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PC Power Supply Circuit Explained-SMPS Tutorial
Dec
How should we troubleshoot a computer switching power supply
How should we troubleshoot a computer switching power supply, and where should we start when we’re faced with a faulty power supply? These are the topics you’ll learn in this tutorial.But before watching the video below to learn, you need to know that switching power supplies—no matter what type they are—have two main sections called the primary circuit and the secondary circuit.The primary circuit is the part where the mains AC voltage enters. In this section, the voltage is rectified, then smoothed by large capacitors, and after that it is distributed to the power transistors. In short, the primary circuit تحملs the highest voltage stress.That’s why most failures in switching power supplies usually happen in the primary circuit. And if a fault in the primary circuit is not identified and fixed in time, the secondary circuit will eventually start to fail as well.
We recommend that you first watch the video below and then continue reading the rest of the content.
Primary Circuit
A PC switching power supply (SMPS) is basically divided into two main sections: the primary side and the secondary side. Understanding the difference between these two parts makes troubleshooting a lot easier.The primary side is where the AC mains voltage enters the power supply. First, the input voltage is rectified and filtered using large electrolytic capacitors. After that, power MOSFETs switch this high DC voltage at a very high frequency using a PWM controller. This section handles high voltage and heavy electrical stress, so components like MOSFETs, startup resistors, PWM ICs, and primary capacitors are the most common failure points. Most SMPS problems usually start right here.
Secondary Circuit
The secondary side is completely isolated from the primary side by the transformer. Its job is to convert the high-frequency signal into usable low voltages such as 12V, 5V, and 3.3V. Fast rectifier diodes, output inductors, and capacitors are used to smooth and stabilize these voltages. Voltage regulation is done through a feedback circuit, usually with a TL431 and an optocoupler, which sends control information back to the primary side.When troubleshooting a faulty PC power supply, knowing whether the problem is on the primary or secondary side saves a lot of time. A failure in the primary side can prevent the supply from starting at all, while secondary-side faults often cause unstable voltages, shutdowns, or excessive ripple.
