Let’s now take an in-depth look on the primary stage from Toughpower 1500 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.
This power supply uses two GBU1506 rectifying bridges connected in parallel on its primary, each one capable of delivering up to 15 A at 55º C (if a heatsink is used, which is the case), so the total capacity is of 30 A at 55º C.
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Figure 13: Rectifying bridges.
These bridges are shared among the two 750 W power supplies that exist inside Toughpower 1500 W. But all sections from now on are really separated. As we mentioned, usually power supplies using two transformers share at least the active PFC circuit. On Toughpower 1500 W everything is separated, including the active PFC circuit: separated switching transistors, separated PWM/PFC controlling circuit, separated transformers and separated outputs. So we are really talking about two independent power supplies here (well, not exactly, as they still share the rectifying bridges).
Each active PFC circuit uses two 20N60C3 power MOSFET transistors, the same used by several other power supplies we looked. Each one is capable of handling up to 300 A @ 25º C in pulse mode (which is the case) or up to 45 A @ 25º C or 20 A @ 110º C (see the difference temperature makes).
On each switching section this power supply uses two other 20N60C3 transistors, on the traditional two-transistor forward configuration. The specs for these transistors are published above.
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Figure 14: Active PFC diode, active PFC transistors and switching transistors.
Each primary is controlled by a CM6800 active PFC/PWM controller combo installed on a small printed circuit board.
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Figure 15: Active PFC/PWM controller combo.
