StarTech.com WattSmart 650 W Power Supply Review
Primary Analysis
Contents
We were very curious to check what components were chosen for the power section of this power supply and also how they were set together, i.e., the design used. We were willing to see if the components could really deliver the power announced by StarTech.com.
From all the specs provided on the databook of each component, we are more interested on the maximum continuous current parameter, given in ampères or amps for short. To find the maximum theoretical power capacity of the component in watts we need just to use the formula P = V x I, where P is power in watts, V is the voltage in volts and I is the current in ampères.
We also need to know under which temperature the component manufacturer measured the component maximum current (this piece of information is also found on the component databook). The higher the temperature, the lower current semiconductors can deliver. Currents given at temperatures lower than 50° C are no good, as temperatures below that don’t reflect the power supply real working conditions.
Keep in mind that this doesn’t mean that the power supply will deliver the maximum current rated for each component as the maximum power the power supply can deliver depends on other components used – like the transformer, coils, the PCB layout, the wire gauge and even the width of the printed circuit board traces – not only on the specs of the main components we are going to analyze.
For a better understanding of what we are talking here, please read our Anatomy of Switching Power Supplies tutorial.
This power supply uses a KBU10J rectifying bridge with a heatsink attached to it. This bridge can deliver up to 10 A at 75° C. This is more than adequate rating for a 650 W power supply. The reason why is that at 115 V this unit would be able to pull up to 1,150 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 920 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.
The manufacturer, however, scratched all other main components, making it almost impossible to identify them. This is the first time we’ve see such thing.
This power supply uses two power MOSFET transistors on its active PFC circuit and two other power MOSFET transistors on the switching section, which uses the traditional two-transistor forward configuration. From our experience we guess this power supply uses four 20N60C3 power MOSFET transistors, which are able to deliver up to 45 A at 25° C or 20 A at 110° C in continuous mode, or up to 300 A at 25° C in pulse mode. These transistors and the active PFC diode are located on the same heatsink.
Figure 10: Active PFC and switching transistors.
The integrated circuit in charge of controlling the active PFC and PWM circuits was scratched as well, but we believe that it is a CM6800, as this is the most popular integrated circuit for these functions.
