How to troubleshoot the switching power module failure

How to troubleshoot the switching power module failure?The power module has high reliability and has been widely used in communications, military, and electric power fields. During the application process, some faults may be encountered, which may cause the system to fail to start, and then burn the circuit. How to eliminate the power module failure?

Input voltage is too high

The input parameter for the power module is abnormal - the input voltage is too high. This is extremely light, which causes the system to fail to work properly and burns the circuit. So what is the cause of the input voltage being too high?

The output is suspended or unloaded; the output is too light, lighter than the 10% rated load; the input voltage is high or the interference voltage.

For this type of problem, you can adjust the load at the output or adjust the input voltage range as follows:

Ensure that the output is not less than 10% of the rated load. If there is no load in the actual circuit operation, connect a dummy load with a rated power of 10% at the output; replace a reasonable range of input voltage, when there is interference voltage Consider the TVS tube or Zener at the input.

Output voltage is too low

Abnormal output parameter for power module - output voltage is too low. This may cause the overall system to not work properly. For example, in a microcontroller system, the load suddenly increases, which will lower the power supply voltage of the microcontroller and cause a reset. And the power supply will work for a long time at low input voltage, and the life of the circuit will also be greatly damaged. Therefore, the problem of low output voltage can not be ignored, so the output voltage is too low is usually caused by those reasons?

The input voltage is low or the power is insufficient; the output line is too long or too thin, causing excessive line loss; the voltage drop of the anti-reverse diode at the input end is too large;

The input filter inductance is too large.

For this type of problem, it can be improved by adjusting the power supply or replacing the corresponding peripheral circuit, increasing the voltage or switching to a higher power input power supply. 

Adjust the wiring, increase the cross-sectional area of the wire or shorten the length of the wire, reduce the internal resistance; switch to a diode with a small conduction voltage drop; reduce the filter inductance value or reduce the internal resistance of the inductor.

 Output noise is too large

 Abnormal output parameter for power module - output ripple noise is too large. As we all know, noise is a key indicator to measure the strengths and weaknesses of power modules. In the application circuit, the design layout of the module will also affect the output noise. What is the cause of excessive output ripple noise?

The distance between the power module and the main circuit noise sensitive component is too close; the decoupling capacitor is not connected to the power input end of the main circuit noise sensitive component; the differential frequency interference occurs between the power modules of the single output in the multi-channel system; reasonable.

For this type of problem, it can be improved by isolating the module from the noise device or using a decoupling capacitor in the main circuit, as follows:

 Keep the power module as far as possible from the main circuit noise sensitive component or module and the main circuit noise sensitive component; the main circuit noise sensitive component (such as: A / D, D / A or MCU), the power input is connected to 0.1μF Coupling capacitor; use a multi-output power module instead of multiple single-output modules to eliminate the difference frequency interference; use a remote grounding to reduce the ground loop area.

 Poor power supply voltage

 Abnormal performance parameters for the power supply module - the power supply module has a low withstand voltage. Generally, the isolated power module has a withstand voltage of several thousand volts, but it may not be able to reach this indicator during application or testing. Which factors will greatly reduce its withstand voltage?

 The withstand voltage tester has a boot overshoot; the isolation voltage of the selected module is not enough; reflow soldering and hot air gun are used repeatedly during maintenance.

 For this type of problem, it can be improved through standard testing and specification use, as follows:

 During the withstand voltage test, the voltage is gradually increased; select the power module with high withstand voltage; when soldering the power module, select the appropriate temperature to avoid repeated soldering and damage the power module.