Power module limit test method

 

    1. Static high voltage input

 

　　Test instruction:

　　Under static high voltage, the PFC circuit implements overvoltage protection. This test is mainly to evaluate the reliability of the primary power module under static high voltage.

 

　　Test Methods:

　　A. Adjust the module input voltage to the maximum static withstand voltage point according to the specification and run for 1 hour.

　　B. Starting from the maximum static withstand voltage point, increase the input voltage at a rate of 10V/10min until the module is damaged. The input voltage value recorded when the module is damaged is the maximum static limit input voltage of the module. Record the damage of the device and analyze the cause.

 

　　judgement standard:

　　In the above case A, if the primary power module is not damaged or has other abnormal phenomena, it is qualified; otherwise, it is unqualified. Under Class B conditions, record the highest static input voltage of the module as a reference for the module data. The test results under Class B conditions are only used as a reference and not as a standard for judging whether it is qualified.

 

    2. Module output current limit test

　　The module output current limit test is to test the maximum current that the module can output after the output current limit point is released (the PFC overcurrent protection must also be released). The purpose of the test is to verify whether the module's current limit point design is appropriate and whether the module's device selection is appropriate. If the module's input current limit value is too small, it indicates that the module's output current is insufficient; if the module's output current limit value is designed to be too large, it indicates that the module's output current margin is too high and the module's cost can be reduced.

 

　　Test Methods:

　　Release the output current limit point of the module, gradually increase the output current of the module by 5% of the rated output current, and maintain each current value for 10 minutes until the module is damaged (or the output fuse is blown). The output current value recorded when the module is damaged is the output current limit value of the module. In order to prevent the module from being damaged by heat accumulation during the test, after each test point is tested, the module must be cooled to the cold state before the test. The current limit value of the test is 120% of the rated current of the module (that is, after exceeding 120%, no test is required).

 

　　judgement standard:

　　The current limit of the module must meet 110% to be qualified, and the test results are used as the basis for module design (reference data). Otherwise, it is unqualified.

 

　　3 Temperature rise limit test

　　Test instruction:

　　The temperature rise limit test refers to the maximum ambient temperature that causes the module to be damaged when the module over-temperature protection fails. The purpose of the test is to examine the maximum ambient temperature that the module can withstand, so as to provide a reference for the design of the module.

　　Test Methods:

　　Remove the module's temperature protection device, and then place the module in a temperature box. The module's input voltage is the lowest voltage, and the output is the maximum power point. Monitor the temperature at the module's temperature protection relay . Starting from the module's highest ambient temperature, gradually increase the ambient temperature at a rate of 5oC/30min until the module is damaged.

　　Record content:

　　When the module is damaged, record the temperature rise of each key component inside and analyze the fault point; record the damage at the temperature limit (operating time, temperature, damaged components and other details) as a reference.

　　judgement standard:

　　The upper limit of the operating temperature is defined in the specification, the power module is shielded from over-temperature protection, and the module is not damaged when working at full load for a long time. It is qualified; otherwise, it is unqualified.

　　The test result can be used as a reference for module design. The judgment standard is to see the distance between the highest temperature when the module is damaged and the temperature of the module relay protection point (or software protection point). If the difference between the two is negative, it means that the temperature relay protection function (or software protection function) is ineffective. If the difference between the two is 6 to 10 degrees Celsius, it means that the thermal margin of the module is too small. If the difference between the two is greater than 40 degrees, it means that the margin is too large.

 

　　4 EFT immunity test

　　Test instruction:

　　Test the highest EFT immunity index that the power supply can withstand to confirm its margin. Test the product's ability to resist cumulative failures caused by power grid EFT generated by equipment such as high-frequency furnaces.

　　Test Methods:

　　A. Set the EFT immunity open circuit voltage to the specified level voltage +500V and perform the impulse immunity test.

　　B. Repeat step A with 500V as the step voltage level. Perform each voltage level test according to the standard EFT test method and record the test level voltage value at which the power supply performance deteriorates and is damaged (the highest test voltage is the highest voltage of the EFT immunity equipment).

　　C. Confirm the damaged part of the power supply and analyze the cause.

　　judgement standard:

　　If the EFT limit value is greater than 5% of the requirement in the specification, it is qualified; otherwise, it is unqualified.

 

　　5. Temperature shock strengthening test

　　Test instruction:

　　Verify the high and low temperature impact limits that the product can withstand during storage and transportation.

　　(1) Before the test, the electrical and mechanical properties (appearance and internal structure) shall be checked in accordance with relevant specifications to ensure that the electrical and mechanical properties of the test sample are normal before the temperature shock test.

　　(2) During the test, the sample is not powered and no functional monitoring is performed.

　　(3) After the test, check whether the mechanical properties (appearance and internal structure) are normal by visual inspection or other means. At the same time, test the electrical performance according to the "Basic Performance Test Specification for Communication Power Modules" to ensure that it meets the requirements.

　　Test Methods:

　　The method of temperature enhanced impact test is shown in the figure below:

　　HT: High temperature box temperature, take 80 degrees

　　LT low temperature box temperature, take -45 degrees

　　Ncyc: number of cycles, take 20T

　　Dt: The residence time of the sample in the heat preservation section, 45 to 60 minutes

　　Ct: Switching time between high and low temperature (determined by the shock box, no need to select)

　　Appendix - Temperature shock strengthening test conditions:

　　Sample type High temperature box temperature HT Low temperature box temperature LT Insulation time Dt Conversion time Ct Cycle number Ncyc

　　Surface mount components made into boards 130 -70 30min ≤5min 50T

　　Ordinary components made into boards 100 -55 30min ≤5min 50T

　　Machine 80 -45 45～65min ≤5min 20T

　　illustrate:

　　If there are both surface mount components and ordinary components on the manufactured board, the requirements for ordinary components shall apply.

　　² The heat preservation time of the whole machine is selected between 45 and 65 minutes according to the size of the sample. The smaller the sample, the shorter it is, while the larger the sample, the longer it is.

　　Temperature shock test steps:

　　(1) Before the test, the mechanical properties (appearance and internal structure) and electrical properties of the test samples shall be checked to ensure that the mechanical and electrical properties of the samples are normal.

　　(2) Arrange the samples reasonably in the temperature shock chamber, and leave enough space between the samples and the walls of the temperature chamber to facilitate air circulation.

　　(3) Select the temperature shock test conditions according to the table above.

　　(4) Select the temperature shock test to start from high temperature and press the start button to start the temperature shock test.

　　(5) The test stops automatically after the set number of cycles.

　　(6) After the test, remove the sample from the temperature shock chamber and allow it to recover at room temperature until the sample temperature stabilizes.

　　(7) Observe the samples after the test for mechanical damage (such as surface warping, cracking, loose components, falling off, etc.) and check whether the electrical performance is abnormal.

　　(8) If the sample has the above-mentioned mechanical damage or the electrical performance indicators do not meet the relevant specifications, the sample is considered to be damaged and the test record form is filled in in detail.

　　(9) Analyze the weak links exposed by the test and propose improvement measures.

　　(10) Repair or improve the sample. If no damage occurs, increase the temperature shock level and continue the test with the ordinary component board level or the surface mount component board level in the temperature shock test conditions in the above table until the sample is damaged.

 

　　judgement standard:

　　The appearance, mechanical properties and electrical properties of the prototype are normal and qualified; otherwise, it is unqualified.

　　6 Low temperature step test

　　Test instruction:

　　Verify the lower limit of the sample's normal operating temperature and the lower limit of the product's damage temperature.

　　(1) Before the test, the mechanical properties (appearance and internal structure) and electrical properties of the test samples shall be checked to ensure that the mechanical properties and electrical properties of the samples are normal before the test.

　　(2) During the test, after keeping warm for a period of time (about 15 minutes), power is turned on for functional monitoring.

　　(3) After the test, check whether the mechanical properties (appearance and internal structure) are normal by visual inspection or other means. At the same time, test the electrical performance according to the "Basic Performance Test Specification for Communication Power Modules" to see if it meets the requirements.

　　Test Methods:

　　The low temperature step test method is shown in the figure below:

　　Test conditions:

　　According to the specification, select the lowest operating temperature, take -10 degrees as the starting temperature of the first step, then reduce it by 10 degrees each time, and change it to 5 degrees after finding the low temperature working limit.

　　Low temperature test steps:

　　(1) Before the test, the mechanical properties (appearance and internal structure) and electrical properties of the test samples shall be checked to ensure that the mechanical properties and electrical properties of the samples are normal before the test.

　　(2) Place the sample in the incubator without packaging and without power, and connect the input, output and measurement leads. There should be an appropriate distance between the test sample and the four walls of the incubator. The test sample should not have a significant impact on the inside of the incubator.

　　(3) Lower the temperature box to the set temperature at the maximum change rate, and add a fan during the cooling process to ensure the temperature reaches a balanced level.

　　(4) After the incubator temperature reaches the set temperature, the sample is kept warm at the set point for at least 15 minutes, and the internal temperature of the module is close to the ambient temperature. At this stage, the incubator is set to waiting mode.

　　(5) Power on, start the machine, perform basic performance tests according to the specifications, monitor the output voltage waveform, and fill in the observed phenomena in detail in the record sheet.

　　(6) If the function is normal, proceed to step (7). If any monitoring item exceeds the standard or is abnormal, it is considered to have failed, and the failure temperature T and failure phenomenon are recorded. The temperature is restored to normal for a long enough time to conduct functional monitoring. If the function is found to be restored to normal, it means that the sample is not damaged. T + 10 degrees is the low temperature working limit. Fill in the limit temperature in the test report and proceed to step (7); if the temperature is restored to normal for a long enough time, if the function cannot be restored to normal, it is considered that the test sample has been damaged. Find the sample damage limit, fill in the limit temperature in the test report, and stop the test and proceed to step (8).

　　(7) Continue cooling down and repeat steps (3) to (7) until the damage limit of the sample is found or the low temperature limit of the incubator is reached.

　　(8) Conduct failure mode analysis on samples, identify weak links, and propose improvement measures.

　　(9) The improved samples are subjected to verification tests to ensure the effectiveness of the improvements.

　　(10) Continue testing with the improved sample until:

　　A. Reach the low temperature limit of the incubator

　　B. Abnormal failure occurs

　　C. Comparison with similar products shows that the trial can be terminated

　　D. Continuing to improve will cost a lot, which is not worth the cost.

　　Note: (9) to (10) may be carried out based on actual conditions.

　　judgement standard:

　　The appearance, mechanical properties and electrical properties of the prototype are normal and qualified; otherwise, it is unqualified.

　　7 High temperature step test

　　Test instruction:

　　Verify the upper limit of normal operating temperature of the sample and the upper limit of product damage temperature.

　　1) Before the test, the mechanical properties (appearance and internal structure) and electrical properties of the test samples are checked to ensure that the mechanical and electrical properties of the samples are normal before the test.

　　(2) During the test, after keeping warm for a period of time (about 15 minutes), power is turned on for functional monitoring.

　　(3) After the test, check whether the mechanical properties (appearance and internal structure) are normal by visual inspection or other means. At the same time, test the electrical performance according to the "Basic Performance Test Specification for Communication Power Modules" to see if it meets the requirements.

　　Test Methods:

　　The low temperature step test method is shown in the figure below:

　　Test conditions:

　　According to the specification, select the highest operating temperature, take +10 degrees as the starting temperature of the first step, then increase by 10 degrees each time, and change it to 5 degrees after finding the high temperature working limit.

　　Low temperature test steps:

　　(1) Before the test, the mechanical properties (appearance and internal structure) and electrical properties of the test samples shall be checked to ensure that the mechanical properties and electrical properties of the samples are normal before the test.

　　(2) Place the sample in the incubator without packaging and without power, and connect the input, output and measurement leads. There should be an appropriate distance between the test sample and the four walls of the incubator. The test sample should not have a significant impact on the inside of the incubator.

　　(3) Raise the temperature box to the set temperature at the maximum change rate, and add a fan during the heating process to ensure that the temperature reaches a balanced level.

　　(4) After the incubator temperature reaches the set temperature, the sample is kept warm at the set point for at least 15 minutes, and the internal temperature of the module is close to the ambient temperature. At this stage, the incubator is set to waiting mode.

　　(5) Power on, start the machine, perform basic performance tests according to the specifications, monitor the output voltage waveform, and fill in the observed phenomena in detail in the record sheet.

　　(6) If the function is normal, proceed to step (7). If any of the monitoring items exceeds the standard or is abnormal, it is considered that failure has occurred, and the failure temperature T and failure phenomenon are recorded. The temperature is restored to normal for a long enough time to conduct functional monitoring. If the function is found to be restored to normal, it means that the sample is not damaged. T-10 degrees is the high temperature working limit. Fill in the limit temperature in the test report and proceed to step (7); if the temperature is restored to normal for a long enough time, if the function cannot be restored to normal, it is considered that the test sample has been damaged. Find the sample damage limit, fill in the limit temperature in the test report, and stop the test and proceed to step (8).

　　(7) Continue to increase the temperature and repeat steps (3) to (7) until the damage limit of the sample is found or the high temperature limit of the incubator is reached.

　　(8) Conduct failure mode analysis on samples, identify weak links, and propose improvement measures.

　　(9) The improved samples are subjected to verification tests to ensure the effectiveness of the improvements.

　　(10) Continue testing with the improved sample until:

　　A. Reach the high temperature limit of the incubator

　　B. Abnormal failure occurs

　　C. Comparison with similar products shows that the trial can be terminated

　　D. Continuing to improve will cost a lot, which is not worth the cost.

　　Note: (9) to (10) may be carried out based on actual conditions.

　　judgement standard:

　　The appearance, mechanical properties and electrical properties of the prototype are normal and qualified; otherwise, it is unqualified.

　　8 Dielectric strength limit test

　　Test instruction:

　　Test the insulation strength limit that the sample can withstand and obtain the limit data.

　　Test Methods:

　　Based on the insulation strength specified in the specification, gradually increase by 10% (the leakage current requirement is consistent with the specification), until the internal insulation of the sample is broken or the tester cannot continue to output high voltage. Each voltage level needs to be tested for 60 seconds.

　　Record content:

　　The limiting value of dielectric strength.

　　If there are any abnormalities, record them all.

　　judgement standard:

  　If the limit value that the sample can withstand is greater than 10% of the specification, it is qualified; otherwise, it is unqualified.