Quantifying Optical Rise Time and Current Transient Lag in High Current LED Drivers
Optical rise time lags current transients due to parasitic loop inductance, die junction capacitance, and non-linear quantum well carrier recombination kinetics.
Coaxial Current Viewing Resistor
Shunt Transducer
Non-inductive resistive geometry permits wideband current measurement in pulsed power electronics and fast-transient qualification test benches. Constructed with concentric tubular resistive elements and an inner potential pickup conductor, a coaxial current viewing resistor delivers flat frequency response from direct current into the gigahertz region. The coaxial construction cancels mutual magnetic flux coupling between the main current loop and the voltage sensing circuit.
This physical configuration yields precise voltage reproduction of sub-nanosecond current transients.
Metrological Performance
Skin effect in the cylindrical resistive foil establishes an intrinsic lower limit on high-frequency response time and phase distortion. High-bandwidth calibration certifies the coaxial current viewing resistor against transfer standards using impulse generators and fast-sampling digitizers. Resistance values typically range from several milliohms to a fraction of an ohm to balance signal voltage amplitude against thermal dissipation.
Production acceptance requires verification of pulse energy withstand ratings alongside temperature coefficient of resistance across the intended operating current range.
Signal Connection
Ground loop currents and external electromagnetic interference require double-shielded coaxial cabling between the transducer output and the recording oscilloscope. The compact outer shield of a coaxial current viewing resistor terminates directly into standard radio-frequency connectors to maintain continuous shielding integrity. Differential amplifiers or high-frequency isolation transformers eliminate common-mode ground voltages in high-side current measurement configurations.
Current Qualification
Sourcing specifications define maximum peak current, continuous average power dissipation, and maximum volt-second integral ratings for high-voltage discharge testing. Laboratories verify low inductance by applying sub-nanosecond rise-time step pulses and recording transient overshoot. The calibrated transducer establishes true current amplitude during laser diode driver characterization, semiconductor switching loss evaluation, and lightning surge simulation.