Test plan of the hottest switching power supply

Switching power supply test scheme

Abstract: in today's working environment of electronic products, switching power supply has been widely used. This paper analyzes the test of switching power supply, and introduces the test items and methods of switching power supply

switching power supply is widely used in electronic enterprises because of its high efficiency and small size. The following are the test methods and test items I summarized in my work. If these aspects can be fully considered in the power supply design, its products will be used by more and more customers

the requirements of current electronic products for power supply have been improved. Most of them are concerned about its stability, the range of input voltage, output stability, and the size of output harmonics. It is found that some power supplies have large ripple during work, which leads to the equipment not working. Therefore, this is also an aspect that affects the development of power supply

in the actual work of the power supply, among the requirements of the circuit for the applicability of materials, the most concerned is the source effect (voltage regulation rate), because after the circuit is determined, the load has been basically determined, and the impact of the load is significantly less than that of the input voltage on the power supply. In addition, pay attention to electromagnetic interference. In the electronic environment, electromagnetic interference will have a certain impact on the work of the power supply, and the power supply with small source effect and load effect has better stability, These aspects should be considered in the power supply design

with the implementation of national compulsory certification, electromagnetic interference and electromagnetic anti-interference technology are gradually put on the agenda. The design of new power supply should pass the electromagnetic compatibility test. We will create materials that can withstand increasingly harsh temperature and pressure conditions, so as to ensure the flow of products in the market

I. test items

the items to be tested include no-load output of switching power supply, voltage and current output at rated load, source effect, load effect, ripple, withstand voltage and insulation resistance, short-circuit protection (or overcurrent protection point)

the test is carried out with reference to the detailed parameter instructions given by each switching power supply

for the more important power supply or the power is more than tens of watts, its efficiency (or the working temperature of the internal power device) directly determines its reliability and failure rate, which should be tested; In addition, there are many other indicators that should be tested according to different requirements, such as the instantaneous drop of output voltage of sudden load and its recovery time, the input power factor and waveform peak ratio of ac/dc power supply, various EMC indicators of power supply, temperature coefficient, time stability, etc

II. Test requirements

1. The tester should be able to correctly use the digital multimeter, identify the pin diagram of the switching power supply, adjust the output voltage of the power supply, and have electrical related knowledge

2. It is required to use instruments with high precision and resolution as much as possible, and choose to use instruments according to the actual situation

3. Generally, the routine test is carried out under normal temperature and pressure. If there are special requirements for the test conditions, the test should be carried out under the required conditions (for example, some need to simulate the environment of the work site, such as outdoor, rainy, exposed to the sun, etc.)

III. test method and process

3.1 no load output voltage

adjust the input voltage of the switching power supply to the rated voltage of the switching power supply, and test the output voltage of the switching power supply with a multimeter. In order to reduce the error, several groups of data can be measured (the power supply switching power supply in the figure represents the detected switching power supply)

Figure 1 Schematic diagram of no-load wiring

3.2 switching power supply output under rated load

this step of test includes the test of rated output voltage and current. First, determine the rated load of switching power supply, and generally select resistance as the load. Note that the power of the selected resistor must be much greater than the output power of the switching power supply to reduce the heating of the resistor. Some heat dissipation measures can also be added, such as placing exhaust fans

calculation formula of rated load:

r0=u2/p

note: in the formula, R0 is the rated load resistance value, u is the nominal output voltage value, and P is the rated power

after determining the rated load, connect the rated input voltage of the switching power supply, connect the load circuit of the switching power supply, connect an ammeter in series in the load circuit (as a safety meter, it is recommended to use a precision shunt resistor in series to measure its voltage drop and convert it into current value), test the current in the circuit, and test the output voltage of the switching power supply with the multimeter voltage range. And record the voltage and current value. The wiring diagram is shown in Figure 2, where R0 is the rated load

Figure 2 wiring schematic diagram of rated load

3.3 source effect (i.e. voltage regulation rate)

source effect is the change of output voltage relative to nominal output when the input voltage changes from low to high within the input voltage range of switching power supply

adjust the input voltage of the switching power supply to the lower limit and upper limit of the range respectively, and measure the output voltage of the switching power supply with a multimeter and record it

Figure 3 source effect test

the calculation formula is: [(vo1-vo2)/vo]*100%

note: Vo1 is the output voltage value measured when the input voltage and the upper limit of real-time graphic dynamic switching in the test, VO2 is the output voltage value measured when the input voltage is lower limit, VO is the nominal output voltage

3.4 load effect (i.e. current regulation rate)

load effect is the change of the output voltage of the switching power supply relative to the nominal value when the load changes from rated load to half load (or 20% load) under the rated voltage operation of the switching power supply

the important task in this step is to determine the load. The percentage of load is calculated according to the current, that is, the percentage of half load (or 20% load) current in the rated current. According to the calculated current value, infer the resistance value for selection

load calculation formula under half load:

r1= (u2/p) *2

note: R1 is the load resistance under half load, that is, twice the rated load

R1 in the figure is the inferred equivalent load

Figure 4 load effect test

the calculation formula is: [(VO '- V amount)/vo]*100%

note: VO' is the output voltage of the switching power supply measured after the resistance equivalent in percentage is connected to the output circuit of the switching power supply, V amount is the output voltage of the switching power supply measured under the rated load, and VO is the nominal output voltage

3.5 ripple

under the condition of switching power supply from no-load to full load, multi-point or continuous and uniform variation (generally testing ripple under no-load, half load and full load), adjust the oscilloscope to 20MHz, AC coupling mode, appropriate scanning cycle, clamp the grounding clamp of the oscilloscope to the GND end of the switching power supply output, contact the VO end of the switching power supply output with a probe, and read out the peak value of the maximum ripple in the oscilloscope

Figure 5 ripple test

for ac/dc power supply, it should be observed under full load and the scanning speed of oscilloscope can display several AC cycles. The "bandwidth attenuation" of the oscilloscope should be turned off (no attenuation)

3.6 withstand voltage and insulation resistance

withstand voltage is tested with a withstand voltage tester. According to the technical data given by the switching power supply, find out the reference value of withstand voltage, turn on the power supply of the withstand voltage tester, and set parameters, including AC/DC, range, leakage current and time settings. After setting, start the withstand voltage tester and observe the over leakage alarm. If the over leakage alarm is given, select a small leakage current, increase the leakage current or reduce the test voltage. It is necessary to test the withstand voltage between 1, 4 and 1, 2 and 3, 4 respectively

Figure 6 withstand voltage test

insulation resistance is likely to be tested with a useful megger with these properties. Clamp both ends of the megger with appropriate working voltage to the two ends that need to be tested, quickly shake the handle until the clutch slips, read out the meter value, or use an electronic megger for testing

3.7 short circuit protection characteristics (or overcurrent protection points)

this depends on the instructions given in the technical data. For example, the description of the switching power supply is: the short circuit protection characteristics are long-term self recovery, which can be tested by connecting a wire to the output end of the switching power supply, and the voltage output during short circuit and the switching power output after short circuit elimination can be observed for a long time (determined according to needs)

Figure 7 overcurrent protection point test reference circuit

in the figure, R3 represents a current that can produce twice the rated load (that is, at this time, the resistance value of R3 is half of the rated load), vo+ and vo- are connected to the positive and negative output terminals of the switching power supply respectively

the meaning of overcurrent protection point is that when the current in the circuit reaches a certain value, the switching power supply will cut off the output (it must be noted that some switching power supply overcurrent protection is not cut-off type, but may be current limiting type). Put variable loads in series in the output circuit of the switching power supply (the variable range is required to be large enough), and adjust the current in the circuit by adjusting the variable load. During the current rise, pay attention to the reading of the ammeter, and read the value before the current changes to 0 (or a minimum or smaller value), It is the over-current protection point of switching power supply (at this time, pay attention to the heat dissipation of resistance, because the resistance heats up more under the condition of over-current than under the rated output)

IV. test record and data processing

each step of the test should record the data and abnormal conditions in detail, and if there are abnormal conditions, analyze the reasons. The data is recorded for calculation parameters and evaluation of switching power supply

data processing:

1. Average value processing

2. Source effect calculation

formula is:

[(vo1-vo2)/vo]*100%

note: Vo1 is the output voltage value measured at the upper limit of input voltage, VO2 is the output voltage value measured at the lower limit of input voltage, and VO is the nominal output voltage

3. Calculation of load effect

the formula is:

[(VO '- V amount)/vo]*100%

note: VO' is the output voltage of the switching power supply measured after the resistance equivalent in percentage is connected to the output circuit of the switching power supply, V amount is the output voltage of the switching power supply measured under the rated load, and VO is the nominal output voltage

about the author: Shang Kaiming, Henan brilliant Technology Co., Ltd., is engaged in hardware design and testing

email: shangkaiming@

address: No. 74, science Avenue, high tech Development Zone, Zhengzhou City

postal code: 450001

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