Let’s now take an in-depth look on the primary stage from Zalman ZM460-APS. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBU805 rectifying bridge on its primary, capable of delivering up to 8 A at 100º C. Zalman ZM360-APS uses a bridge with lower current limit (GBU606, which is a 6 A component), while SilverStone Strider ST50F uses a similar bridge with the same current limit but a higher voltage limit (GBU806). This bridge is more than adequate for a 460 W product: at 115 V this unit would be able to pull only up to 920 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 736 W without burning this component. Of course we are only talking about this component and the real limit will depend on all other components from the power supply. This bridge is attached to the same heatsink where the switching transistors are located.

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Figure 8: Rectifying bridge.

For the active PFC circuit Zalman ZM460-APS uses two SPA20N60C3 transistors, which one capable of delivering up to 20.7 A at 25º C or 13.1 A at 100º C in continuous mode (see the difference temperature makes) or up to 62.1 A in pulse mode. These are the same transistors used by SilverStone Strider ST50F, but Zalman ZM360-APS uses different transistors here, with lower current limits (STP14NK50ZFP: 14 A at 25º C, 7.6 A at 100º C and 48 A at 25º C in pulse mode).

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Figure 9: Active PFC transistors and diode.

The active PFC capacitor is from CapXon, a Taiwanese company, and rated at 85º C.

On the switching section two FQPF18N50V2 power MOSFETs are used on the traditional two-transistor forward configuration. Each transistor is capable of delivering up to 18 A at 25º C or 12.1 A at 100º C in continuous mode or up to 72 A at 25º C in pulse mode. These transistors are different from the ones used Zalman ZM360-APS and SilverStone Strider ST50F: ZM360APS uses two FQPF9N50C (9 A at 25º C, 5.4 A at 100º C and 36 A at 25º C in pulse mode) while SilverStone Strider ST50F uses two STF21NM50N (18 A at 25º, 11 A at 100º C and 72 A at 25º in pulse mode). As you can see while the transistors used on ZM460-APS and ST50F are different, they have similar specs, even though the ones used on ZM460-APS can deliver a little bit more current at 100º C, which is interesting.

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Figure 10: The two switching transistors.

The primary is controlled by the omnipresent CM6800 PWM/PFC controller combo.

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Figure 11: PWM/PFC controller.

Let’s now analyze the secondary section from ZM460-APS.