LDO Dropout & Power Dissipation Calculator
Dropout headroom, power dissipation and efficiency for a linear (LDO) regulator.
Input
ℹ A linear regulator burns the voltage difference as heat: P = (Vin−Vout)·Iload.
Results
Dropout Headroom—
Power Dissipation—
Efficiency—
💡 Usage & Formula
P = (Vin−Vout)·Iload + Vin·Iq; efficiency ≈ Vout/Vin. Dropout headroom must exceed the regulator's spec.
When you need it: Checking whether an LDO has enough headroom to stay in regulation, and how hot it runs, at your input voltage and load current.
Worked example: 5 V→3.3 V at 200 mA dissipates (5 − 3.3) × 0.2 = 0.34 W. In a SOT-23 (θJA ≈ 200 °C/W) that's a 68 °C rise — near the limit, so use a larger package or a buck pre-regulator.
Tips & gotchas:
- LDO efficiency is just
Vout/Vin— the rest becomes heat, so keep Vin close to Vout. - Respect the dropout voltage at your maximum current, or the output sags out of regulation.
- Output-capacitor ESR requirements vary — some LDOs need a minimum ESR, others demand low ESR; check the datasheet.
- For a big step-down at high current, a switching regulator wastes far less power than any LDO.
📖 References:LDO regulator (Wikipedia)