Secondary Analysis

This power supply has six Schottky rectifiers on its secondary, two for each positive voltage output (+12 V, +5 V and +3.3 V).

The +12 V output is produced by two STPS2045CT Schottky rectifiers connected in parallel. Since each one supports up to 20 A at 155º C we have a maximum theoretical current for the +12 V output of 40 A or 480 W. Of course the maximum current (and thus power) this line can really deliver will depend on other components, especially the transformer, the coil, the capacitors and the wire gauge used.

The +5 V output is produced by another two STPS2045CT Schottky rectifiers in parallel, supporting up to 20 A at 155º C each. So the maximum theoretical current the +5 V output can deliver is of 40 A or 200 W. Of course the maximum current (and thus power) this line can really deliver will depend on other components, especially the transformer, the coil, the capacitor and the wire gauge used, as we mentioned before.

The +3.3 V output is produced by two STPS20S100CT Schottky rectifiers in parallel, supporting up to 20 A at 150º C each. So the maximum theoretical current the +3.3 V output can deliver is of 40 A or 132 W. As mentioned the real power this line can deliver depends on other factors.

On this power supply the -12 V is regulated using a 7912 integrated circuit, which is great and explains why the -12 V output was so stable during our tests. Usually power supplies don’t use a voltage regulator circuit for this output and this is why it is usually far away from its nominal -12 V value.

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Figure 10: +3.3 V, +5 V and +12 V rectifiers.

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Figure 11: -12 V voltage regulator and +12 V, +5 V and +3.3 V rectifiers.

The thermal sensor is located on the secondary heatsink, as you can see on Figure 11. This sensor is used to control the fan speed according to the power supply internal temperature and to shut down the power supply in an overheating situation, if the power supply implements over temperature protection (OTP), which isn’t the case of this Cooler Master model.

This power supply uses a WT7527 monitoring integrated circuit, which is in charge of the power supply protections, like OCP (over current protection). OCP was really activated, as we will talk about later.

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Figure 12: Weltrend WT7527 monitoring integrated circuit.

On this power supply all electrolytic capacitors are rated at 85º C, using Thai capacitors from Elite on the voltage doubler circuit and Taiwanese capacitors from Ltec on the secondary.

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