LDO Performance Calculator

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Evaluate LDO regulator power dissipation, efficiency, dropout margin, quiescent current loss, ripple rejection, regulation error, and current-limit margin in one engineering reference tool.

Input Parameters

Input Voltage Vin

Output Voltage Vout

Load Current

Quiescent Current

Dropout Voltage at Load

Input Ripple

mV peak-to-peak or RMS, keep same convention for output estimate.

PSRR

Current Limit

Results

Power Dissipation

Efficiency

Dropout Margin

Quiescent Power Loss

Estimated Output Ripple

Current Limit Margin

Design Note

Equations Used

Power Dissipation ≈ (Vin - Vout) × Iload + Vin × Iq

Efficiency ≈ Pout / Pin = (Vout × Iload) / (Vin × (Iload + Iq))

Dropout Margin = Vin - Vout - Vdropout

Output Ripple ≈ Input Ripple / 10^(PSRR/20)

Current Limit Margin = Ilimit - Iload

Frequently Asked Questions (FAQ)

Q1: What does this LDO performance calculator check?
It estimates LDO loss, efficiency, dropout headroom, ripple rejection, and current-limit margin.

Q2: Why is LDO efficiency low at high voltage drop?
An LDO dissipates the voltage difference between input and output as heat.

Q3: What is dropout margin?
It is the voltage headroom left after subtracting output voltage and dropout voltage from input voltage.

Q4: Does PSRR remove all input ripple?
No. PSRR depends on frequency, load current, headroom, capacitor network, and layout.

Q5: Why include quiescent current?
Iq can matter in low-power and battery applications and adds input power loss.

Q6: Can this replace thermal analysis?
No. Use power dissipation with package thermal resistance and board conditions for junction temperature.

Disclaimer: This calculator provides engineering estimates. LDO behavior depends on datasheet conditions, dropout curve, PSRR frequency, ESR stability, PCB layout, package thermal resistance, capacitor selection, and current-limit behavior.

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