Linear regulator and LDO thermal sizing
Dropout, quiescent-current loss, thermal current limit and an optional series pre-dropper.
Development preview. Check the assumptions below before relying on a result. Calculations run in your browser.
How it calculates
Assumptions
- Ground current is supplied from the input; verify your regulator topology and datasheet definition.
- Dropout and ground current are held constant. Current limit, thermal shutdown, reverse current and stability are device-specific.
- With a pre-dropper, reported current is the first continuous safe interval from zero load, capped by dropout; re-entrant thermal solutions are not advertised.
Worked example
These are the calculator's default inputs. Change any input above to recalculate.
Inputs
- Minimum input
- 7 V
- Maximum input
- 12 V
- Regulated output
- 5 V
- Load current
- 0.2 A
- Ground / quiescent current
- 0.005 A
- Required dropout at this load
- 1 V
- Series pre-dropper resistor
- 0 Ω
- Assembly thermal resistance
- 40 K/W
- Ambient temperature
- 40 °C
- Maximum junction temperature
- 125 °C
Results
- Worst-case junction temperature
- 98.4 °C
- Thermal-limited load current
- 0.295 A
- Minimum regulator input
- 7 V
- Minimum dropout margin
- 1 V
- Worst-case regulator power
- 1.46 W
- Pre-dropper power
- 0 W
- Maximum-input efficiency
- 40.6504 %
- Maximum resistor preserving dropout
- 4.87805 Ω