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With the emergence and development of power modules, embedded engineers have reduced the time spent on detailed power design. At the same time, the variety of available modules has increased, raising the question: how should designers choose the appropriate DC/DC power module for an embedded application?
Context and Applications
Power electronics products continue to be developed and applied across many fields, and effective power design remains essential. Power design affects product performance and, in severe cases, whether a product functions correctly. Power design also tends to be specialized, with long debugging cycles and challenging fault diagnosis.
DC/DC power modules, characterized by small size, compact performance, ease of use, and relatively low total cost, are widely used in communication, networking, industrial control, rail, medical, and aerospace applications. Given the many models, differing specifications, and numerous manufacturers, selecting a cost-effective and suitable DC/DC module requires careful consideration.
Isolation vs Non-isolation
Whether a circuit needs isolation is a fundamental question for embedded system designers. Isolation serves two main purposes: safety isolation and noise isolation. Embedded hardware often involves multiple supply voltages, mixed-signal sections, and both high-speed and low-speed signals on the same PCB. Poor handling of those conditions can create interference, degrading performance or causing communication errors, system restarts, or failures.
Isolated DC/DC modules are therefore important in many embedded designs. Designers commonly use isolated modules to power different PCB regions, minimizing noise coupling and improving system stability. In systems that include industrial buses, designers must also consider surges, arcing, and lightning. In those cases, isolating the bus from core system circuits prevents ground loops and blocks adverse external effects from propagating into the core system, improving overall safety.
Performance and Cost Tradeoffs
Performance and cost often present a tradeoff. For DC/DC modules with the same input and output voltages, output power rating and operating temperature range are the main cost drivers.
Typical temperature grades are: commercial 0 to 70°C, industrial -40 to 85°C, automotive -40 to 105°C, and military -55 to 125°C. Different temperature grades impose different material and manufacturing requirements, which affects module cost. If package size is fixed and the module’s actual power usage is close to its rated power, the module’s specified temperature range must meet or slightly exceed the expected operating range.
If cost constraints lead to choosing a module with a narrower temperature range and the expected operating temperature approaches that limit, one mitigation is to derate the module. Select a module with a higher power rating or a larger package so the device runs cooler under the same load. In short, choose a wider temperature-range product with higher cost and potentially smaller package and fuller power utilization, or choose a lower-cost product with more conservative power margin and larger package. The right choice depends on the actual application requirements.
How Much Power Margin to Allocate
Design margin is intended to prevent unexpected conditions. While margin is not a direct indicator of quality, insufficient margin can create reliability risks, and excessive margin increases cost.
Embedded system loads vary: resistive, inductive, or capacitive; stable or highly variable; sometimes idle, sometimes full load, or experiencing sudden increases or drops. These variations complicate power rating selection. In general, load current is the key parameter determining required power. To improve stability and robustness, a minimum design margin of 20% is recommended. In other words, actual maximum power should not exceed 80% of the module’s rated power. Within this range, the module typically operates reliably and with acceptable temperature rise. Excessive margin wastes resources; insufficient margin harms temperature performance and long-term reliability.
For highly variable loads, ensure peak current stays within the module’s maximum capability, and increase margin according to the fluctuation frequency to enhance reliability.
Is Higher Isolation Voltage Always Better?
Not necessarily. Isolation voltage is an important specification for isolated DC/DC modules. Common ratings include 1000 VDC, 1500 VDC, 2000 VDC, 3000 VDC, and 6000 VDC. This rating indicates the maximum voltage the module can withstand between input and output for a specified period, typically 1 second.
Higher isolation ratings require more robust protection components and stricter manufacturing practices, which increases cost. The appropriate isolation voltage should be chosen based on the application. In many applications, very high isolation voltage is not required, but higher isolation can reduce leakage current and provide improved safety, reliability, and EMC performance.
Because embedded system cores are highly integrated and relatively sensitive, a common practical isolation level is 1500 VDC or higher for general applications. In specialized domains such as medical equipment, outdoor communication base stations, and high-voltage power systems, higher isolation requirements may apply.
Conclusion
With rapid technology development and shorter product development cycles, many embedded system designers recognize that selecting the correct DC/DC power module can save time on power design and debugging, improve overall system reliability, and shorten product development schedules.
