Designing in the power supply that you need!

Designing in a power supplyGlobal applications require a power supply that can deal with not only a universal AC input, typically 90-264 Vac, but also meet the customer’s lifetime expectations across all operating conditions.

It is quite common that the power supply manufacturer will specify a derating factor in the 90-115 Vac range. This is a decision that is made at the design phase and is influenced by the efficiency of the power supply at these input voltages, temperature of the components, lifetime and the cost to implement full load operation across the full input range.

So from an engineer’s point of view, when designing a PSU into their product, they must decide what is really needed. Are you making acceptable compromises in your design to meet the requirements functional, lifetime and cost balance.

A good example of a no compromise design is XP Power’s CCB200 series. The series has been designed with ultra high efficiency across the full input range. The product can deliver 200 Watts at temperatures up to +70 deg C and at input voltages as low as 90 Vac input in a 3 x 5" package. The efficiency at 90 Vac is still very high across the full load operating range. See below -

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What you often see offered is a product with a marketing specification that claims will meet the full operation, but looking into the detail frequently reveals derating for both input voltage range and operating temperature.

The graphs below are for a 3 x 5" 200W convection cooled product.

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Here we see at a typical ambient of +50 degC and at 90 Vac input the power supply can actually only deliver 120W, derating due to both temperature and input voltage. If used at full load and low line input in an ambient of +50 degC the lifetime would be severely limited.

If you truly only need 120W at +50 degC an alternative lower cost power supply could be specified to meet your overall cost/lifetime balance that would meet your real needs! However, as in most cases, if 200 Watts is required across the full input range and at up to +50 degC ambient, the datasheet should be read carefully to ensure the product suitably meets your requirements.

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