Topower TOP-1100P10 Power Supply Review

Secondary Analysis

As we mentioned, this power supply has two transformers instead of just one, as usual. They are controlled by the same circuit. On the secondary part, the first transformer (T3) is in charge of the +5 V and +12 V outputs and the second transformer (T4) is in charge of the +3.3 V and +12 V outputs.

The +12 V output uses a partial synchronous topology. The rectifying diode was replaced by a power MOSFET transistor (a.k.a. control transistor) while a freewheeling diode is still used instead of being replaced by another power MOSFET transistor (a.k.a. synchronous transistor) like on a true synchronous design.

Each transformer is connected to one IRFS3206 power MOSFET transistor, each one capable of handling up to 120 A at 25° C in continuous mode, or up to 840 A at 25° C in pulse mode. For the freewheeling diode three S60SC6MT Schottky rectifiers are used, each one able to handle up to 60 A at 110° C (30 A per internal diode).

The outputs of the two transistors are connected together; so on this power supply the use of two transformers has the same effect as if this unit were using only one bigger transformer.

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. In this case we will have to make our math with the freewheeling diode instead, which is made of six 30 A diodes connected in parallel. Just as an exercise, we can assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 257 A or 3,085 W for the +12 V output. As you can see the +12 V rectification is highly overspec’ed. The maximum current this line can really deliver will depend on other components, in particular the coil used.

The +5 V output is produced by two STPS60L45CW Schottky rectifiers, each one capable of handling up to 60 A (30 A per internal diode) at 135° C. 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 two 30 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 86 A or 429 W for the +5 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used.

The +3.3 V output is produced by one STPS60L30CW Schottky rectifier, which is capable of handling up to 60 A (30 A per internal diode) at 130° C. The maximum theoretical current the +3.3 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 30 A diode). 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 141 W for the +5 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used. It is interesti
ng to note since the +5 V and +3.3 V lines come from different transformers one output doesn’t limit the other as it usually happens.

On the secondary heatsink we also found the rectifier for the +5VSB (“standby power”) output, an SB1040F. This device can handle up to 10 A at 100° C (5 A per internal diode) supporting 150 A peak. This explains the higher current limit this power supply has for its +5VSB output (6 A) compared to other products (this is in fact the highest limit we’ve ever seen; most high-end power supplies can deliver up to 3 A or 3.5 A on the +5VSB output, with Corsair HX1000W being able to handle 4 A). Even though this power supply clearly uses an over dimensioned component here, we had trouble pulling 6 A from the +5VSB output, as you will explain in details later.

Figure 14: +5VSB diode, +12 V transistor, +12 V rectifiers and +5 V rectifier.

Figure 15: +5 V rectifier, +3.3 V rectifier, +12 V rectifier and +12 V transistor.

Instead of being monitored by a readily available monitoring integrated circuit this manufacturer decided to monitor the outputs using a discrete solution based on an LM339 integrated circuit located on a small printed circuit board. We should not forget that this power supply has a separated monitoring circuit for the ESA function, which is based on an 8051 microcontroller (C8051F320 to be more exact).

If you pay attention on Figures 14 and 15 you will see that this power supply has three temperature sensors. Two are connected to the ESA circuit while the third one is used to control the fan speed according to the power supply temperature.

The electrolytic capacitors from the secondary are from Hermei and Samson, two Taiwanese companies, and labeled at 105° C.