Microtest 6632S+ DC Bias Current Test System

The Microtest 6632S+ DC Bias Current Test System pairs the 6632S impedance analyzer with 6243H or 6243 DC bias sources for characterizing inductors, transformers, and magnetic components under realistic operating conditions. Each 6243H or 6243 source delivers 40 A, and up to 16 units run in parallel for a 640 A maximum (8 units and 320 A for the 6243). The system superimposes a controlled DC current onto the AC measurement signal, enabling measurement of inductance, impedance, and quality factor as a function of DC bias current, the fundamental data needed to evaluate inductor saturation behavior and select appropriate magnetic components for power converter designs.

Why DC Bias Testing Matters

Inductors used in switch-mode power supplies, DC-DC converters, and motor drives carry significant DC current during normal operation. The inductance of a magnetic component decreases as DC current increases, due to progressive saturation of the core material. An inductor rated at 10 uH at zero current may drop to 5 uH or less at its rated DC current. Without DC bias testing, designers and incoming inspection teams have no way to verify that an inductor will maintain sufficient inductance at its actual operating current, leading to converter instability, increased ripple, thermal runaway, and field failures.

Specifications

Feature	Specification
DC Bias Current, per source unit	0 to 40 A (programmable)
DC Bias Current, system maximum	640 A (16x 6243H) or 320 A (8x 6243)
Current Resolution	Fine step programmability
Compatible Instruments	Microtest 6630, 6632 series LCR/impedance analyzers
Measurement Parameters	L, Z, Q, ESR vs. DC bias
Sweep Mode	Automated DC current sweep with data capture
Protection	Over-current, over-temperature, DUT protection
Cooling	Active thermal management
Interface	Integrated control via host LCR meter
Connection	4-terminal with DC bias superposition

DC Bias Measurement Workflow

Step	Action	Data Generated
1	Set DC bias to 0 A	Baseline L, Z, Q at zero current
2	Increment DC bias in programmed steps	L, Z, Q at each bias point
3	Sweep to maximum rated current	Complete saturation curve
4	Analyze L vs. IDC curve	Saturation onset, knee current, rated current inductance
5	Compare against specification	Pass/fail against minimum inductance at rated current

The automated sweep mode steps through a programmed sequence of DC bias current values, measuring inductance and impedance at each point and generating the complete L-vs-IDC saturation curve. This curve reveals the saturation characteristics of the core material and air gap design: the current at which inductance begins to roll off (onset of saturation), the rate of inductance decrease (saturation slope), and the inductance remaining at the maximum rated current.

Application Scenarios

Power inductor design validation is the primary engineering application. Magnetics designers use L-vs-IDC curves to verify that prototype inductors meet the saturation specification before committing to production tooling. Comparing measured curves against simulation predictions validates the core material model and air gap design.

Incoming inspection of magnetic components ensures that production inductors from suppliers meet the saturation specification stated on the datasheet. Some inductor manufacturers specify inductance only at zero DC bias, while the actual application requires the inductor to maintain a minimum inductance at full rated current. DC bias testing catches components that meet the zero-bias specification but saturate prematurely at operating current.

Saturation current measurement determines the maximum DC current an inductor can carry before inductance drops below a specified threshold (typically 20% or 30% reduction from the zero-bias value). This is a critical selection parameter for power converter design, directly affecting converter stability and efficiency.

Production-line quality control for inductor and transformer manufacturers integrates DC bias testing into the production test sequence, verifying that every magnetic component leaving the line meets the saturation specification. Statistical process control of saturation current data enables early detection of core material variations, air gap dimensional drift, and winding process changes.

The 4-terminal connection maintains measurement accuracy by separating the DC bias current path from the AC measurement path, preventing DC-induced errors in the impedance measurement. Over-current and over-temperature protection circuits safeguard both the instrument and the device under test.

Watch the 6632S DC Bias Current Source System on YouTube

GSAS Micro Systems provides the Microtest 6632S DC Bias Current Source System with application consulting, fixture design, and integration services for Indian power electronics companies, magnetic component manufacturers, and component evaluation laboratories.