Primary Analysis
Contents
On this page, we will take an in-depth look at the primary stage of the Sentey SDP850-SS. 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 the same heatsink as the primary transistors, but it is also attached to an individual heatsink. This bridge supports up to 15 A at 100° C if a heatsink is used, which is the case here. 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. Of course, we are only talking about this component. The real limit will depend on all the other components in this power supply.
Figure 10: Rectifying bridge
The active PFC circuit uses two IPP50R199CP MOSFETs, each one supporting up to 17 A at 25° C or 11 A at 100° C in continuous mode (note the difference temperature makes), or 40 A at 25° C in pulse mode. These transistors present a 199 mΩ maximum 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.
The active PFC circuit is controlled by an NCP1653A integrated circuit.
Figure 11: Active PFC controller
The output of the active PFC circuit is filtered by one 680 μF x 420 V electrolytic capacitor from CapXon, labeled at 85° C.
Figure 12: Capacitor
This power supply uses a resonant configuration with another two IPP50R199CP MOSFETs. The specifications for these transistors were already discussed above.
Figure 13: The two switching transistors, the active PFC diode, and one of the active PFC transistors
The switching transistors are controlled by a custom-made resonant controller called SF29601, which is physically located in the secondary. Since this is a custom integrated circuit, no datasheet is available for it.
Figure 14: Resonant controller
Let’s now take a look at the secondary of this power supply.
