The parts of the Corsair AXi Digital Power Supply that makes them unique when compared to other desktop power supplies is the absence of a PFC/PWM controller IC (integrated circuit) on the power supply's primary side and a supervisor IC on the power supply's secondary side. Both of these parts have been replaced with DSP, which stands for "Digital Signal Processor".
AXi PSUs still use what's called a "resonant mode" topology like a lot of modern day super-efficient power supplies, but typically in other resonant mode PSUs a PWM controller IC changes the power supply's switching frequency based on an analog signal derived from the load measured at the transformer. This makes the power supply more efficient at a wider range of loads compared to other power supply topologies, but doing this alone can affect ripple and noise and voltage regulation.
The resonant mode controller, shown above, is just about the only IC you'll find in an AXi power supply that you may also see in other high end power supplies.
The supervisor IC is the heart of the power supply's safety functions. Functions like OCP (over current protection, which is protection from any one output drawing too much current), OPP (over-power protection, which prevents overloading), OVP (over-voltage protection, which measures if voltage goes too high), UVP (under-voltage protection), and SCP (short circuit protection). Temperatures are also measured within the power supply and this is reported to the IC's OTP (over-temperature protection). If any value programmed into the IC is exceeded, the IC is instructed to shut down the power supply.
Above is a supervisor IC found in a Corsair GS800 power supply.
In an effort to improve voltage regulation (drops in voltage as loads increase), the information concerning the power supply's output voltage is sent back to the PWM controller via an analog signal. This information moves relatively slow when compared to the ever-varying loads of your typical PC, so voltage regulation is still not as good as it can be.
Above is the PWM/PFC controller from a Corsair GS800 power supply.
AXi power supplies improve on this analog system by using the DSP. Like a supervisor IC, the DSP measures all of the pertinent information on the secondary side, as well as taking the same measurements on the primary side as your typical PFC/PWM controller IC. This information is also analyzed by the DSP's microprocessor and adjustments are made to the different components of the power supply in an effort to improve efficiency while maintaining very tight voltage regulation and minimizing ripple and noise. Because the signals are digital instead of analog and an inherently homogeneous DSP system is used to analyze the information as opposed to multiple ICs, adjustments can be made much faster than can be made with the typical set of ICs found in other desktop power supplies. And since the DSP is analyzing all of the same outputs (and then some!), the DSP still has the ability to act as a supervisor IC and shut down the power supply if any values exceed what is considered "safe" for the power supply or your computer.
Let's zoom in on some of the chips on this PCB. Shall we?
Above is a picture of the Freescale Digital Signal Controller found in the AXi series of power supplies. This chip handles what goes on on the primary side of the power supply. This guy is responsible for the PFC (power factor correction) control, the PMW (pulse width modulation) control, monitoring of the AC input's voltage, current and wattage and logical on/off control, like shutting down for inrush, brownouts, etc.
Above we see two more ICs found inside an AXi series power supply. The chip on the bottom is the main MCU, or "MCU I". The chip on the top is a USB MCU, or "MCU II". These guys handle what goes on on the secondary side of the power supply.
The MCU I does what we call "housekeeping". It has a lot of the same functions as a supervisor IC in an analog controlled PSU. Things like OCP, OPP, OVP, etc. are all monitored by this chip. This chip also handles the PMBus (power management bus) and thermal monitoring and fan control. The MCU I also monitors the power on (soft on/off) and power good signals coming from the motherboard. On top of all of this, the MCU I also monitors the DC output for voltage drop, ripple and noise and communicates back to the DSP to address any issues that may come up.
The MCU II is the chip that allows the user to turn on/off the single/multiple +12V rail capability of an AXi PSU via the Corsair Link software. The self test function is also controlled by this chip.
Since the DSP accumulates all of this information about the power supply, and does so in real time, we can deliver it to the end user via our Corsair Link software. Power supplies have attempted to deliver similar information about the power supply to the end user in the past; either via software or displayed on a 5.25" bay LCD. But since the information about the power supply in these older units was accumulated via the PFC/PWM controller and supervisor IC, the information had to be converted to a digital signal before being displayed. This adds a good deal of cost and prevents the information from being delivered as close to real time as possible.
Using Corsair Link, we can monitor everything from AC input voltage, output wattage... even the current being delivered to each graphics card's PCIe controller! Above you can see I've enabled OCP on each modular connector (essentially making the AXi a multiple +12V rail power supply) and turned all of the limits down to 20A.
We can also keep track of the temperature inside the power supply and how fast the fan is spinning:
All in all, AXi Digital Power Supplies are so much more than your average desktop PSU on so many levels. By utilizing a DSP, Corsair offers improved efficiency while maintaining stable voltage output and minimizing unwanted ripple and noise. And because all of this information is maintained in a digital format, output to the Corsair Link software interface is practically seamless!