Master the Basics: Ideal vs. real-world power sources

When designing electronic circuits, it’s common to assume that power sources like batteries or wall adapters are ideal—meaning they always supply a perfectly constant voltage, no matter what’s connected to them. This simplifies circuit analysis and makes it easier to do calculations.

For example, if you're designing a project powered by a 9V battery, you might assume there's always exactly 9 volts between its terminals. That’s a helpful simplification—but in reality, power sources don’t behave perfectly.

Ideal Assumptions Work—Until They Don’t

If you're powering something simple, like an LED that draws only a few milliwatts, then assuming a constant 9V from your battery is fine.

But if you try to power something much larger—like a motor in an electric car—that same battery won't hold up. Even if the motor only required 9 volts, the battery would fail because it can’t deliver the massive amount of current the motor needs.

Real-World Limitations of Power Sources

Every real power source has a limit to how much current it can supply at its rated voltage. Let’s say your 9V battery can safely provide 1 amp of current. That doesn't mean it will always push out 1 amp—current depends on the load it's connected to, following Ohm’s Law.

For example:

• If your load is 10,000 ohms, the current draw would only be 0.009 amps (9 milliamps). That’s no problem for the battery.

• But if your load is 2 ohms, it would require 4.5 amps to maintain 9V across the load. That’s more than the battery can safely provide, which could cause overheating or voltage drop.

Analogy: Power Source as a Muscle

Think of a battery like your arm. Maybe you can lift a 10-pound dumbbell comfortably. But if you try to lift 50 pounds, you might strain your muscles or even get hurt. Similarly, when a battery is overloaded, it gets hot and can't maintain its output voltage. The result? Your circuit doesn’t get the power it needs.

Power Adapters Have Limits Too

Even AC-to-DC adapters have defined limits. For example, a USB power adapter may state:

• Output: 5V, 2A

That means it will supply a steady 5 volts for devices that draw up to 2 amps of current. Multiply the voltage and current, and you get:

• 5V × 2A = 10 watts

So this adapter can deliver up to 10 watts of power—anything more would exceed its limits and could cause performance issues.

Key Takeways

While it’s okay to treat power sources as ideal during the early design phase, always remember to check their real-world limitations before connecting high-power loads. Knowing the maximum current and wattage a source can handle helps you design safe, reliable circuits—and protects your components from damage.