SHARE

## Primary Analysis

On this page we will take an in-depth look at the primary stage of FSP300-60GHS. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBU605 rectifying bridge in its primary, which can deliver up to 6 A at 100° C. This component is clearly overspec’ed: at 115 V this unit would be able to pull up to 690 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 552 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.

Figure 9: Rectifying bridge.

On the active PFC circuit one FDPF18N50 power MOSFET transistors is used, capable of delivering up to 18 A at 25° C or 10.8 A at 100° C in continuous mode (note the difference temperature makes), or up to 72 A in pulse mode at 25° C. This transistor presents a resistance of 265 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. As you can see this power supply uses only one transistor instead of two, which is more common. This was done probably to reduce the size of the unit.

Figure 10: Active PFC diode and transistor.

This power supply uses a Teapo capacitor labeled at 105° C to filter the output from the active PFC circuit. It is always good to see power supplies using capacitors labeled at 105° C instead of 85° C here.

In the switching section, two FQPF9N50C power MOSFET transistors are used on the traditional two-transistor forward configuration. Each one is capable of delivering up to 9 A at 25° C or 5.4 A at 100° C in continuous mode (note the difference temperature makes), or up to 36 A in pulse mode at 25° C. These transistors present an RDS(on) of 800 mΩ (too high in our opinion).

Figure 11: Switching transistors.

The primary is controlled by a PFC/PWM combo controller from Champion Micro, but we couldn’t read the exact model.

Figure 12: PFC/PWM combo controller.

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

## Contents

Gabriel Torres is a Brazilian best-selling ICT expert, with 24 books published. He started his online career in 1996, when he launched Clube do Hardware, which is one of the oldest and largest websites about technology in Brazil. He created Hardware Secrets in 1999 to expand his knowledge outside his home country.