LEPA B650 Power Supply Review

Primary Analysis

On this page we will take an in-depth look at the primary stage of the LEPA B650. For a better understanding, please read our “Anatomy of Switching Power Supplies” tutorial.

This power supply uses one GBU1506 rectifying bridge, which is attached to a heatsink connected to the heatsink of the active PFC transistors. This bridge supports up to 15 A at 100° C. So, in theory, you would be able to pull up to 1,725 W from a 115 V power grid. Assuming 80% efficiency, the bridge would allow this unit to deliver up to 1,380 W without burning itself out. Of course, we are only talking about this particular component. The real limit will depend on all the components combined in this power supply.

Figure 10: Rectifying bridge

The active PFC circuit uses two FCPF20N60 MOSFETs, each supporting up to 20 A at 25° C or 12.5 A at 100° C in continuous mode
(see the difference temperature makes) or 60 A at 25° C in pulse mode. These transistors typically present a 150 mΩ resistance when turned on, a characteristic called RDS(on). The lower the number the better, meaning that the transistor will waste less power, and the power supply will have a higher efficiency.

Figure 11: Active PFC transistors and diode

The output of the active PFC circuit is filtered by one 330 µF x 400 V Japanese electrolytic capacitor, from Rubycon, labeled at 85° C.

In the switching section, another two FCPF20N60 MOSFETs are employed using the traditional two-transistor forward configuration. The specifications for these transistors were already discussed above.

Figure 12: Switching transistors

The primary is managed by the famous CM6800 active PFC/PWM combo controller.

Figure 13: Active PFC/PWM combo controller

Let’s now take a look at the secondary of this power supply.