Logisys PS600A12 Power Supply Review

Primary Analysis

On this page we will take an in-depth look at the primary stage of the Logisys PS600A12. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

Instead of a using a ready-made rectifying bridge, the reviewed unit uses four discrete diodes. This is another evidence that we are dealing with a very low-end power supply. Four 1N5408 diodes are used, each one supporting up to 3 A at 75° C. Therefore, this unit would be able to pull up to 345 W from a 115 V power grid; assuming 80% efficiency, the diodes would allow this unit to deliver up to 276 W without burning themselves out. Of course we are only talking about these components and the real limit will depend on all other components from the power supply. Here you can tell that it is simply impossible for this power supply to be a 600 W unit.

Figure 10: Rectifying bridge

The electrolytic capacitors used in the voltage doubler circuit are Japanese, from Chemi-Con, and labeled at 105° C. But we wonder if they are not counterfeit parts.

The Logisys PS600A12 uses the obsolete half-bridge configuration, using two 2SD209L power NPN transistors, each one supporting up to 12 A at 25° C in continuous mode (unfortunately the manufacturer doesn’t say the limit at 100° C).

Figure 11: Switching transistors

The switching transistors are driven by a TL494 PWM controller, which is physically located in the secondary.

Figure 12: PWM controller

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