The power loop is an important part of the motherboard. Its function is to convert the current delivered by the host power supply to the voltage, and convert the voltage to the core voltage value that the CPU can accept, so that the CPU can work normally. , as well as shaping and filtering the current delivered by the host power supply, filtering out various clutter and interference signals to ensure the stable operation of the computer. The main part of the power loop is generally located near the motherboard CPU socket.
The power circuit can be divided into linear power supply mode and switching power supply mode according to its working principle.
Linear power supply method
This is the motherboard power supply method many years ago. It is realized by changing the conduction degree of the transistor. The transistor is equivalent to a variable resistor. Connected to the power supply circuit. Since the same current flows through the variable resistor and the load, a large amount of energy is consumed and the temperature rises, resulting in low voltage conversion efficiency. Especially in power supply circuits that require large currents, linear power supplies cannot be used. At present, this power supply method has long been eliminated.
Switching power supply mode
This is the currently widely used power supply mode. The PWM controller IC chip provides pulse width modulation and sends out pulse signals, causing the field effect transistors MOSFET1 and MOSFET2 to take turns. conduction. The chokes L0 and L1 are used as energy storage inductors and form an LC filter circuit with the connected capacitors.
The working principle is as follows: when the voltage VCORE across the load (such as the voltage required by the CPU) is to be reduced, through the switching action of the MOSFET field effect transistor, the external power supply charges the inductor and reaches the required voltage. rated voltage. When the voltage at both ends of the load increases, through the switching action of the MOSFET field effect transistor, the external power supply is disconnected, and the inductor releases the energy just charged. At this time, the inductor becomes a power source and continues to supply power to the load. As the energy stored in the inductor is consumed, the voltage across the load begins to gradually decrease, and the external power supply needs to be charged again through the switching action of the MOSFET field effect transistor. By analogy, in the process of continuous charging and discharging, a stable voltage is formed, so that the voltage at both ends of the load will never increase or decrease. This is the biggest advantage of the switching power supply. In addition, because the MOSFET field effect transistor works in the switching state, the internal resistance when it is turned on and the leakage current when it is turned off are both small, so its power consumption is very small, which avoids the consumption of the resistor part of the linear power supply connected in series in the circuit. A lot of energy issues. This is how the so-called "single-phase power loop" works.
Single-phase power supply can generally provide a maximum current of 25A, but today's commonly used CPUs have already exceeded this number. The power of the P4 processor can reach 70-80 watts, and the operating current can even reach 50A. Single-phase power supply cannot Provide enough reliable power, so the power supply circuit design of the motherboard now adopts a two-phase or even multi-phase design. (As shown in Figure 2) is a schematic diagram of a two-phase power supply. It is easy to understand. It is a parallel connection of two single-phase circuits, so it can provide double the current supply. In theory, it can be more than enough to meet the needs of the current CPU. But the above is just pure theory. In actual situations, many factors need to be added, such as the performance of switching components and the resistance of conductors, which are all factors that affect Vcore. In practical applications, there is an efficiency problem in the power supply part. The electric energy will not be converted 100%. Generally, the consumed electric energy is converted into heat and dissipated. Therefore, any common regulated power supply is always the hottest part of the electrical appliance. It should be noted that the higher the temperature, the lower the efficiency. In this way, if the conversion efficiency of the circuit is not very high, the circuit using two-phase power supply may not be able to meet the needs of the CPU, so three-phase or even more phase power supply circuits have appeared. However, this also complicates the motherboard wiring. If the wiring design is not very reasonable at this time, it will affect a series of problems such as the stability of high-frequency operation. Many mainstream motherboard products currently on the market use three-phase power supply circuits. Although they can supply sufficient power to the CPU, the stability of the motherboard in extreme situations is limited to a certain extent due to insufficient circuit design. If you want to solve This problem will inevitably require greater efforts in circuit design and wiring, and the cost will also rise.
The reason why the power supply circuit uses multi-phase power supply is to provide a more stable current. The pulse square wave signal sent from the control chip PWM is shaped into a DC-like current through the LC oscillation circuit. The high potential time of the wave is very short. The more phases there are, the closer the shaped quasi-DC current is to DC.
The power circuit plays a very important role in the performance of the computer and the stability of the work. It is an important performance parameter of the motherboard. When purchasing, you should choose products from mainstream manufacturers that are well-designed and use sufficient materials.