Custom Power Supply Design Challenges
Whenever a customer commissions the design of a custom power supply the engineer is faced with many requirements. Some of the factors to consider in determining requirements are listed below. Meeting the individual requirements is challenging. However, multiple requirements create opposite demands on the design. The greatest challenge is to make design decisions in order to best satisfy the need of the customer. In an ideal world, a power supply would be infinitely small, 100% efficient, last forever and cost nothing. In the real world compromises have to be made.
Working with an expert team is beneficial for the customer as these trade-offs can be clearly explained at the onset of the project. Trade-offs will have to be made according to the customer priorities. A customer requiring a power supply for an electrical shaver will emphasise low cost, whereas a customer requiring a power supply for a medical scanner will emphasise performance and safety of the patient.
A, non-exhaustive, list of factors for which requirements have to be determined is given here:
- Power density (physical size)
- Efficiency and Cooling
- Cost
- Reliability
- Ruggedness
- Output noise and ripple
- Electromagnetic compatibility
- Input voltage fluctuations
- Regulation and dynamic performance
- Component Sourcing and Procurement
Other factors to consider are also listed in Commissioning a Custom Power Supply. Challenges associated with setting requirements are described for a few of the above factors. Some emphasis is placed on the difficulty of placing requirements on contradictory factors.
Power Supply Design Challenges
Power Density
Real estate is at a premium for many customers, and high power density (the output power divided by power supply volume) is required. Since no power supply is 100% efficient, making a smaller one implies that heat generated by its operation will be concentrated in a smaller volume. This tends to increase the temperature of the components and have adverse effects on reliability and durability. Ingenuity is required to mitigate the problem. For example, in an air-cooled power supply, having the components in closer proximity restricts air flow. Great care has to be exercised to select and place the components within the enclosure such that air efficiently cools them down. Alternately, or complementarily, lower loss components can be used. Doing so, however, may have an effect on cost and on procurement. E.g.: some low loss materials for transformers and inductors are more expensive and have longer procurement time. Alternately power density may not be very critical for some industrial customers and design requirements priority may be shifted towards other factors.
Cooling
Cooling of components is always a major issue; air cooling has briefly been discussed in the previous paragraph. For most military products, direct air cooling is not an option. For some industrial customers, where the power supply operates in a highly polluted environment, direct air cooling of components may not be possible: a choice may have to be made between the use of air filters and the use of a cold plate. When the latter option is selected, components which generate radio frequency interference are tightly coupled to the cold plate. The cold plate, for safety reasons, is electrically connected to the remainder of the equipment. This allows for electrical noise to circulate outside of the power supply and makes Electromagnetic Compatibility (EMC) compliance more difficult.
Reliability
In general, high reliability implies running all components (transistors, diodes, transformers, inductors etc.) at a lower temperature. Increasing reliability often implies an increase in cost. For example, life of an electrolytic capacitor is exponentially related to its temperature and to the ripple current circulating through it. Thus if high reliability and long product life is desired, high-grade capacitors, larger size capacitors or a greater number of capacitors may be required. Depending on the solution this can increase cost and/or reduce power density.
Cost
The high performance of a product can be obtained through smart design decisions. These smart decisions can reduce the impact of the requirements on cost. However, this being said higher performance be it:
- Higher Efficiency,
- Lower Electromagnetic Emissions,
- Better Dynamic performance,
- Etc,
This usually results in a higher product cost. The design challenge thus resides both in finding the smart solutions and making the trade-offs between cost and performance.
Component Sourcing and Procurement
High-performance components may be difficult to procure. Also, selecting a component based on the latest fad can be enticing but detrimental to the overall project. When selecting components, the engineer must consider proven track record, availability, the probability of availability in the future and of course cost. Thus during the design process, they work with the procurement team to select components for the product. For example, a given high-performance capacitor may be attractive but difficult to procure and a greater number of lower performance capacitors may have to be used even if this decreases power density.
Overcoming Power Supply Design Challenges
The above examples barely scratch the surface of the task at hand when designing a power supply. Whenever commissioning the design of a custom power supply it is thus important to judiciously select the team you will be working with. We are expert power supply designers and can help with any power challenges you’re faced with.
Celab is a UK leader in power supply design and manufacturing. We provide complete custom power solutions for a wide range of environments, specialising in harsh environments such as land, air and sea. We’ve got a proven track record of creating high-quality rugged power supplies for military applications alongside industrial and manufacturing clients.
Contact us today to discuss your requirements or challenges, you can call on 01420 477011 or email at celab.info@murata.com