On this page we will take an in-depth look at the primary stage of 3R System iCEAGE IA450HP80. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one KBU806 rectifying bridge, which supports up to 8 A at 65º C if a heatsink is used, which is not the case. At 115 V this unit would be able to pull 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 itself. Of course we are only talking about this component and the real limit will depend on all other components from the power supply.

click to enlarge
Figure 9: Rectifying bridge.

Usually low-cost power supplies without PFC circuit are based on the obsolete half-bridge design, so it came as a surprise for us to see that iCEAGE IA450HP80 is based on a two-transistor forward design, which is the same design used by power supplies with active PFC. This is the first time we’ve seen a power supply without PFC using this topology.

In the switching section, two 2SK4108 power MOSFET transistors are used on the two-transistor forward configuration, as mentioned. Each transistor is capable of handling up to 20 A at 25º C in continuous mode, or up to 80 A at 25º C in pulse mode. Unfortunately the manufacturer does not provide the current limits at 100º C. These transistors present an RDS(on) of 210 mΩ. This number measures the resistance provided by the transistors when they are turned on; the lower this number, the better (higher efficiency).

click to enlarge
Figure 10: Switching transistors.

The switching transistors are controlled by a UC3843 PWM controller.

click to enlarge
Figure 11: PWM controller.

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