Power Supply de-rating

Power supply manufacturers are being pressured more than ever when it comes to size, power density and cost. As a result there are an increasing number of AC-DC power supplies released which rely on de-rating to improve their headline power ratings.

Information on such de-rating is often hard to find and at first glance, often not on short form data sheets. It can be found as a small piece of text at the end or bottom of a document and in some cases, long form data sheets must be obtained to properly identify the power supply needed to cater for an end system.

De-rating occurs when working with extreme temperatures or low line input voltages and applied to limit excessive component temperature rises and ensures componentry within end equipment doesn’t get too hot; Ultimately increasing reliability and life time.

Temperature de-rating

Most power supplies have a de-rating curve based on ambient temperature. This de-rating typically starts at ambient temperatures over 50°C and allows for temperature rises within the end equipment, whilst maintaining the full specified power rating of the power supply. When the ambient temperature rises to 70*C, the power supply performance is often 50%. It is also possible that a power supply needs to be de-rated if the ambient temperature drops below 0*C. There are still a small number of manufacturers who require this when designing products and this is based on start up.

In recent times, XP Power have started to design open frame power supplies that will work at full load up to 70*C. This limits any de-rating to above this temperature and means that the operating temperature range of the unit is increased for harsh environments. These products are classed as ultra high efficiency meaning waste hear is limited and critical components within an end system are kept cooler, increasing lifetime and reliability.

However, some manufacturers will state that a product operates in harsh environments and under extreme temperatures. This specmanship means that at first sight, their product appears lower cost and more power dense, however, when reading the de-rating curves the unit will only work to a fraction of its full rating. This means that a customer has to buy a bigger, more expensive unit to allow for de-rating.

XP Power offer a range of AC-DC product with market leading efficiency performance as well as very limited de-rating. These come in either Open Frame or Enclosed package styles. New to the XP range is the utra compact ECP130 series which offers 130W in a 2 X 3” footprint. As a result of very little heat loss through up to 95% efficiency, this product is able to perform up to 80*C.