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MORE EFFICIENCY FOR AC POWER SUPPLY UNIT DESIGNS

2010-04-19  MPS

MP6901/2 from MONOLITHIC POWER SYSTEMS (MPS) to replace the secondary diode

It is becoming increasingly important to use energy sparingly in all areas of our lives. This places ever greater pressure on developers to make their power supply units more efficient so as to squeeze the last percentage points of efficiency out of their circuits.

High efficiency levels are not only necessitated by the ever more demanding statutory regulations, since thermal conditions and the available space on the printed circuit board also often mean that optimization is required.

Normally diodes are used in power supply units to rectify secondary voltages. Depending on the level of the voltage, Schottky or extremely fast diodes are used and these generate both switching and forward power losses. As the output current increases these losses drastically reduce the efficiency level of the entire power supply unit.

These Schottky diodes can be replaced with a circuit featuring the MP690x family from our supplier MPS resulting in the reduction of these losses to a minimum. The gain in efficiency of the entire circuit can amount to around 7% or more.

Figure 1 shows one way of reducing these losses by replacing the diode with a more efficient switch. Figures 2 and 3 show examples of actual solutions. The forward voltage through the MOSFET is then just 70 mV.

The MP6902 provides the added benefit that it detects low loads and reduces its own consumption to less than 0.3 mA.

Barrier voltages of up to 180 V may exist on the MOSFET with the maximum clock frequency being 400 kHz. The MP690x chip family can control both standard and also logic level FETs with extremely little delay (ton 50ns, toff 20ns).

Often these low losses on the secondary rectifier also make a heat sink superfluous. Not only does this reduce costs but also has a positive effect in terms of EMC. The installation on a heat sink together with the semi-conductors on the primary side generally results in interference due to capacitive coupling.

If you are also facing thermal problems, extreme efficiency requirements or space problems, this synchronous conversion could be the solution for you.

For further information about this product and advice on the complete solution, please contact us!

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Imp_1_2010_A14_MPS_Mehr Effizienz_MP690x application_Bild3.jpg
Fig. 1
Imp_1_2010_A14_MPS_Mehr Effizienz_MP6902 High-side application_Bild3.jpg
Fig. 3: High-Side

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