iMicro PS-IM400WH Power Supply Review

Primary Analysis

On this page we will take an in-depth look at the primary stage of iMicro PS-IM400WH. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

Instead of using a ready-made rectifying bridge, the manufacturer decided to create the bridge using four discrete diodes. But instead of using four identical diodes, the manufacturer used two 1N5408 (3 A at 75° C) and two RL207 (2 A at 75° C) diodes. Because they are different, we have to consider the lower limit, which is 2 A, for our calculations. The 2 A diodes make this power supply to be able to pull only up to 230 W from a 115 V power grid. Assuming 80% efficiency, these diodes would allow this unit to deliver only up to 184 W. Here we can clearly see that this unit can’t be a 400 W power supply.

Figure 9: Rectifying bridge

In the switching section this power supply uses two 13007 power NPN transistors, connected using the obsolete half-bridge topology. Each one supports up to 8 A at 25° C (unfortunately the manufacturer doesn’t say the current limit at higher temperatures). These transistors are very popular among ultra low-end products.

Figure 10: Switching transistors

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

Figure 11: PWM controller

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