How to test the switching power supply? On the method of passing the test of switching power supply

Date：2022-10-19 16:32:00Views：705

In many electronic and electrical circuits, switching power supply is a circuit with high failure rate. Once the switching power supply fails, it will lead to various other failures. Switching power supply has many advantages, such as high efficiency, small size, voltage rise and fall, negative pressure output, etc. However, in the actual use process, many designers ignored the test items of the switching power supply or did not understand the test items, resulting in many power supply products not meeting the specifications after being designed, or the function, performance and life are not up to the standard, so they need to redesign. This paper collects and sorts out some materials, hoping to be of great reference value to all readers.

1. Repeated short circuit test

Test description

Short circuit the module output under various input and output states. The module shall be able to realize protection or retraction. Short circuit repeatedly. After troubleshooting, the module shall be able to automatically resume normal operation.

test method

a. No load to short circuit: within the full range of input voltage, from no load to short circuit, the module shall be able to realize output current limiting or retraction normally. After the short circuit is eliminated, the module shall be able to resume normal operation. Let the module work repeatedly from no load to short circuit. The short circuit time is 1s, the release time is 1s, and the duration is 2 hours. After that, release the short circuit and judge whether the module can work normally.

b. Full load to short circuit: within the full range of input voltage, the module shall be able to realize output current limiting or retracting normally from full load to short circuit. After the short circuit is eliminated, the module shall be able to resume normal operation. Allow the module to be short circuited from full load for 2 hours. Then release the short circuit to judge whether the module can work normally.

c. Short circuit startup: short circuit the output of the module first, then energize it, and then energize it within the input voltage range of the module. The module should be able to achieve normal current limiting or retraction. After the short circuit fault is eliminated, the module should be able to resume normal operation. After repeating the above test for 10 times, let the short circuit release to judge whether the module can work normally.

Criteria

After the above tests, the power module can work normally when it is turned on; Check the power on case, the circuit board and other parts are free of abnormal phenomena (such as whether the input relay is stuck by electric shock during short circuit), and it is acceptable; Otherwise, it is unqualified.

2. Repeated on/off test

Test description

When the output of the power module is with the maximum load, the input voltage is 220v, respectively, (input overvoltage point - 5v) and (input undervoltage point+5v), the input is repeatedly switched, and the performance of the power module is tested repeatedly.

test method

a. The input voltage is 220v, the power module quickly carries the maximum load, uses the contactor to control the voltage input, closes for 15s, disconnects for 5s (or can be simulated with ac source), and runs continuously for 2 hours. The power module should be able to work normally;

b. The input voltage is overvoltage point - 5v, the power module carries the maximum load, the contactor is used to control the voltage input, the voltage is closed for 15s, the voltage is disconnected for 5s (or it can be simulated with ac source), and the power module can work normally after 2 hours of continuous operation;

c. The input voltage is - 5v at the undervoltage point. The power module carries the maximum load. The contactor is used to control the voltage input, which is closed for 15s and disconnected for 5s (or can be simulated with ac source). The power module shall be able to work normally after 2 hours of continuous operation.

Criteria

In the above tests, the power module works normally. After the test, the power module can work normally without obvious changes in performance, so it is qualified; Otherwise, it is unqualified.

3. Input low voltage point cycle test

Test description

The setting difference of the input undervoltage point protection of the primary power supply module often occurs in the following situations: the input voltage is low, the undervoltage point close to the primary power supply module is turned off, the undervoltage occurs when the primary power supply module is loaded, and after the switch off, due to the internal resistance of the power supply, the voltage will rise after the load is removed, which may cause the primary power supply module to be in the state of repeated development at low voltage.

test method

The power module operates with full load, the input voltage changes slowly from (input undervoltage point - 3v) to (input undervoltage point+3v), the time is set as 5-8 minutes, and the power module operates repeatedly. The power module should be able to work normally and stably, with continuous operation for at least 0.5 hours, and there is no obvious change in the performance of the power module.

Criteria

The primary power supply module operates normally and continuously, and there is no obvious change in performance after at least 0.5 hour, so it is qualified; Otherwise, it is unqualified.

4. Input transient high voltage test

Test description

The average value circuit is used for over-voltage and undervoltage protection in the pfc circuit. Therefore, when the transient high voltage is input, the pfc circuit may achieve protection quickly, resulting in damage. Test the stable operation capability of the primary power module under the transient condition to evaluate the reliability.

test method

a. For rated voltage input, use a dual trace oscilloscope to test the input voltage waveform and overvoltage protection signal. The input voltage jumps from 5v at the power limiting point to 300v. Read the cycle number n of 300v before overvoltage protection from the oscilloscope as the basis for the following tests.

b. Rated input voltage, the power module operates with full load, superimposes 300v voltage jump on the input, the superimposed cycle number is (n-1), the superimposed frequency is once/30s, and the total operation time is 3 hours.

Criteria

The primary power supply module can operate stably under the above conditions without damage or other abnormal phenomena, acceptable; Otherwise, it is unqualified.

5. Input voltage drop and output dynamic load

Test description

During the actual use of the primary module, when the input voltage drops, the limit condition of sudden load on the power module may occur. At this time, the power devices and magnetic components work in the maximum transient current state. The test can verify the rationality of the control timing, current limiting protection and other circuit and software design.

test method

a. Adjust the input voltage to jump between the undervoltage point+5v (duration: 5s) and overvoltage point - 5v (duration: 5s), and adjust the output voltage to jump between the maximum load (maximum rated capacity, duration: 500ms) and no-load (duration: 500ms) for 1 hour;

b. Adjust the input voltage to jump between the undervoltage point+5v (duration: 5s) and overvoltage point - 5v (duration: 5s), and adjust the output voltage to jump between the maximum load (maximum rated capacity, duration: 1s) and no-load (duration: 500ms) for 1 hour.

Criteria

Under the above conditions, it shall be able to operate stably without damage or other abnormal phenomena, and it is qualified; Otherwise, it is unqualified. In case of damage, record the fault to provide the basis for analyzing the cause of damage.

6. High voltage no-load and low voltage current limiting operation test

Test description

High voltage no-load operation is to test the loss of the module, especially the module with soft switch technology. In the no-load condition, the soft switch becomes a hard switch, and the loss of the module increases accordingly. Low voltage full load operation is to test the loss of the module at the maximum input current. Normally, the module has the lowest efficiency at the low voltage input and full load output, and the heating of the module is the most serious.

test method

a. Adjust the input voltage of the module to - 3v of the input overvoltage protection point, and the output of the module is the lowest output voltage. The module operates with no load. At this time, the duty cycle of the module is the minimum. The module should not be damaged after 2 hours of continuous operation;

b. Adjust the input voltage of the module to the undervoltage point+3v, and the output of the module is at the inflection point of the highest output voltage. At this time, the duty cycle of the module is the maximum. The module shall not be damaged after 2 hours of continuous operation;

c. Adjust the input voltage of the module to the input voltage at the lowest efficiency point, and the module output is at the inflection point of the highest output voltage. The module shall not be damaged after 2 hours of continuous operation;

d. Adjust the input voltage of the module to overvoltage point - 3v, and the output of the module is at the inflection point of the highest output voltage. At this time, the duty cycle of the module is the maximum, and the module shall not be damaged after 2 hours of continuous operation;

e. Adjust the input voltage of the module to the input voltage at the lowest efficiency point, and the module output is at the inflection point of the highest output voltage. The module shall not be damaged after 2 hours of continuous operation.

Note: The above tests must be carried out at the maximum operating temperature specified in the specification.

Criteria

Under the above conditions, the module is not damaged and is qualified; Otherwise, it is unqualified.

7. Special waveform test of power supply

Test description

Test the stable operation capability of the power module under the conditions of sharp edge, burr and harmonic that may be caused by grid waveform distortion. The following waveforms must be input for test:

(1) Burr input test waveform

Burr in the power grid is the most common waveform in the power grid, and there is no limit to the size and amplitude of the burr. Generally, the burr input in the power grid can be simulated through the oscillating wave input test and ringing input waveform, but the following burr input tests are required

Features: the power grid spike has overshoot and will drop to 0v. The overshoot and drop pulse width is very narrow, generally not more than 100ms, and the overshoot amplitude is generally not more than 100v. The falling phase is not only limited to the peak point, but can occur in any phase. This kind of waveform is very common in the actual power grid, and opening any switch will cause this phenomenon.

(2) Voltage clipping waveform input

This waveform is also very common in the power grid, which is characterized by: the power grid suddenly drops to 0v from an indeterminate phase, and then recovers until the next half wave starts. In iec 1004-4-11, the drop of waveform starts from more than half a cycle, but there are many similar waveforms with a drop time less than half a cycle in the actual power grid. During the test, it is required that the input voltage waveform drops from 90 °, drops for 1/4 cycle, and works for 2 hours for a long time.

(3) The half wave head of the power grid rises sharply to twice the voltage. This waveform is mainly used to simulate the resonant over-voltage that will suddenly appear in the actual power grid. In this case, the input over-voltage protection line of the module does not work, and this impact is dangerous for the circuit with pfc. Test contents: a. When the input voltage is 180v and the output is full load, simulate the waveform with ac source. 180v is required to work for 3 minutes, then the voltage suddenly increases to 380v for 100ms, and then recovers to 180v. Let the module work for a long time in this case without damage; b. Set the ac source so that the input voltage is 0v, lasting for 5 minutes, then the voltage suddenly increases to 380v, lasting for 100ms, and then recovers to 0v, allowing the module to work for a long time in this case without damage.

test method

AC source is used to supply power to the module, and the module is output with full load; Simulate spike, burr and harmonic voltage input with ac source, and measure input current and output voltage when each special voltage input operates for 2 hours. The module shall be able to operate stably. Pay attention to x capacitor, auxiliary power supply, soft start resistance and other possible problems during the test.

Criteria

It can operate stably without damage under the condition of possible spike, burr and harmonic voltage; Otherwise, it is unqualified.

8. Active pfc performance test

Test description

The power module with source pfc is sensitive to power grid spikes, burrs and harmonics, and should be fully and carefully tested.

test method

The AC source is used as the input voltage source, and the output is with half load and full load respectively. The input current waveform and voltage waveform are tested, and the voltage after pfc is monitored; Test the phase and amplitude relationship of input voltage and current under the condition of sharp, burr and harmonic; Measure the current and voltage of the pfc switch to verify the safety of the switch and other power devices and the ability of the current to track the voltage change in the full voltage range and under the conditions of burrs, spikes, harmonics, etc.

Criteria

Pfc test can be used as reliability reference, and serious problems should be solved in time.

9. Operating voltage test

Test description

There are many switching overvoltages in the power grid, among which the most common time-space load line closing overvoltage also poses a great threat to the module. This test is to verify the module's ability to resist switching overvoltage.

test method

The simulation of overvoltage lines is very simple, and the principle is as follows:

The inductance parameter is 10mh (for reference: in the module test method of ees, there is no grounding capacitance, the input resistance is connected in series with the inductance, the resistance value is 0 ohm, the inductance is 8mh, the resistance is 79 ohm, and the inductance is 10mh), the capacitance is 16.7uf, and the test waveform is as follows (not drawn).

Connect the tested equipment to both ends of the capacitor. At the moment of k closing, overvoltage will be generated at both ends of the capacitor to simulate the damage of overvoltage to the equipment during power on. As a limit test item, the input is connected to l and n lines, and the tested equipment is connected to both ends of the capacitor. The equipment is frequently turned on and off, with a repetition rate of 1 time/5 minutes, and the test lasts for 5 hours. For three-phase input equipment, the input is connected to line l and line l, and the tested equipment is connected to both ends of the capacitor. The repetition frequency is once/5 minutes, and the test lasts for 2 hours.

Criteria

In case of short-term function degradation or performance degradation during the test, but it can recover automatically, it is qualified; However, those with permanent deterioration of performance or requiring manual intervention to recover are unacceptable.

The above is related to the switching power supply test organized by the wound core detection team. I hope it will be helpful to you. Our company has a team of professional engineers and industry elites, and has built three standardized laboratories with an area of more than 1800 square meters, which can undertake a variety of test projects such as electronic component test verification, IC authenticity identification, product design material selection, failure analysis, functional testing, factory incoming material inspection and tape weaving.