How does IT equipment use AC power to provide power for its processing circuits? Will it also “shut down” 100 times per second (or more) when the polarity of the line voltage changes? It is obvious that there is a problem that the river equipment must solve here. In fact, all modern industrial equipment solves this problem by using switch mode power supplies (SMPS). 2SMPS first converts the AC voltage containing all non ideal state factors (voltage spikes, distortions, frequency changes, etc.) into a steady DC voltage. This process charges energy storage components (known as capacitors) located between the AC input and other power components. The capacitor is charged by the AC input when the sine wave reaches or approaches its peak (positive peak and negative peak) (with two pulses per AC cycle), and will discharge at any value required by the downstream IT processing circuit. Throughout the entire design lifecycle of a capacitor, it absorbs both normal AC pulses and abnormal voltage spikes. Therefore, unlike flickering light bulbs, I devices operate on stable DC rather than pulsating AC in urban power grids.
The discussion is far from over. Microelectronic circuits require very low DC voltages (3.3V, 5V, 12V, etc.), but the voltage through the capacitor mentioned earlier can reach up to 400V. SMPS also precisely converts this high voltage DC into low voltage DC output.
During this voltage reduction process, the SMPS performs another important function: providing current isolation. Current isolation is the physical isolation of a circuit to achieve two objectives. The primary purpose is to ensure safety and prevent electric shock. The second purpose is to prevent equipment damage or faults caused by common mode (ground) voltage or noise. SMPS smooths out the voltage transition between the peak values of AC input sine waves, and in the same way smooths out voltage changes during AC power supply anomalies and brief interruptions. This is a very important feature for IT equipment manufacturers, as they do not want their devices to malfunction solely due to very minor AC abnormalities. If the quality or performance of the power supply cannot withstand minor AC line abnormalities, I equipment manufacturers are risking their reputation. This is especially true for higher-level networks and computing devices, which typically come with higher quality power supplies built-in.
To demonstrate this tolerance, it is common to connect the computer power supply to a high-capacity load and then disconnect the AC input. Monitor the output of the power supply to determine how long the acceptable output voltage can continue to be provided without AC input. The displayed waveforms are the input voltage, input current, and DC output voltage of the power supply.
In summary, SMPS has the following advantages:
① They can accept wide range variations in input voltage and frequency without compromising performance.
② They have built-in current isolation devices between their AC input and DC output, so there is no need to use input common mode (zero line grounded) isolation measures.
③ They can accept significant input voltage distortion without reducing service life or reliability.
④ They have a built-in ‘withstand’ time that can tolerate brief power outages.