In the previous issue, we introduced how to solve common application problems of DC/DC power supplies . This time, we will focus on chassis switching power supplies. Chassis power supplies have a wide range of applications, and different application environments will have special requirements for the products. Therefore, some problems may occur during use, such as: abnormal startup output, large output ripple noise, isolation withstand voltage problems, or howling problems, etc. How can we troubleshoot and solve these possible power supply application problems? This article will mainly focus on chassis switching power supplies and analyze several common power supply startup faults.
The product has no output when powered on.
In daily use, complex application environments and component failures can cause power supplies to have no output after power-on, preventing downstream circuits from functioning properly. So what are the common causes of this?
● Input may be affected by lightning strikes, surges, or voltage spikes. Troubleshooting: Check for damage to components such as the fuse, rectifier bridge, and plug-in resistors at the product's input. Analyze the power-on waveform using a differential test. It is recommended to use the product in an environment that meets the EMS requirements specified in the technical manual. If use in harsher environments is necessary, an EMC filter and surge protection device should be added to the product's input.
● Input voltage far exceeds the product's maximum specification. Troubleshooting: Check the input fuse, plug-in resistors, large capacitors, and other components for integrity. Test the input voltage waveform to determine the problem. Recommendation: Adjust the input voltage, use a power supply with a suitable voltage, or replace the product with one that has a higher input voltage.
● Water droplets, solder dross, or other debris adhering to the product can cause internal short circuits. Troubleshooting: Check if the ambient humidity is within specifications; secondly, disassemble the product to check for debris on the surface mount and ensure the underside is clean. It is recommended to ensure the testing (use) environment is clean, and that the temperature and humidity are within specifications. If necessary, apply conformal coating to the product.
● Input cable breakage or poor contact at the connector port. Troubleshooting: Test the input voltage at the input terminal on the bottom of the product to ensure it is normal. It is recommended to replace the connector cable with a known good one, and ensure the connector port clips are securely fastened to prevent poor contact.
Long boot delay
In product applications, the main reasons for startup delays during normal connections are likely as follows:
● Low bus voltage results in low starting current and slow internal charging of the product. Troubleshooting: Use a multimeter to check the input bus voltage to confirm if it is within the product's rated range. Compare the input voltage range with the range indicated on the product label to check if it is within specifications. If using beyond specifications, we recommend using our products with a wider input voltage range.
No output upon startup / Abnormal output ( hiccups / jumps )
Everything is ready, but upon startup, there is no output or issues such as hiccups or fluctuating output. This could be due to external environmental interference or damage to external components. The main reasons are as follows:
● Excessive output load or short circuit / capacitive load exceeding specifications may cause overcurrent during startup. Troubleshooting: Disconnect the load and perform a no-load test to confirm normal output. Check for any oversized capacitive loads connected to the power supply and ensure there are no loads (such as motors) with high power requirements during startup connected to the power supply. Recommendations: Reduce the load and use the power supply within the range specified in the technical manual, or replace with a higher-power product. Products with stronger capacitive load capacity are recommended. It is also advisable to change the drive method of the downstream load and avoid direct drive by the power supply.
● Significant external interference during startup (When the power supply and high-power equipment are in the same system, the high-power equipment may lower the power supply line voltage during startup, affecting the power supply's startup. Simultaneously, the power supply may continuously interfere with the power supply line during operation, thus affecting its operation). Troubleshooting solution: Disconnect the large equipment and test the power supply module separately. It is recommended to isolate the power supply and the power supply network of the large equipment as much as possible to avoid simultaneous startup.
● Low ambient temperature causes electrolytic capacitors to lose capacitance, resulting in excessive ESR and poor startup. Troubleshooting solution: Confirm that the ambient temperature is within the product's operating temperature range, and confirm that the power supply has been appropriately dated under low-temperature load conditions. It is recommended to drate according to the derating curve under low-temperature conditions, and to select a power supply product with higher output power to meet low-temperature requirements.
● The external TVS diode for output protection is too small for the product's output voltage; the external TVS diode is reversed; or the capacitor is damaged. Troubleshooting: Remove the TVS diode and test the power supply's output voltage. The TVS diode should generally be 1.2 times the output voltage; however, it may not be necessary unless there are special requirements.
There are many types of power module failures. This article briefly explains some common chassis power supply startup problems mentioned above. Feel free to leave any further questions in the comments section !
