Feature: Power supplies


this results in immediate loss of the DC bus. Meanwhile, secondary-side faults, including short circuits or internal component failures, can propagate across the DC distribution network if not properly isolated. Voltage sags can cause a different type


of disturbance, reducing input energy and potentially compromising output stability. In parallel systems, uneven current sharing can overstress individual modules, accelerating thermal degradation whilst reducing overall system lifetime.


Designing better redundancy To reduce these failure modes, engineers oſten use redundant power architectures. In such systems the load is supported by several modules that are connected in parallel, typically based on the n+1 principle that ensures at least one additional module beyond normal operation requirements. Output decoupling is an important


aspect of redundant power system design. Traditional diode ORing, a technique used to connect two or more power sources to a single, common load, provides module isolation, but introduces forward voltage losses that reduce efficiency and increase thermal dissipation. In contrast, active output decoupling


using FETs provides lower-loss operation whilst maintaining effective fault isolation. In the event of a secondary-side short circuit, this prevents any disturbance on the DC bus if one module fails. Te remaining modules continue to supply the load, whilst the defective one signals its fault condition. Hot-plug capability


The semiconductor industry introduced the SEMI F47 standard, which defines the immunity requirements of production equipment against voltage sags


allows the module to be replaced without a system shutdown. Tese design approaches introduce


trade-offs that must be managed. Increasing redundancy improves fault tolerance but increases the cost, physical space requirements and system complexity. Similarly, while active current sharing and FET-based decoupling improve efficiency and performance, these architectures require additional control circuitry and design considerations. For engineers, achieving the ideal balance between reliability, efficiency and system complexity is therefore a key aspect of DC power system design.


Industrial processes that can’t tolerate power interruptions Te range of production processes that require fail-safe DC power is broad. In the chemical, glass and paper industries, certain processes can’t simply be restarted aſter an outage. In addition to downtime costs, the main risks include the loss of semi-finished products, frequently resulting in total loss of material and even plant damage. Te semiconductor industry is a


particularly demanding sector in terms of operational reliability. Te production of


large silicon ingots using the Czochralski process is followed by wafer processing that involves cycles that can last several weeks. Here, even a single interruption can cause substantial yield loss. To address such risks, the


semiconductor industry introduced the SEMI F47 standard, which defines the immunity requirements of production equipment against voltage sags. To support engineers working in this environment, power systems must be designed to preserve stable operation under these conditions. Achieving voltage sag immunity


becomes harder at lower mains voltages. While systems may meet SEMI F47 requirements at 230Vac (line-to-neutral), in Europe it is more difficult (with a common wide-range input of 85-265Vac operation at nominal 100/110Vac). One approach is to avoid operation between phase and neutral at low-line mains with 100/110Vac. Use of phase-to-phase connection instead results in an effective input of approximately 200Vac (line-to- line) and eases conformity to voltage sag immunity. For compliance with safety standards, this phase-to-phase operation requires devices with fuses in both conductors.


Figure 1: TDK-Lambda HFE3500 module www.electronicsworld.co.uk July/August 2026 29


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