The graphics accelerator requires several voltages with low noise levels to operate - unstable power can cause any electronics to malfunction. To comply with the required parameters of the supply voltage on the video card, a DC-DC converter based on a PWM controller is used, which constantly monitors the state at the output of the converter and corrects it as necessary, and other circuitry solutions.
Video card systems can receive power both from the computer's power supply directly, and through the PCI-Express connector on the motherboard. As a rule, the most power-consuming components (video chip, video memory) are powered from one or more eight-pin 12V connectors, and the PWM controller, PCI-e bus controller and other low-power systems are powered directly from the PCI-e connector.
Depending on the current load on the video card, the amount of voltage on the power phases supplied to the GPU and video memory may vary within certain limits, ensuring the operation of energy-saving functions, reducing component heat and noise from cooling system fans during idle.
The principle of operation of converters for the video chip and video memory, which form the power phase circuit of the video card, is mainly as follows
- The PWM signal from the controller is fed to the gate driver of two n-type field effect transistors. The driver is necessary to accelerate the discharge of the parasitic capacitance formed by the electrodes of the field-effect transistor and preventing it from closing.
- Field-effect transistors form the upper and lower arms of the converter. Opening in turn, they then supply voltage to the next cascade, then put it on the ground. The operating time of the upper and lower arms is provided by the driver and is set by adjusting the width of the rectangular pulse that fills the period. If both transistors are turned on at the same time, a short circuit will occur.
- After a cascade of two field-effect transistors, the voltage is fed to an LC low-pass filter, consisting of a choke and a capacitor, which average the incoming pulses of switching on and off the power phase of the video card, producing a constant pulsating voltage at the output.
Thus, using the ability of a choke and a capacitor to accumulate and release a charge, it is possible to change the output voltage over a wide range - by switching them alternately with power plus or ground, the video card subsystems are provided with the necessary supply voltage depending on the current load.
In order to smooth out the output voltage ripples and provide a large flowing current, as well as reduce the heating of the elements of the power phase of the video card, they resort to parallelizing several identical converters connected to a common load, operating with a time shift (alternately) and adding an additional large-capacity tantalum capacitor. Each such converter is called the power phase of the video card.
Due to the fact that when the video card is operating in non-standard modes, for example, during overclocking or when it is not possible to maintain the temperature mode of operation due to the lack of proper maintenance of the cooling system, the current consumption of the graphics adapter may exceed the margin of safety of the components of one or more power phases, which is structurally incorporated by engineers video card, in which a breakdown of field-effect transistors occurs, as a result of which a short circuit occurs and, if the manufacturer decides to save on fuses, then the tracks on the board and all elements through which a huge short-circuit current flows can subsequently burn out.
Sometimes the performance of a video card can be partially preserved when one power phase fails if it did not provide voltage to a critical system, but such cases are extremely rare and it does not make much sense to consider them.
Modern video cards use specialized microcircuits that combine a driver and two powerful field-effect transistors in one chip - DrMOS, which literally stands for DRiver + MOSfet.
Repair of the power phase of the video card is necessary
- When you turn on the computer, there is no image on the monitor, while the coolers of the cooling system operate at maximum speed and make a lot of noise. At the same time, the video card itself, during a visual inspection, may look absolutely working.
- The printed circuit board of the video card has traces of thermal damage in the form of soot, burnt components, or a noticeable discoloration (darkening) of the electronic components and the board itself.
- There are "crashes" from programs that use the video card, and the operating system may display error messages.
Remember that when you try to independently repair the power phases of a video card, an avalanche-like failure of parts can occur: without the skills to diagnose malfunctions of complex electronic systems and in the absence of special measuring equipment, you can conditionally turn the need to replace one resistor into a long history of selection, search and replacement field effect transistors.