Thortech Thunderbolt 850 W Power Supply Review

Secondary Analysis

The Thortech Thunderbolt 850 W uses a DC-DC design in its secondary, meaning that this power supply is basically a +12 V unit, with the +5 V and +3.3 V outputs being generated by two smaller switch-mode power supplies connected to the main +12 V output. This design is proving to be the best solution to achieve high efficiency. Also, this unit uses a synchronous design for the +12 V rectification. This means that the rectifying diodes were replaced with transistors in order to increase efficiency.

The +12 V output uses eight AOT480 MOSFETs, each one capable of handling up to 180 A at 25° C or up to 134 A at 100° C in continuous mode, or up to 500 A at 25° C in pulse mode, with an RDS(on) of only 4.5 mΩ. Apparently, three are used for the direct rectification and five are used for the “freewheeling” part of the rectification.

Figure 14: The +12 V transistors

The +5 V and +3.3 V outputs are generated by two small power supplies available on small daughterboards attached to the +12 V rail. Each of these power supplies is comprised of four IPD060N03L MOSFETs (50 A at 100° C, 6 mΩ resistance) and one APW7073 PWM controller.

Figure 15: One of the DC-DC converters

This power supply uses a PS224 monitoring integrated circuit, which supports over voltage (OVP), under voltage (UVP) and over current (OCP) protections. The over current protection circuit available in this integrated circuit has four channels: one for +3.3 V, one for +5 V, and two for +12 V. This power supply, however, is sold as having four +12 V rails. We will talk more about the real rail configuration of this power supply in the next page.

Figure 16: Monitoring circuit

The electrolytic capacitors that filter the +5 V and +3.3 V rails are solid, while the capacitors that filter the +12 V rails are Japanese, from Chemi-Con.