Isolated DC-DC Converters: High Density, 1.5kV to 6kV Isolation & Next-Gen Power Architecture

An unregulated isolated DC-DC converter has an output voltage that varies proportionally with input voltage changes and load variations (often varying by ±10% to ±15% depending on load). Unregulated converters offer higher efficiency, smaller footprints, lower cost, and high dielectric isolation—making them ideal for low-cost digital isolation or fixed-bus rail generation. A regulated isolated DC-DC converter incorporates internal feedback control loops (via optocouplers or auxiliary windings) to maintain tight output voltage accuracy (typically ±1% to ±2%) regardless of wide input voltage swings or 0%–100% load variations. Regulated converters are essential for precision analog sensors, microcontrollers, and wide-input battery systems.

Thermal derating is determined by evaluating the total power loss inside the converter ($P_{loss} = P_{out} \times (1 - \eta) / \eta$, where $\eta$ is efficiency), the ambient operating temperature inside the sealed case, and the converter's thermal resistance ($\theta_{JA}$ in °C/W). For example, if a 30W converter operates at 85% efficiency, it dissipates $5.29\text{W}$ as heat. In a still-air, enclosed environment without airflow, the internal ambient temperature rises quickly. Engineers must consult the datasheet's power-versus-temperature derating curve. If operating above the derating knee (e.g., above 70°C), output power must be derated by a set percentage (e.g., 2.5% per °C) or enhanced with thermal conductive potting, heat sinks, or mounting against an external metal chassis acting as a cold plate.

Clearance is the shortest distance through air between two conductive parts, while creepage is the shortest distance along the surface of an insulating material. Standard 1.5kVDC to 3kVDC industrial converters typically maintain clearance/creepage of 2.0mm to 3.0mm (suitable for IEC 62368-1 SELV circuits). Medical converters compliant with IEC 60601-1 3rd/4th Edition for Means of Patient Protection (2xMOPP) at 250VAC working voltage require a minimum clearance of 5.0mm and a creepage of 8.0mm, alongside an isolation test rating of 4000VAC or 5000VAC/6000VDC. Selecting pre-certified 2xMOPP Aimtec modules guarantees compliance with stringent medical device audits.

High-frequency switching topologies generate Common-Mode (CM) and Differential-Mode (DM) electromagnetic interference (EMI). Common-mode noise stems from parasitic capacitance ($C_{iso}$) between the primary and secondary transformer windings, allowing high-frequency current pulses to pass across the isolation barrier into system ground. To mitigate EMI: (1) Place a low-ESR ceramic capacitor filter network close to the input and output pins; (2) Install a differential inductor or pi-filter ($\pi$-filter) on the input line; (3) Add a Class-Y safety capacitor (e.g., 100pF to 1nF rated for the required isolation voltage) across the isolation barrier to provide a low-impedance return path for common-mode currents. Aimtec datasheets specify exact external filter schematics to achieve EN 55032 Class A or Class B compliance.

The Isolation Test Voltage (or Hi-Pot test voltage, such as 3000VDC or 1500VAC applied for 1 second or 1 minute) is a high-voltage stress factor applied during manufacturing testing to ensure the insulation system contains no pinholes, air gaps, or physical defects. It is a flash-test standard, not a continuous rating. The Continuous Working Voltage (e.g., 250VAC or 400VDC) is the maximum voltage difference the isolation barrier can safely withstand indefinitely across its multi-year operational lifetime without dielectric breakdown, partial discharge, or thermal degradation caused by corona effects.

Mean Time Between Failures (MTBF) is a statistical calculation expressing component reliability based on part count, thermal stress, and environment factor ($\pi_E$). An MTBF figure of 2,000,000 hours does not mean an individual converter will operate for 228 years; rather, it indicates that in a population of 2,000,000 units operating for one hour, one statistical failure is anticipated. Service Life (or operational lifetime) is determined by component wear-out mechanisms, primarily the drying of electrolytic fluid in output capacitors or thermal expansion stress in solder joints. Aimtec optimizes service life by adopting solid ceramic multilayer capacitors (MLCCs) and high-grade silicone encapsulation in isolated board-mount modules.

Yes. Series Operation: Outputs of identical isolated DC-DC converters can be connected in series to achieve higher voltage outputs (e.g., connecting two 15VDC outputs in series yields 30VDC). Reverse-biased Schottky diodes should be connected across each output to protect against voltage reversal during startup. Parallel Operation: Connecting outputs in parallel to increase current capacity requires care. Standard isolated converters without active current sharing may unbalanced load distribution, causing one converter to operate at current limit while the other under-delivers. Parallel connection is generally recommended using models featuring passive droop load sharing, OR-ing diodes, or specifically designated parallel-capable modules.

A standard 2:1 input range converter accommodates modest voltage fluctuations (e.g., 18-36VDC for 24V nominal). However, applications in railway rolling stock (EN 50155), mining equipment, and heavy industrial machinery experience severe voltage sags during motor start-up and high voltage surges during inductive load switching. A 4:1 input (e.g., 9-36VDC or 18-75VDC) or an ultra-wide 12:1 input (14-160VDC) allows a single converter model to operate seamlessly across standard 24V, 48V, 72V, and 110V supply rails, reducing SKU count, simplifying purchasing logistics, and enhancing system immunity against power line transients.