Light switch power supply undervoltage protection circuit repair - Power Circuit - Circuit Diagram

MOS power IC full range

LC03-3.3 SOP8 TVS Static Protection 3.3V

Probe current voltage pin 420x4450 head diameter 5.0 over current current and voltage pin

As most of us are aware, switching power supplies typically require a specific input voltage range. However, this range isn't necessarily as broad as one might think. When the grid input voltage drops, the power supply must draw more current from the main circuitry to maintain its output voltage. This reduction in input voltage leads to an increase in input current. With the internal resistance and line losses of the mains supply, the voltage becomes progressively weaker, creating a negative feedback loop that can ultimately lead to grid collapse, posing significant safety risks. Consequently, some components within the switching power supply may overheat and suffer irreparable damage, which can be catastrophic. To avoid such scenarios, it's common practice to implement under-voltage protection measures in switching power supplies. This involves designing an under-voltage protection circuit. Clearly, the sampling signal for this circuit comes directly from the rectified mains voltage. Although the circuit itself is relatively straightforward, its impact is substantial. If there's an issue with this portion of the circuit, the entire power supply system will shut down protectively. To reinforce this understanding, let me share a few practical repair examples I've encountered. One instance involved a power supply where the under-voltage protection circuit had malfunctioned due to a faulty resistor. Upon inspection, it was discovered that the resistor's value had drifted significantly over time, causing the circuit to misinterpret the input voltage. Replacing the resistor resolved the issue, and the power supply resumed normal operation. Another case involved a power supply where the under-voltage protection circuit was triggered unnecessarily, leading to frequent shutdowns. Further investigation revealed that the capacitors in the circuit had degraded, causing fluctuations in the sampling signal. By replacing the capacitors, the problem was successfully addressed, ensuring stable operation. These examples highlight the importance of proper under-voltage protection in switching power supplies. They also underscore the need for regular maintenance and testing of these circuits to prevent potential failures. In conclusion, while the concept of under-voltage protection may seem simple, its implementation plays a critical role in maintaining the safety and reliability of power supply systems.