Electrical & Electronics
Linear Regulator & LDO Calculator
Estimate linear-regulator power loss, efficiency, dropout margin, junction temperature and load limits.
Your inputs
Your results
- Regulator dissipation
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- Estimated efficiency
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- Dropout margin
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- Junction temperature estimate
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- Temperature margin
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- Maximum load within entered limits
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—Check regulator dropout and heat separately
Estimate linear-regulator loss, efficiency and junction temperature for an entered load. Compare dropout, current and thermal limits independently. These are steady-state estimates from supplied assumptions, not a device-specific regulation or transient model.
Step by step
- Enter input and desired output voltages, load current and quiescent current with their displayed units.
- Enter dropout, current limit, ambient temperature, junction limit and thermal resistance from relevant device conditions.
- Inspect every limit warning and the maximum-load estimate, not only voltage headroom.
Settings and limits
- Dropout assumption
- Dropout margin compares available voltage with the entered requirement. Real dropout depends on current and temperature.
- Quiescent current
- The model counts quiescent current drawn from the input in power loss and efficiency. Check the device's definition.
- Thermal resistance
- Use a θJA appropriate to the package, board and cooling. A typical datasheet value may not describe your layout.
Worked example
The lower-load example passes the entered limits. Its junction temperature includes both load loss and quiescent power.
Example input
Vin = 12 V; Vout = 5 V; Iq = 50 µA
Vdropout = 0.3 V; Ilimit = 500 mA
TA = 25 °C; TJmax = 125 °C; θJA = 50 °C/W| Iload | Pd | TJ | TJmax − TJ | Imax |
|---|---|---|---|---|
| 100 mA | 0.7006 W | 60.03 °C | 64.97 °C | 285.628571 mA |
| 400 mA | 2.8006 W | 165.03 °C | −40.03 °C | 285.628571 mA |
Increasing load as shown causes overheating even though dropout and the entered current limit still pass.
Questions and troubleshooting
Why is maximum load below the current limit?
Thermal headroom can impose a tighter limit. The estimate also becomes zero when the dropout requirement is unmet.
Does a dropout warning predict output voltage?
No. It flags failure to meet the requested operating condition; it does not model the resulting output.
Does passing every check prove suitability?
No. Check capacitor stability, startup, transients, protection behaviour and derating in the selected device's datasheet.