AcBel Polytech iPower 660 Power Supply Review

Secondary Analysis

This power supply has four Schottky rectifiers on its secondary.

The +12 V output is produced by three STPS20S100CT Schottky rectifiers connected in parallel, each one supporting up to 20 A at 150° C (10 A per internal diode). The maximum theoretical current the +12 V line can deliver is given by the formula I / (1 – D), where D is the duty cycle used and I is the maximum current supported by the rectifying diode (which in this case is made by three 10 A diodes in parallel). Just as an exercise, we can assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 43 A or 514 W for the +12 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used. Usually good power supplies have this section overspec’ed, which isn’t the case with this power supply. We think the manufacturer should have given more headroom here (the maximum teoretical value is too low, probably indicating that this unit won’t be able to deliver its labeled power; let’s see what really happens later when we pull its full power). This situation is complicated by the fact that the +3.3 V output in generated from the +12 V output (more on this later).

The +5 V output is produced by one SBR30A40CT Schottky rectifier, which supports up to 30 A at 110° C (15 A per internal diode). The maximum theoretical current the +5 V line can deliver is given by the formula I / (1 – D), where D is the duty cycle used and I is the maximum current supported by the rectifying diode (which in this case is made by one 15 A diodes in parallel). Just as an exercise, we can assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 21 A or 107 W for the +5 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used. Here we think that the current/power limit is too low as well.

If you add both maximum theoretical values we calculated (514 W + 107 W) we have 621 W. Based on the components used on this power supply we don’t believe that it can deliver its labeled power. But let’s wait and see what happens when we put this unit on our load tester.

This power supply uses a voltage regulator integrated circuit for regulating the -12 V output (7912). This is a great option for producing this output, as it produces a more stable -12 V output.

Figure 11: +12 V rectifiers.

Figure 12: -12 V voltage regulator, +12 V rectifier and +5 V rectifier.

If you are following us you may have noticed that the +3.3 V rectifier is missing. This power supply uses an exotic configuration, where the +3.3 V output is achieved through a voltage regulator circuit connected to the +12 V output. Since the +3.3 V outputs are being generated using the +12 V rectifiers, the amount of current (and thus power) the +3.3 V and +12 V outputs can pull at the same time are limited by the maximum capacity of these rectifiers. This voltage regulator is located on a small printed circuit board, as you can see in Figure 13.

Figure 13: +3.3 V voltage regulator.

This power supply uses a WT7527 monitoring integrated circuit, which is in charge of the power supply protections, like OCP (over current protection). Unfortunately there is no datasheet for this component on the manufacturer’s website, so we couldn’t check what protections it really supports. Analyzing the printed circuit board from the reviewed power supply we could clearly see each +12 V virtual rail connected to this integrated circuit. OCP was really activated, as we will talk about later.

Figure 14: WT7527 monitoring integrated circuit.

The thermal sensor is attached to the secondary heatsink and you can see it in Figure 12. This sensor is used to control the fan speed according to the power supply internal temperature.

This power supply uses Chinese electrolytic capacitors rated at 85° C from Aishi on the active PFC circuit and Taiwanese capacitors from OST and Ltec rated at 105° C on the secondary.