Use this electronics calculation for a first-pass component, converter, signal, motor, or sensor estimate when the stated operating conditions and units match the device data.

Load power (W)

Required number input.

Holdup time (ms)

Required number input.

Input voltage (V)

Required number input.

Minimum voltage (V)

Required number input.

Compute the capacitance required to hold up a load from the input voltage down to a minimum voltage for a given time at constant power. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Required capacitance (µF)

The resulting required capacitance returned as a number.

• Power-supply ripple, hold-up, inrush, efficiency, and loss calculations depend on line range, load transient, switching mode, capacitor bias and ESR, rectifier conduction interval, control limits, temperature, and component tolerance. Safety, stability, EMI, and fault behavior require separate verification.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Check the result against the current datasheet and worst-case operating corners, then verify the circuit or measurement with simulation and bench testing where failure matters.

• Holdup Time

  Compute the holdup time of a bulk capacitor from the energy delivered between the input and minimum voltages at a constant load power.

• PSU Holdup Cap

  Compute the bulk capacitance needed to hold up a power supply output for a ride-through interval.

• Decoupling Cap Value

  Compute the decoupling capacitance C = I x dt / dV needed to supply a transient current for a droop time within an allowed droop voltage.