This power supply uses one of the most unusual configurations we’ve ever seen on its secondary. We decided to draw a simplified schematics from the secondary so you can better understand the configuration used on this power supply. Read our Anatomy of Switching Power Supplies tutorial to compare the configuration used on this power supply with the configuration normally used. In the name of simplification we didn’t draw the controlling circuit of the MOSFET transistors and that is why we left their gates unconnected.

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Figure 11: Secondary from Rocketfish 700 W.

The +12 V output is produced by three Schottky rectifier packs. Two STPS30150CW are in charge of the direct rectification, while one STPS4045CW is in charge of the negative rectification. This is a very unusual design, as usually power supplies use the same number of diodes for the positive and for the negative rectification and also they are usually identical. Here we have four diodes for the positive rectification and two diodes for the negative rectification. Because of this asymmetrical it is not so easy to calculate the maximum theoretical power for the +12 V outputs.

The +5 V output is rectified thru an IRL7833 power MOSFET transistor. The +5 V and +3.3 V are interconnected using another two IRL7833 transistors. The +3.3 V output is rectified thru an SBL4040PT Schottky rectifier. Due to this hybrid configuration it is not so easy to calculate the maximum theoretical power for the +5 V and +3.3 V outputs.

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Figure 12: +12 V negative rectifier, transistor and +3.3 V rectifier.

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Figure 13: Transistors and +12 V rectifiers.

For the protection circuit instead of using a monitoring integrated circuit this power supply uses a discrete protection circuit, i.e. the manufacturer created their own protection circuit instead of using an off-the-shelf integrated circuit. For this circuit three quad-comparators integrated circuits (AS339) are used. These integrated circuits are located on a small printed circuit board located on the secondary. Because of the use of a customized circuit we couldn’t check exactly what protections this power supply really had (well, we could if we spent a lot of time analyzing this circuit). We could clearly see the over current protection (OCP) circuit, as we will explain on next page.

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Figure 14: Protection circuit.

All electrolytic capacitors are Taiwanese, Teapo, KSC, Fcon

The active PFC electrolytic capacitors are rated at 85º C (and manufactured by Teapo, a Taiwanese company), while the electrolytic capacitors from the secondary are rated at 105º C and coming from several vendors (Teapo, Fcon and KSC).