Addressing Partial Discharge in Miniature HV Converters

Conductors sit near insulation boundaries, and switching waveforms apply repeated voltage changes across compact internal structures. A converter might regulate its output during bench evaluation and still contain a localized insulation weakness that produces discharge activity. Addressing partial discharge in miniature high-voltage converters begins with understanding where electric fields concentrate and how manufacturing details affect those fields.

What Is Partial Discharge?

Partial discharge is a localized electrical event within or along an insulation system. The event bridges only part of the distance between conductors, so the converter continues operating after the first pulse. Repeated pulses erode solid insulation or damage an interface over time.

An air-filled cavity illustrates the process. Air has lower permittivity than many solid dielectrics, so the electric field across the cavity rises above the surrounding field. Once local stress exceeds the gas dielectric strength, a brief discharge sends a current pulse through the insulation network.

Internal void discharge differs from corona around an exposed conductor. Surface discharge follows an insulation boundary, while internal discharge develops inside a defect.

Miniature Packaging Increases Electrical Stress

Miniaturization reduces the physical distance available between nodes at different potentials. Narrow spacing increases electric field intensity even though the converter output remains within its specified range. Small packages place winding ends and multiplier stages near pins or grounded structures.

Field stress doesn’t distribute evenly through those spaces. Sharp metal edges or abrupt material transitions concentrate electric flux within a limited region. A nominal spacing value appears adequate on paper while one corner carries disproportionate stress.

Compact construction therefore depends on field control as much as basic clearance. Engineers must evaluate the three-dimensional structure because a side view obscures a short path near a lead bend.

Control Electric Field Concentration

Smooth conductor geometry reduces concentrated electrical stress. Rounded terminations spread field lines across a broad surface while pointed features compress them near the tip. Lead trimming and solder profiles therefore influence insulation behavior at high voltage.

Voltage grading provides another design tool. A resistor chain or distributed winding structure divides total voltage across several controlled steps. Each section then carries a defined share of the electrical stress.

Potential differences near package boundaries deserve separate analysis. A grounded shield may reduce radiated noise while increasing the field near an internal high-voltage node. Simulation reveals this tradeoff before tooling begins.

Select Insulation Under Stress

Dielectric strength provides only one part of material selection. Engineers must examine dielectric strength and permittivity as a combined electrical system. Thermal expansion and adhesion require equal review because moisture response affects long-term stability.

Permittivity differences influence field distribution at interfaces. A low-permittivity void inside a higher-permittivity resin receives elevated electrical stress. Strong adhesion reduces gaps between the encapsulant and component surfaces, although it won’t compensate for contamination or poor cure control.

Copper and ceramic expand at different rates during temperature cycling. With repeated movement, cracks will form and bonded surfaces will separate. It’s essential to select materials that support electrical insulation and mechanical continuity based on the specified temperature range.

Remove Voids During Encapsulation

Encapsulation protects compact HV circuits only when the process produces a continuous dielectric structure. Trapped air leaves regions with lower dielectric strength and distorted field distribution. Small bubbles near a conductor may initiate discharge below the level expected from bulk resin data.

Surface preparation controls the bond between resin and the assembly. Moisture, flux residue, dust, and oil create weak interfaces during curing. Cleaning procedures must match the substrate and leave no film that interferes with adhesion. Vacuum treatment removes dissolved gas and trapped air. Additionally, using controlled dispensing directs resin through narrow spaces without folding air into the material.

Manage Switching and Thermal Stress

A DC output doesn’t eliminate repetitive electrical stress inside the converter. Oscillator waveforms and multiplier stages expose internal insulation to changing voltage during every switching cycle. High edge rates intensify local fields near winding layers or component terminations.

Ripple and transient behavior deserve review at the actual operating point. A converter driving a capacitive load experiences startup conditions that differ from steady-state behavior. Load changes shift internal voltage distribution before the control loop settles.

Heat changes the insulation system through expansion and material aging. Local hot spots develop near switching elements even when case temperature remains acceptable. Thermal analysis must examine internal loss concentration because repeated gradients weaken interfaces under high electrical stress.

Verify Performance Through a Partial Discharge Test

A partial discharge test detects current pulses associated with localized insulation breakdown. IEC 60270:2025 covers charge-based measurements under AC voltages up to 500 Hz or DC. The standard defines measurement quantities and calibration practices across test circuits and methods for separating discharge from external interference.

A useful test raises voltage through controlled steps while the measurement system records apparent charge. Partial-discharge inception voltage marks the point where repeatable activity begins, while extinction voltage identifies the level where existing activity stops as voltage decreases.

Test fixtures must limit noise from the leads and connectors near the equipment. A noisy environment hides low-level activity or produces signals that resemble converter discharge. Baseline measurements and calibrated injection pulses establish whether the setup resolves the required charge level.

Test Across Operating Conditions

One room-temperature test won’t represent every service condition. Temperature changes material properties and mechanical dimensions across the encapsulated assembly. Reduced pressure lowers gas density, so airborne discharge may begin at a different voltage than it does near sea level.

Engineers must test representative input voltage and output settings across the load range. Polarity and startup behavior deserve separate evaluation. Each condition shifts electrical or thermal stress within the converter. A unit that passes at no load might show activity under a capacitive load because internal waveforms change during charging.

Production screening must follow the controlled setup used during qualification. Stable limits permit meaningful comparison across lots and process changes. Trend data exposes gradual movement before results cross the acceptance threshold.

Protect Compact HV Performance

Partial discharge in miniature HV converters demands coordinated control across design and manufacturing. For miniature HV DC-DC converters designed for your application, contact HVM Technology. We offer components designed for industrial and specialized electronic systems. Our support helps ensure dependable performance in demanding applications.