EP11 datasheet(37/46 Pages) POWERINT

37 / 46 page

22-Jan-01

EPR-00011 - 70 W Adapter

Page 37 of 46

Power Integrations Inc

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13 Appendix A - Thermal considerations:

The TOPSwitch-GX family significantly extends the power capability over the

TOPSwitch-II family of devices.

The higher power capability is a result of a lower

internal high voltage MOSFET RDS(ON) over that of any previous TOPSwitch-II. This lower

RDS(ON) enables compact high power adapters such as the EP11.

The output powers of higher power adapter supplies like EP11 are all thermally limited to

some degree. One of the important design considerations is often compact size which

together with efficiency limitations combine to limit the maximum continuous power of the

design. This adapter is no exception. The maximum continuous power is rated at 70

Watts in an enclosure at a 40

°C ambient temperature (see Figure 13). This rating is

very “packaging” dependent.

The power dissipated by the high voltage MOSFET within the TOP249Y is a significant

source of heat. Together with the heat generated in the transformer, output diodes, input

rectifier and filter, as well as the output filter must be managed to keep the maximum

component temperatures within limits.

Layout and heat sinking and the complete

package must be designed to manage the heat generated by the board components.

Adapters are generally completely enclosed external power sources that provide little or

no ventilation for the internal converter components. They are also generally small in

size which creates high power densities and necessitates very tight packaging of

components. The first and most fundamental performance element to optimise for a

successful high power adapter is its efficiency. Other key considerations include; heat

sink design, “hot spots”, and maximum component temperatures.

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