Constant-current LED driver planner

Assumptions to check

• The entered LED-driver-planner values represent the stated operating condition.
• This exact ideal relationship is evaluated in the declared lumped or first-pass model.
• A LED-driver-planner calculation is not a component qualification or safety approval.

What this LED-driver-planner calculation establishes

Calculate the current-sense resistor value and dissipation for a constant-current LED driver at its controller threshold. The useful result is the stated electrical quantity and the decision it supports, not an unstated claim about a finished product. This engine keeps the governing relationship visible so an input, unit, condition, or model boundary can be reviewed before a value becomes a component or layout choice.

Required sense resistance is the controller sense threshold divided by target current; sense-resistor power is current times sense threshold. Treat the number as a first-pass result for the declared operating point. When a source, load, temperature, frequency, waveform, component tolerance, or measurement condition changes, repeat the calculation at the relevant corner rather than assuming the nominal answer persists.

Worked decision context

A 100 mV sense threshold at 350 mA requires 0.2857 Ω and dissipates 35 mW in the sense resistor. That example verifies the equation and illustrates the scale of the result, but it does not select a part by itself. Compare the result with available values, ratings, tolerance bands, and the receiving circuit or physical environment before implementation.

Use the primary output to identify the binding constraint. If it leaves little margin, document which input dominates and use selected-part data, a higher-fidelity model, simulation, or measurement. This is especially important when a small numerical difference changes a thermal, timing, noise, or reliability decision.

Limits and validation handoff

LED compliance voltage, duty-cycle dimming, thermal derating, and the controller's regulation tolerance need a separate check beyond this sense-resistor sizing. The calculation does not silently include omitted parasitics, installation conditions, manufacturing variation, or product policy. Those conditions can be decisive even when the arithmetic is exact for the selected model.

Record inputs, units, model assumptions, and the intended decision with the result. Verify the leading risk against the selected component data sheet and a representative measurement when the circuit has consequential energy, high voltage, safety, compliance, or reliability requirements.

Common mistakes

• Treating the LED-driver-planner result as a guaranteed operating limit rather than a first-pass exact ideal relationship estimate.
• Mixing a data-sheet value measured under one condition with this LED-driver-planner calculation performed at another.
• Selecting a component before checking the boundary this calculation names: lED compliance voltage, duty-cycle dimming, thermal derating, and the controller's regulation tolerance need a separate check beyond this sense-resistor sizing.

Model limit and handoff

Keep the entered LED-driver-planner conditions with the calculation, then validate the binding limit using the selected component, physical implementation, and representative operating corner.

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