Comprehensive interpretation of switching power supply testing: limit testing, reliability testing, white box testing, and conventional testing

1. Limit test
    1. Module output current limit test
    The module output current limit test is to test the current that the module can output after the output current limit point is released (the PFC overcurrent protection should also be released). The purpose of the test is to verify whether the current limit point design of the module is appropriate. Whether the device selection is appropriate. If the input current limit value of the module is too small, it indicates that the output current of the module is not enough; if the output current limit value of the module is designed to be too large, it indicates that the output current margin of the module is too high, and the cost of the module can be reduced.
    testing method:
    Release the output current limiting point of the module, and gradually increase the output current of the module by 5% of the rated output current. Keep each current value for 10 minutes until the module is damaged (or the output fuse is broken), and record the output current when the module is damaged The value 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 120%, no test is required).
    judgement standard:
    The current limit of the module must meet 110% to be qualified, and the test result shall be used as the basis for module design (reference data). Otherwise, it is unqualified.
    2. Static high voltage input
    test introduction:
    In static high voltage, the PFC circuit realizes overvoltage protection. This test is mainly to evaluate the reliability of the power module under static high voltage.
    testing method:
    A. Adjust the input voltage of the module to the static withstand voltage point according to the specifications, and run for 1 hour.
    B. Starting from the static withstand voltage point, increase the input voltage at a rate of 10V/10min until the module is damaged. The input voltage value when the module is damaged is the static limit input voltage of the module. Record the damage of the device and analyze the cause.
    judgement standard:
    In the above situation A, the power module is qualified without damage or other abnormal phenomena; otherwise, it is not qualified. Under Class B conditions, record the static input voltage of the module as a reference for the module's data. The test results under Class B conditions are only for reference, not as a criterion for judging whether it is qualified.
    3 Temperature rise limit test
    test introduction:
    The temperature rise limit test refers to the environmental temperature at which the module is damaged when the module's over-temperature protection fails. The purpose of the test is to investigate the environmental temperature the module can withstand, so as to provide a reference for the design of the module.
    testing method:
    Remove the temperature protection device of the module, and then place the module in a thermostat. The input voltage of the module is voltage and the output is power point. The temperature at the temperature protection relay of the module is monitored, starting from the ambient temperature of the module at 5oC/30min Gradually increase the ambient temperature at the speed until the module is damaged.
    Record content:
    When the module is damaged, the temperature rise of each key internal device is recorded, and the failure point is analyzed; the temperature extreme damage (operation time, temperature, damaged device, etc. details) is recorded for reference.
    judgement standard:
    The upper limit of the operating temperature defined in the specification, the power module is shielded from over-temperature protection, and the module will not be damaged if it is fully loaded for a long time.
    This test result can be used as a reference for model design. The criterion for judging is the distance between the temperature when the module is damaged and the temperature (or software protection point) at the protection of the module relay. If the difference between the two is negative, it means that the temperature relay is protected. The function (or software protection function) has no effect. If the difference between the two is 6-10oC, it means that the thermal margin of the module is too small. If the difference is greater than 40 degrees, it means that the margin is too large.
    4 EFT immunity test
    test introduction:
    Test the EFT immunity index that the power supply can withstand to confirm its margin. Test the product's ability to withstand the cumulative failure of the grid EFT generated by equipment such as high-frequency furnaces.
    testing method:
    A. Set the EFT anti-interference open circuit voltage to the specified level voltage +500V, and conduct an impact immunity test.
    B. With 500V as a step voltage level, repeat step A, each voltage level test is tested according to the standard EFT test method, and the test level voltage value of the deterioration and damage of the power supply performance is recorded (the test voltage is the voltage of the EFT immunity device ).
    C. Confirm the damaged part of the power supply and analyze the cause.
    judgement standard:
    The EFT limit value is greater than 5% of the specification, and it is qualified; otherwise, it is not qualified.
    5 Temperature shock strengthening test
    test introduction:
    Verify the high and low temperature impact limit that the product can withstand during storage and transportation.
    (1) Before the test, perform electrical and mechanical performance (appearance and internal structure) inspections in accordance with relevant specifications to ensure that the electrical and mechanical properties of the tested samples are normal before the temperature shock test.
    (2) The sample is not energized during the test, and no functional monitoring is performed.
    (3) After the test, check whether the mechanical properties (appearance and internal structure) are normal by visual inspection and other means. At the same time, the electrical performance should meet the requirements in accordance with the "Communication Power Module Basic Performance Test Specification".
    testing method:
    The method of temperature-enhanced impact test is shown in the figure below:
    HT: high temperature box temperature, 80 degrees
    LT low temperature box temperature, take -45 degrees
    Ncyc: cycle times, take 20T
    Dt: The residence time of the sample in the heat preservation section, take 45～60min
    Ct: Switching time between high and low temperature (determined by impact box, no need to choose)
    Attached table-temperature shock strengthening test conditions:
    Sample type High temperature box temperature HT Low temperature box temperature LT Holding time Dt Conversion time Ct Cycle number Ncyc
    Surface mount components made of board 130 -70 30min ≤5min 50T
    Common components made of board 100 -55 30min ≤5min 50T
    Whole machine 80 -45 45～65min ≤5min 20T
    Description:
    If there are both surface mount components and common components on the finished board, follow the requirements of common components. ?
    The heat preservation time of the whole machine can be selected between 45 and 65 minutes according to the size of the sample volume. Smaller volume is shorter, and larger volume is longer.
    Temperature shock test steps:
    (1) Before the test, check the mechanical properties (appearance and internal structure) and electrical properties of the tested samples to ensure that the mechanical properties and electrical properties of the samples are normal.
    (2) Arrange the sample reasonably in the temperature shock box, and leave enough space between the sample and the four walls of the temperature box to facilitate air circulation.
    (3) Select the temperature shock test conditions according to the above table.
    (4) Select the temperature shock test to start from high temperature, press the start button to start the temperature shock test.
    (5) The test will automatically stop after the set number of cycles.
    (6) After the test is over, take the sample out of the temperature shock box, and recover at room temperature until the sample temperature reaches a stable level.
    (7) Observe whether the sample after the test has mechanical damage (such as surface warpage, cracking, loose components, falling off, etc.) and check whether the electrical performance is abnormal.
    (8) If the above-mentioned mechanical damage occurs to the sample or the electrical performance index does not meet the relevant specifications, it is considered that the sample is also 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 there is no damage, the temperature impact level should be increased, and the general component made of the temperature impact test conditions in the above table or the surface mount component made of the board should be used to continue the test until the sample is damaged .
    judgement standard:
    The appearance, mechanical and electrical properties of the prototype are all normal and qualified; otherwise, it is not qualified.
    6 Low temperature step test
    test introduction:
    Verify the lower limit of the normal working temperature of the sample and the lower limit of the product damage temperature.
    (1) Before the test, check the mechanical properties (appearance and internal structure) and electrical properties of the tested sample to ensure that the mechanical and electrical properties of the sample are normal before the test.
    (2) During the test, power on for functional monitoring after holding for a period of time (about 15 minutes).
    (3) After the test, check whether the mechanical properties (appearance and internal structure) are normal through visual inspection and other means. At the same time, test the electrical performance according to the "Communication Power Module Basic Performance Test Specification" to meet the requirements.
    testing method:
    The low temperature stepping test method is shown in the figure below:
    Test conditions:
    According to the specification, select the working temperature, take -10 degrees as the starting temperature of the second step, and then reduce it by 10 degrees each time, and change to 5 degrees after finding the low temperature working limit.
    Low temperature test steps:
    (1) Before the test, check the mechanical properties (appearance and internal structure) and electrical properties of the tested sample to ensure that the mechanical and electrical properties of the sample are normal before the test.
    (2) Place the sample in the incubator without packaging and power supply, connect the input, output and measuring leads. There should be a proper distance between the test sample and the four walls of the incubator. Obvious impact.
    (3) Decrease the temperature box to the temperature setting value at a changing speed, and add a fan to balance the temperature during the cooling process.
    (4) After the temperature of the thermostat reaches the set temperature, the sample is kept at the set point for at least 15 minutes, and the internal temperature of the module is close to the same as the ambient temperature. The thermostat is set to wait mode at this stage.
    (5) Power on, start, perform basic performance tests in accordance with the specifications, and monitor the output voltage waveform, and fill in the observed phenomena in the record table in detail.
    (6) If the function is normal, proceed to step (7). If any of the monitored items exceeds the standard or is abnormal, it is deemed to have failed, and the failure temperature T and the failure phenomenon are recorded. Return the temperature to normal temperature for a long enough time for functional monitoring. If the function is found to return 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 and proceed to step (7); if the temperature is restored to normal temperature If the function is found to be unable to return to normal in a long enough time, it is considered that the tested sample has been damaged, find the damage limit of the sample, fill in the limit temperature in the test, and then stop the test and proceed to step (8).
    (7) Continue to cool down, repeat steps (3) ~ (7) until the damage limit of the sample is found or the low temperature limit of the incubator is reached.
    (8) Analyze the failure mode of the sample, find the weak link, and propose improvement measures.
    (9) Perform verification tests on the improved samples to ensure the effectiveness of the improvements.
    (10) Continue the test with the improved sample until:
    A. Reach the low temperature limit of the thermostat
    B. Abnormal failure occurs
    C. Compared with similar products, it is considered that the test can be terminated
    D. Continuing to improve will cost a lot of costs, and the gains outweigh the losses
    Note: (9) ~ (10) can be determined according to the actual situation.
    judgement standard:
    The appearance, mechanical and electrical properties of the prototype are all normal and qualified; otherwise, it is not qualified.
    7 High temperature step test
    test introduction:
    Verify the upper limit of the normal working temperature of the sample and the upper limit of the product damage temperature.
    1) Before the test, check the mechanical properties (appearance and internal structure) and electrical properties of the tested sample to ensure that the mechanical and electrical properties of the sample are normal before the test.
    (2) During the test, power on for functional monitoring after holding for a period of time (about 15 minutes).
    (3) After the test, check whether the mechanical properties (appearance and internal structure) are normal through visual inspection and other means. At the same time, test the electrical performance according to the "Communication Power Module Basic Performance Test Specification" to meet the requirements.
    testing method:
    The low temperature stepping test method is shown in the figure below:
    Test conditions:
    According to the specification, select the working temperature, take +10 degrees as the starting temperature of the second step, and then increase by 10 degrees each time, and change to 5 degrees after finding the high temperature working limit.
    Low temperature test steps:
    (1) Before the test, check the mechanical properties (appearance and internal structure) and electrical properties of the tested sample to ensure that the mechanical and electrical properties of the sample are normal before the test.
    (2) Place the sample in the incubator without packaging and power supply, connect the input, output and measuring leads. There should be a proper distance between the test sample and the four walls of the incubator. Obvious impact.
    (3) Raise the temperature box to the temperature setting value at a changing speed, and add a fan during the heating process to balance the temperature.
    (4) After the temperature of the thermostat reaches the set temperature, the sample is kept at the set point for at least 15 minutes, and the internal temperature of the module is close to the same as the ambient temperature. The thermostat is set to wait mode at this stage.
    (5) Power on, start, perform basic performance tests in accordance with the specifications, and monitor the output voltage waveform, and fill in the observed phenomena in the record table in detail.
    (6) If the function is normal, proceed to step (7). If any of the monitored items exceeds the standard or is abnormal, it is deemed to have failed, and the failure temperature T and the failure phenomenon are recorded. Return the temperature to normal temperature for a long enough time for functional monitoring. If the function is found to return 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 and proceed to step (7); if the temperature is restored After reaching room temperature for a long enough time, if it is found that the function cannot be restored to normal, it is considered that the sample under test has been damaged, find the damage limit of the sample, fill in the limit temperature in the test, and then stop the test and proceed to step (8).
    (7) Continue to heat up, 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) Analyze the failure mode of the sample, find the weak link, and propose improvement measures.
    (9) Perform verification tests on the improved samples to ensure the effectiveness of the improvements.
    (10) Continue the test with the improved sample until:
    A. Reach the high temperature limit of the thermostat
    B. Abnormal failure occurs
    C. Compared with similar products, it is considered that the test can be terminated
    D. Continuing to improve will cost a lot of costs, and the gains outweigh the losses
    Note: (9) ~ (10) can be determined according to the actual situation.
    judgement standard:
    The appearance, mechanical and electrical properties of the prototype are all normal and qualified; otherwise, it is not qualified.
    8 Insulation strength limit test
    test introduction:
    Test the insulation strength limit that the sample can withstand, and obtain the limit data.
    testing method:
    In regulation
On the basis of the insulation strength specified in the grid book, gradually increase by 10% (the leakage current requirements are consistent with the specification), and it is concluded that the internal insulation breakdown of the sample or the tester cannot continue to output high voltage. Each voltage level needs to be tested continuously for 60s.
     Record content:
     The limit value of the dielectric strength.
     If it is abnormal, record all abnormal phenomena.
     judgement standard:
     The limit value that the sample can bear is greater than 10% of the specification, and it is qualified; otherwise, it is not qualified.