Let’s now take an in-depth look on the primary stage from Green Star 550 W (LW-6550SG). For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one T15XB80 rectifying bridge on its primary, capable of delivering up to 15 A at 100º C if a heatsink is used – which is not the case – but only 3.2 A at 25º C if a heatsink is not used. The difference is outrageous and Huntkey should have added a heatsink on this component. The current limit for this component is simply too low (3.2 A).  At 115 V this unit would be able to pull only up to 368 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver only up to 294 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 is the same component used on Huntkey Titan 650 W (Rocketfish 700 W), but at least this other product had a heatsink attached to it, which increased the current limit.

click to enlarge
Figure 10: Rectifying bridge.

LW-6550SG uses two 2SC3320 power NPN transistors on its switching section using the half-bridge design, supporting up to 15 A at 25º C (unfortunately the manufacturer from these transistors do not say how much they can deliver at higher temperatures). These are the same transistors used on Huntkey Titan 650 W (Rocketfish 700 W). These transistors are more “powerful” than the ones used on Green Star 400 W and 450 W. However the use of these transistors was not enough to prevent them from blowing up (we will talk about this is details later).

click to enlarge
Figure 11: One of the two switching transistors.

The two big electrolytic capacitors from the primary are from Teapo (a Taiwanese company) and rated at 85º C.