Switching LED driver
Buck or boost LED-string drive, sense resistance, dimming averages and output-ripple screening.
Development preview. Check the assumptions below before relying on a result. Calculations run in your browser.
How it calculates
Assumptions
- Analog dimming scales the sense reference; PWM dimming scales average output and resistor heat without changing the on-pulse operating point.
- LED current ripple applies a first-order current-divider response at the switching frequency to the power-stage ripple envelope. It is not an exact peak-to-peak waveform reconstruction.
- At very low analog duty, discontinuous switching and minimum on-time behavior may dominate.
Worked example
These are the calculator's default inputs. Change any input above to recalculate.
Inputs
- Topology
- buck
- Input voltage
- 24 V
- Each LED forward voltage
- 3 V
- Series LED count
- 5
- Full-scale LED current
- 0.35 A
- Sense reference voltage
- 0.1 V
- Analog dimming fraction
- 1
- PWM dimming duty
- 1
- Switching frequency
- 500000 Hz
- Inductance
- 0.0001 H
- Each LED differential resistance
- 0.5 Ω
- Effective output capacitance
- 0.000001 F
- Open-string OVP threshold
- 20 V
- OVP reference voltage
- 1.2 V
- OVP lower-divider resistor
- 10000 Ω
Results
- Current-sense resistor
- 0.285714 Ω
- Average LED current
- 0.35 A
- LED string voltage
- 15 V
- Sense resistor average power
- 0.035 W
- Ideal switch duty
- 0.629167
- Power-stage conduction
- CCM
- Inductor peak current
- 0.405996 A
- Switching-ripple LED-current estimate
- 0.012714 A