the load needs 3.6W, the resistor wastes another 3.6W. Efficiency is only 50%, and all wasted energy becomes heat.
For power-sensitive applications like phones, laptops, and EVs, this is unacceptable. We need a way to step down voltage with almost no energy waste — that's why Buck converters exist.
The core idea of Buck: use a 'switch' instead of a 'resistor' to regulate output voltage. An ideal switch has no voltage drop when on and no current when off, so theoretically it dissipates zero power. Efficiency can exceed 90%.
Resistor Divider: Simple but Inefficient
VIN=12V, R1=R2=10Ω. Output is 6V, but R1 wastes half the power.
After reading this section, run the simulation and observe the waveforms. To explore further, open the example in a standalone page.
Watch Items
- Observe the voltage and current on the divider resistor — their product is the wasted power
- Think: if load current increases, how does the waste in the resistor divider change?