Light switch power supply undervoltage protection circuit repair - Power Circuit

MOS Power IC Full Range

LC03-3.3 SOP8 TVS Static Protection 3.3V

Probe Current Voltage Pin 420Ã—4450 Head Diameter 5.0 Over Current Current and Voltage Pin

As we all know, switching power supplies typically require a specific input voltage range. However, this range isnâ€™t always as broad as one might hope, since a reduction in the grid input voltage forces the power supply to draw more current from the mains circuit to sustain the output voltage. Lowering the input voltage increases the input current, leading to higher losses due to the internal resistance and line consumption of the mains. This results in a progressively decreasing supply voltage, creating a negative feedback loop that could ultimately cause the grid to collapse, posing significant safety risks. Some components within the switching power supply may overheat and suffer irreparable damage, causing catastrophic failures. To avoid such scenarios, undervoltage protection mechanisms are commonly integrated into switching power supplies. These circuits monitor the rectified voltage of the mains supply and shut down the system if the voltage falls below a safe threshold. While the circuitry for undervoltage protection is straightforward, its impact can be substantial. If this portion of the circuit malfunctions, the entire power supply may enter a protective shutdown mode. To further illustrate this concept, here are a few real-world repair cases Iâ€™ve encountered:

In one instance, a customer reported that their device would suddenly shut off without warning. After examining the power supply, I discovered that the undervoltage protection circuit had been triggered due to a loose connection on the input voltage line. Tightening the connection resolved the issue, and the device resumed normal operation. Another case involved a power adapter that consistently failed during high-load conditions. Upon inspection, it became apparent that the undervoltage protection circuit was being activated prematurely due to excessive ripple in the input voltage. Adding a filter capacitor at the input solved the problem, ensuring stable operation under all load conditions. These examples highlight the importance of properly designing and maintaining undervoltage protection circuits in switching power supplies. Neglecting these details can lead to costly repairs and potential safety hazards.
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