Thortech Thunderbolt Plus 800 W Power Supply Review

Secondary Analysis

This power supply uses a synchronous design in its secondary, meaning that the Schottky rectifiers were replaced by MOSFET transistors in order to increase efficiency. On top of that, this unit uses a DC-DC design, meaning that this unit is basically a +12 V power supply, with the +5 V and +3.3 V outputs being generated by two small power supplies attached to the +12 V output.

The +12 V output is generated by four IXTH260N055T2 MOSFETs, each one capable of handling up to 260 A at 100° C in continuous mode or up to 780 A at 25° C in pulse mode, with an RDS(on) of only 3.3 mΩ. The leads of these transistors, however, are limited to 160 A. The +5 V and +3.3 V are produced from the +12 V output, but just as an exercise if all power from this unit was pulled exclusively from the +12 V rail, this unit would have a maximum theoretical current of 457 A or 5,486 W. That is what we call overspecification!

Figure 15: +12 V transistors

Usually power supplies that use DC-DC converters in the secondary to generate the +5 V and +3.3 V outputs have two separate printed circuit boards installed in the secondary, one for each output. In the Thortech Thunderbolt Plus 800 W, however, the manufacturer copied the idea used by Seasonic in their X-Series power supplies, installing these converters on the modular cabling printed circuit board.

Figure 16: The DC-DC converter

Figure 17: The DC-DC converter

Each output is managed by an APW7073 PWM controller, using two APM3109NU MOSFETs (50 A at 25° C or 35 A at 100° C in continuous mode, 120 A at 25° C or 80 A at 100° C in pulse mode, 7.5 mΩ resistance) and two APM3116NU MOSFETs (no datasheet is available).

The secondary is monitored by a PS232S integrated circuit. This chip supports over current protection (OCP), over voltage protection (OVP), under voltage protection (UVP) and over temperature protection (OTP). It is interesting to note that this chip supports six OCP channe
ls (four +12 V, one +5 V and one +3.3 V), but the manufacturer decided to configure this power supply with a single +12 V rail.

Figure 18: Monitoring circuit

On the solder side of the monitoring circuit printed circuit board we have an ATmega 88 microcontroller, in charge of the digital power meter.

Figure 19: Microcontroller for the power meter

All electrolytic capacitors used in this power supply are Japanese, from Chemi-Con, with some solid models also being used.