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Solving Power Supply Integration Issues
By Paul Kingsepp, Product Manager, SL Power Electronics Corp.
into equipment. Most designers search for and
D
choose a supply based solely on its published specifications, believing they have selected the right product for their application. Only after receiving the initial units for test and beginning the integration do poten- tial problems come to light. Most applications will allow rel-
atively simple integration of the power supply. Designers first deter- mine the basic needs of their equip- ment, i.e. the voltage needed to power the circuits and components, how much current the circuits will draw, the expected worst case ambi- ent temperature inside the equip- ment, the type of cooling, the size remaining to house the supply in the equipment, and any regulatory certi- fications. If most applications could get by with only knowing these par- ticular parameters, the designer’s job would be easy.
Regulating Surge Current If the equipment is to include
mechanical components (motors, fans, etc.), surge current may become an issue, as these types of compo- nents will draw an increased amount
esign engineers face many challenges when selecting and integrating power supplies
of current for a period of time when turned on. If the power supply was sized only for the components’
modes. It was requested that the cus- tomer provide the equipment and power supply together for testing.
what to look for. Conducted and radiated emis-
sions can also create challenges for the design engineer when integrating a power supply. Designers will select a unit that meets their desired level of emissions compliance, only to find that once introduced to the other com- ponents and circuits, the equipment is no longer in compliance. This may be caused by the interaction of the equip- ment’s circuits and the way the sup- ply is wired into the equipment. If the chosen power supply bare-
ly meets the required emissions com- pliance levels, then the chances of the system meeting these levels, without
Added margin will make up for some of the effects of system wiring, grounding, etc.
steady-state current, the additional surge current needed may not be available. In addition, there may be reverse polarity potential which the power supply could be subjected to, and if not considered, may cause reverse current flow and damage the supply. As an example, a customer had
issues with power supply failures, and initial analysis did not provide a clear reason for the exhibited failure
After analyzing the supply’s output during various phases of the equip- ment’s operation, it was found that when certain motors were turned off, a reverse potential was discovered on the power supply output which caused some of its components to fail. The addition of a few components alleviated the problem. This was not anticipated at the design stage, but something that may have been revealed earlier if the customer knew
If the chosen power supply barely meets the required emissions compliance
levels, then the chances of the system meeting these levels, without additional work by the designer, are slim.
additional work by the designer, are slim. Power supplies that meet the required emissions levels with “safe- ty” margins will allow easier integra- tion into the equipment.
Continued on page 60
December, 2015
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