On this page we will take an in-depth look at the primary stage of Zalman ZM600-RS. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one D25XB60 rectifying bridge in its primary, which can deliver up to 25 A at 98º C if a heatsink is used, which is the case (without a heatsink the limit drops to 3.5 A at 25º C). At 115 V this unit would be able to pull up to 2,875 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 2,300 W without burning this component. That is what we call overspecification! Of course we are only talking about this component and the real limit will depend on all other components from the power supply.

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Figure 9: Rectifying bridge.

On the active PFC circuit two SPA20N60C3 power MOSFET transistors are used, each one capable of delivering up to 20.7 A at 25º C or 13.1 A at 100º C in continuous mode (note the difference temperature makes), or up to 62.1 A in pulse mode at 25º C. These transistors present a resistance of 190 mΩ when turned on, a characteristic called RDS(on). This number indicates the amount of power that is wasted, so the lower this number the better, as less power will be wasted thus increasing efficiency. These transistors are more powerful than the ones used on the 500 W model from Zalman RS series.

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Figure 10: Active PFC diode and transistors.

This power supply uses a Taiwanese capacitor from Teapo labeled at 85º C to filter the output from the active PFC circuit.

In the switching section, two STP14NK50ZFP power MOSFET transistors are used, each one capable of delivering up to 14 A at 25º C or 7.6 A at 100º C in continuous mode, or up to 48 A at 25º C in pulse mode, with an RDS(on) of 380 mΩ. These are the exact same transistors used on the 500 W model.

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Figure 11: Switching transistors.

The switching transistors are connected using a design called “LLC resonant,” also known as a series parallel resonant converter, being controlled by an L6598 integrated circuit. So far we’ve seen only a few power supplies using this kind of design, like Seasonic X-Series 650 W, Thermaltake Toughpower 800 W, SilverStone Nightjar 400 W and Zalman ZM500-RS.

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Figure 12: Resonant controller.

The active PFC circuit is controlled by a separated integrated circuit, an ICE1PCS02.

Now let’s take a look at the secondary of this power supply.