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Experimental Characterization of SMD Inductors for Cryogenic Power Conversion at 4 K
Rami Rasheedi, Umeshkumar Patel, Jonathan Baldwin, Antonino Miceli, Inna Partin-Vaisband
TL;DR
Cryogenic power delivery can incur interconnect losses, but the behavior and converter-level trade-offs of inductors at low temperatures remain insufficiently understood. This paper characterizes commercial SMD power inductors at 4 K and evaluates their use in a simulated converter. It reports large DC-resistance reductions and improved converter efficiency, particularly at higher load currents.
Problem
Inductor behavior and the resulting efficiency trade-offs remain insufficiently understood for cryogenic power conversion, despite inductors being critical loss-dominant converter elements.
Source: §I · p. 2Method
The study experimentally characterizes commercial SMD power inductors at cryogenic temperatures and evaluates measured frequency-dependent impedance in converter-level simulations.
Source: §I · p. 2, §II · p. 4, §IV · p. 7Results
DC resistance falls 25×–58× at 4 K with 5–5.5% inductance degradation, while full-converter efficiency improves 3.0–5.2 percentage points at 1 A and up to 22.5 points at 3 A.
Source: §IV · p. 7Takeaways & Limitations
A representative simulated buck converter shows an efficiency advantage for cryogenic power conversion at higher current loads using commercial SMD power inductors.
Source: §IV · p. 7Converter-level evaluation is scoped to a representative single-phase buck converter simulated at 4 K.
Source: §IV · p. 7
Abstract
from arXiv · showhide
With the increasing complexity and scalability demands of cryogenic electronic systems, such as quantum computing platforms, conversion of power within the cryogenic environment has become a primary concern. Magnetic inductors are among the key components affecting converter performance, as their electrical and magnetic properties can change significantly at low temperatures. In this paper, five commercially available Vishay SMD power inductors are experimentally characterized down to 4 K: DC resistance is measured continuously during cooldown, while frequency-dependent AC inductance and resistance are measured up to 2 MHz at both room temperature and 4 K. The results show substantial DC resistance reductions of 25x-58x at 4 K, while the inductance degrades by only about 5-5.5%. Although cryogenic operation slightly increases the AC resistance (due to the intensified skin effect) and raises core losses, converter-level analysis shows an inductor-only efficiency improvement of approximately 5.3-6.9 percentage points at 1 A, and up to 22.8 points at 3 A. The measured frequency-dependent impedance of each inductor is imported into Cadence and a complete single-phase 24 V-to-1 V buck converter with GaN power devices is simulated at 1, 2, and 3 A at 4 K. The full-converter efficiency at 4 K is shown to improve by 3.0-5.2 percentage points at 1 A and by up to 22.5 points at 3 A for the AC-characterized devices. These findings indicate that commercially available off-the-shelf power inductors remain operationally viable under cryogenic conditions and can simultaneously increase inductor efficiency and reduce the overall power loss in cryogenic power conversion systems.
I. INTRODUCTION
Scaling cryogenic electronics makes power delivery increasingly challenging, while cryogenic power conversion remains difficult to assess because inductor properties and losses shift with temperature. This work addresses that uncertainty by characterizing commercial SMD power inductors and evaluating their cryogenic converter-level performance.
I. INTRODUCTION
- Long interconnects from room-temperature converters can introduce conduction losses, thermal loading, and signal degradation for 4 K electronics.As quantum processors scale, interconnect-related thermal load, Joule heating, and routing complexity are expected to become scalability bottlenecks.Source: §I · p. 1
- Cryogenic winding resistance falls, but reduced resistivity intensifies skin effect, making the AC-to-DC resistance ratio rise faster with frequency.The lower current penetration depth at low resistivity contributes to this frequency-dependent trade-off.Source: §I · p. 2
- Some ferrites lose over an order of permeability and show higher cryogenic core losses, while nanocrystalline and powder cores are generally more stable.The permeability and loss changes vary by core material and can alter achievable inductance and converter magnetic behavior.Source: §I · p. 2
- The net efficiency effect of cryogenic conversion remains uncertain because reduced delivery losses compete with changes in component performance, especially in inductors.Inductors are described as critical, loss-dominant elements, yet comparatively less explored than several cryogenic circuit components.Source: §I · pp. 1–2
- The study fills a gap between prior 4 K RF-inductor work and cryogenic power-conversion studies using bare or custom-wound cores.It characterizes commercial off-the-shelf SMD power inductors, including frequency-dependent AC loss, and evaluates them at converter level down to 4 K.Source: §I · p. 2
II. EXPERIMENTAL MEASUREMENTS
Five Vishay SMD power inductors were measured during cooldown and characterized for frequency-dependent AC behavior at room temperature and 4 K. At 4 K, their DC resistance fell substantially while inductance changed only slightly; the AC resistance reflected frequency-dependent winding and core losses.
Measurement setup
- Five Vishay SMD inductors were mounted on a custom four-wire board, cooled to 4 K, and measured for continuous Rdc and frequency-dependent AC inductance and resistance.AC measurements were made at room temperature and 4 K, up to 2 MHz.Source: §II · p. 3
DC resistance
- 25×–58× DC-resistance reductions at 4 K were observed across the five inductors, with Rdc settling below 30 K.The temperature-dependent measurements are shown in Fig. 6.Source: §II · p. 4, Figure 6 · p. 4
AC characterization
- Only two inductors received AC measurements up to 2 MHz, capturing the first several harmonics above their 360–670 kHz switching frequencies.The AC results are summarized in Fig. 7 and Table III.Source: §II · p. 4, Figure 7 · p. 4, Table III · p. 4
- At 4 K, inductance decreased by approximately 5–5.5%, while AC resistance rose more rapidly with frequency as skin effect intensified and core losses increased.Core losses become increasingly dominant at higher frequencies but remain relatively negligible at lower frequencies.Source: §II · p. 4
III. PERFORMANCE COMPARISON
At 4 K, reduced inductor DC loss outweighs the AC-loss trade-off, improving inductor-only efficiency across the evaluated loads. The analysis compares two inductors in a 24 V/1 V buck converter and checks thermal requirements.
III. PERFORMANCE COMPARISON
- The analysis evaluates a converter at load currents of 1 A, 2 A, and 3 A with 0.5 A peak-to-peak current ripple, focusing on inductor-related losses and efficiency under cryogenic operation.Source: §III · p. 5
- 6.9, 16.0, and 22.8 percentage-point gains for the IHLP2020BZER5R6M01 and 5.3, 14.2, and 20.2 points for the IHLP1212BZEV3R3MA1 at 1, 2, and 3 A, respectively.Fig. 9 presents the DC and AC loss breakdowns and efficiencies for both inductors at 300 K and 4 K; DC-loss reduction dominates in every case.Source: Figure 9 · p. 5, §III · p. 6
- 58.49× and 31.31× reductions in DC loss at 4 K for the IHLP2020BZER5R6M01 and IHLP1212BZEV3R3MA1, respectively.At 1 A, AC loss rises slightly at 4 K, but at 2 A and 3 A it falls; load-dependent switching frequency explains this crossover.Source: §III · p. 5
- Maintaining the inductor below approximately 20–30 K requires an effective thermal resistance to the 4 K stage of about 60–130 K/W, depending on operating point and temperature limit.The calculated loss at 4 K is approximately 0.2–0.25 W; actual thermal resistance depends on the package, board, interfaces, and stage coupling, and detailed electrothermal characterization is outside scope.Source: §III · p. 6
A. Transient Converter-Level Simulation
The time-domain simulations use measured inductor impedance and temperature-adjusted GaN devices to evaluate converter waveforms and efficiency. Cryogenic full-converter efficiency improves, with larger gains at higher load.
A. Transient Converter-Level Simulation
- The simulated 24 V-to-1 V buck converter uses measured frequency-dependent inductor impedance up to 2 MHz and cryogenically re-modeled GaN devices at 1, 2, and 3 A.The Touchstone one-port representation embeds measured frequency-dependent winding resistance and magnetic core loss, reproducing harmonic loading without a separate core-loss model.Source: A. Transient Converter-Level Simulation · p. 6
- At the representative 2 A load, both inductors regulate the output to 1 V with ripple within the 0.5 A target at both temperatures.The resulting full-converter efficiencies are compared across load current.Source: A. Transient Converter-Level Simulation · p. 6
- 3.0–5.2 percentage-point efficiency gains at 1 A widen to 19.1–22.5 points at 3 A under cryogenic operation.At 4 K, efficiency rises monotonically from 1 A to 3 A for both inductors; at 300 K, the IHLP2020BZER5R6M01 peaks near 2 A and then falls.Source: A. Transient Converter-Level Simulation · p. 7
IV. CONCLUSION
The paper experimentally characterizes commercial Vishay SMD inductors down to 4 K and simulates a representative GaN buck converter using their measured behavior. Reduced DC resistance dominates losses, and both inductor-only and full-converter efficiency improve.
IV. CONCLUSION
- At 4 K, DC resistance falls approximately 25×–58× while inductance degrades only 5–5.5%; reduced DC conduction loss dominates despite frequency-related AC resistance and core losses.The study experimentally characterizes commercial Vishay SMD power inductors with continuous DC-resistance measurements and frequency-dependent AC characterization.Source: §IV · p. 7
- 3.0–5.2 percentage-point full-converter efficiency gains at 1 A and up to 22.5 points at 3 A are reported for cryogenic operation.Inductor-only gains are 5.3–6.9 percentage points at 1 A and 20.2–22.8 points at 3 A.Source: §IV · p. 7
- The authors describe off-the-shelf power inductors as a practical, cost-effective option for cryogenic power delivery that can improve inductor efficiency and reduce long-interconnect conduction losses.They identify this as the first converter-level characterization of commercial off-the-shelf SMD power inductors down to 4 K for cryogenic DC–DC conversion, to their knowledge.Source: §IV · p. 7