NB/T 10296-2019Technology specification of AC-DC switching power supply for feedback loop (English PDF)

3.1 Feedback loop

In the system, the output power (voltage or current) is fed back to the input path.

3.2 Bode plot

Graph composed of logarithmic amplitude-frequency characteristics and logarithmic phase-frequency characteristics.

3.3 Phase margin

The difference between the phase value when the gain is 0dB and -180° on the system Bode chart.

3.4 Gain margin

The difference between the corresponding gain value and 0 dB when the phase is -180° on the system Bode chart.

3.5 Slow loop channel

The voltage divider network branch of the three-terminal programmable voltage divider regulator.

3.6 Fast loop channel

The branch connecting the optical couple LED and the three-terminal programmable voltage divider regulator.

3.7 Vector sum

A mathematical operation performed on the fast loop channel data and the slow loop channel data to obtain the final Bode plot.

4.1 Judgement of feedback loop stability

In order to ensure the stable operation of the switching power supply, the judgment requirements for the stability of the feedback loop are as follows.

--Phase margin > 45 °;

--Gain margin < -10 dB.

5.1 Test environmental conditions

Except for climate environment test and reliability test, other tests in this standard can be carried out under the following standard atmospheric conditions for tests.

5.2 Test requirements

5.2.1 General requirements

The product should generally be warmed up for 15 minutes before the feedback loop test, and tested under light load, half load and full load conditions.

--Frequency coverage. 10 Hz~500 MHz;

--Narrow bandwidth. 2 Hz~30 kHz;

5.2.2 The requirements for the AC regulated power supply used in the test are as follows.

5.2.3 The requirements for the test network analyzer are as follows.

--High frequency resolution. 1 MHz;

--Scan mode. logarithmic scan;

--Display mode. gain and phase mode;

--Small excitation source power. output power -60 dBm~20 dBm.

5.3 Feedback loop test under normal temperature conditions

5.3.1 General

The feedback loop is generally composed of a fast loop channel and a slow loop channel, and the test result is the combined value of the two. The requirements for isolation transformer T1 are as follows.

--The turns ratio between primary and secondary is 1.1;

--Frequency coverage 10 Hz~500 MHz;

--The impedance cannot be significantly lower than 50ohm;

- There should be no resonance point in the test frequency range, and it should show inductance.

In order to verify the accuracy of the measurement, a through calibration is required before the test.

Note 2. The R channel is used to measure the signal injected into the loop, and the A channel is used to measure the output signal of the loop. A/R is the open loop characteristic of the loop.

5.3.2 The schematic diagram of the fast loop channel test is shown in Figure 1.

5.3.2.1 The test procedure is as follows.

1) Under normal temperature (23±2)°C, inject the excitation source signal of the network analyzer at the connection point of the fast loop channel and the circuit, the excitation source The strength of the signal is related to the output voltage of the switching power supply and is set according to the specific conditions of the product;

2) Disconnect the slow loop channel from the circuit, and bias a DC power supply with the same voltage as the output;

3) Set the output load conditions, input voltage and frequency, and turn on the power supply.

After the test is completed, you can get the fast loop channel Bode diagram from the network analyzer screen, including the gain frequency curve and the phase frequency curve.

It is a curve composed of multiple frequency points sampled by a computer. Suppose the complex function expression of this curve is.

5.3.3 The schematic diagram of the slow loop channel test is shown in Figure 2.

5.3.3.1 The test procedure is as follows.

a) Under the condition of normal temperature (23±2)°C, inject the excitation source signal of the network analyzer at the connection point of the slow loop channel and the circuit to stimulate The strength of the source signal is related to the output voltage of the switching power supply, which is set according to the specific conditions of the product;

b) Disconnect the fast loop channel from the circuit, and bias a DC power supply with the same voltage as the output;

c) Set the output load conditions, input voltage and frequency, and turn on the power supply.

After the test is completed, you can get the slow loop channel Bode plot from the network analyzer screen, including the gain frequency curve and phase frequency curve.

It is a curve composed of multiple frequency points sampled by a computer. Suppose the complex function expression of this curve is.

5.3.4 Vector composition

In order to obtain the final Bode plot synthesized by the fast loop channel and the slow loop channel, we must combine the data at each sampling point in vector Assuming that the expressions of the fast loop channel and the slow loop channel sampled at the same frequency are Z1 and Z2 respectively, then the synthesized expression is.

5.3.5 Loop test under low temperature conditions

Under the condition of 0 °C or the lower limit of operating temperature declared by the manufacturer of the power supply product, in accordance with the regulations of 5.3.1, 5.3.2, 5.3.3 and 5.3.4 Test the stability of the feedback loop.

5.3.6 Loop test under high temperature conditions

Under the condition of 45 °C or the upper limit of the operating temperature of the power supply product declared by the manufacturer, in accordance with the provisions of 5.3.1, 5.3.2, 5.3.3 and 5.3.4 Test the stability of the feedback loop.

5.3.7 Loop test under near-field radio frequency electromagnetic field immunity test conditions

When testing the near-field radio frequency electromagnetic field immunity test of the test sample, test the feedback loop in accordance with the provisions of 5.3.1, 5.3.25.3, and 5.3.4 stability.

The conditions and methods of the near-field radio frequency electromagnetic field immunity test are carried out in accordance with Appendix B, and the test level selects level 1.

A.1 Failure definition and explanation

With reference to the provisions of GB/T 5271.14, one of the following conditions shall be regarded as failure.

--Under the specified conditions, one or several performance parameters of the test sample exceed the specified requirements;

--The test sample works within the specified stress range, due to damage or failure of mechanical parts, structural parts, or failure of components Therefore, the test sample cannot complete its specified function.

A.2 Fault classification

A.2.1 Correlation failure

Correlation failures are expected failures of the test sample, which are usually caused by the conditions of the product itself. It is explaining the test results And failures that must be included in the calculation of reliability characteristic values.

A.2.2 Non-related failures

Non-relevant failures are unexpected failures in the test sample. Such failures are not caused by the conditions of the product itself, but test requirements Non-relevant faults caused by other factors shall not be included in the interpretation of test results and calculation of reliability characteristic values. But it should be recorded in the test so that Refer to when analyzing and judging.

A.3 Correlation failure criterion

The following faults are related faults.

--The components, parts, etc. must be replaced to restore the normal operation of the system;

-Only repair, adjust the connector, cable, plug or eliminate the short circuit and poor contact in order to resume normal operation;

--Not caused by the same factor, but two or more (including two) failures occur at the same time, should be recorded as two or more Connectivity failure. If it is caused by the same factor, no matter how many failures occur, it will be recorded as a correlation failure;

--Due to the test sample itself, the safety of the test, maintenance and user personnel is endangered during the test, or the test sample equipment is caused Seriously damaged fault. Once it appears, it should be rejected or unqualified immediately.

A.4 Non-related failure criteria

The following faults are non-related faults.

--Due to changes in test conditions that exceed the specified range (too large fluctuations in the power grid, too large temperature fluctuations, severe electromagnetic interference, mechanical shock, vibration Malfunctions, etc.);

--The prototype fails due to human error;

-Replacement of components and parts due to misjudgment, or failure due to human factors during the overhaul;

--According to the relevant technical regulations of the product, the allowable adjustment parts (parts, components, etc.) are not adjusted properly and caused by failure;

-The failure is determined to be caused by a software program error;

--If there is an abnormal situation, it can automatically resume normal operation after 0.5 hours of shutdown without repairs. This type of incident has occurred three times in total. It is recorded as a non-related failure;

--Failures that occur outside the life span of components that have life index requirements.

A.5 Judgment

The unit undertaking test and inspection can make related or non-related failures based on failure analysis and product standards and related standards determination.

B.1 Test purpose

At present, switching power supplies are growing rapidly with the vigorous development of mobile radio frequency terminal products. Since the switching power supply is often connected with the RF terminal When used together under close distance conditions, the RF interference intensity of the RF terminal received by the switching power supply is far greater than the interference intensity specified in GB/T 17618.

The main purpose of this appendix is to establish a test method and evaluation basis for evaluating the immunity of the switching power supply when it is close to the radio frequency terminal.

B.2 Test principle

The basic principle of this experiment is to simulate the emission of electromagnetic waves of frequencies such as walkie-talkies and mobile phones through a small antenna.

Then put the antenna close to the sample to be tested and monitor the working status of the sample to be tested, so as to evaluate the short-distance of the sample to be tested to the RF product.

Anti-interference ability. The block diagram of the test principle is shown in Figure B.1. Figure B.1 Block diagram of test principle

B.3 Test level

Taking into account the need to cover the frequencies generated by walkie-talkies, mobile phones, etc., set the test level as shown in Table B.1.

B.4 Test equipment

The test equipment shall meet the following requirements.

Anechoic chamber. the recommended size is shown in Figure B.4, where. Both the measured object and the measuring antenna can guarantee.

--Minimum distance between antenna and absorbing material. 0.5 meters;

--Minimum distance between antenna and shielding wall. 1.5 meters.

Electromagnetic interference filter. The cable entering the laboratory must use a filter, and ensure that the filter does not cause resonance effects on the connection line.

RF signal generator. can meet the frequency band requirements and modulation requirements in Table B.1.

Power amplifier. amplify the signal and provide the required field strength level for antenna output. The level of harmonics and distortion generated by the amplifier should be The level is at least 15 dB lower. Transmitting antenna. The antenna must meet the following requirements.

--Bandwidth. 360 MHz~2.7 GHz;

--Input power. 20 W maximum.

Auxiliary equipment for recording power level. used to record the power level required for the specified field strength of the experiment and control the level of the test field strength. should Ensure that auxiliary equipment has sufficient immunity.

Due to the high field strength of the signal generated by the test, the test should be carried out in a shielded room in order to comply with the regulations prohibiting interference to wireless communications. The main requirements of the shielded room are as follows.

--Measure according to the measurement method specified in GB/T 12190, and its shielding performance index meets the requirements of Table B.2.

B.5 Field calibration

The purpose of field calibration is to ensure that the field around the sample to be tested is sufficiently uniform to ensure the validity of the test results. No progress during calibration Line modulation to ensure that the sensor indicates normal.

Before the test, arrange in accordance with the requirements of Figure B.3.Any position of the antenna is at least 500 mm away from the absorbing material, and the distance from the ground plane Surface, antenna cable, and laboratory shielding layer must be at least 1,000 mm.

B.6 Test arrangement

The samples to be tested should be placed on an insulation test platform with a height of 0.8 m, and run as far as possible under actual working conditions.

Wiring should be carried out in accordance with the procedures recommended by the manufacturer. If not specified, unshielded parallel wires should be used.

B.7 Test procedure

The samples to be tested should be tested under predetermined operating and climatic conditions. The temperature and relative humidity should be recorded in the test report.

The antenna is above the sample to be tested and parallel to the ground plane. Take the sample to be tested to the auxiliary test equipment and the connecting line as the center line The wave moves at a constant speed. Before the test, the area covered by the antenna operation should be determined according to the size of the sample to be tested, the accessory equipment and the wiring harness connected to it product.

In order to make the sample to be tested and accessory equipment completely covered in the electromagnetic field environment generated by the antenna, set the distance between the sample to be tested and the antenna When the distance is 5 mm, the step distance is 30 mm.

Each surface of the sample to be tested shall be tested with a spacing of 5 mm. At the same time, the antenna is divided into two directions perpendicular to each other.

Apply the interference signal shown in Table B.1 at the antenna end. The detailed test procedure is as follows.

a) Place the antenna parallel to the sample to be tested and the wire harness, and set the trajectory parameters of the antenna operation according to the distance from the antenna to the sample to be tested.

Count, let the antenna move along the square wave trajectory shown by the dotted line in Figure B.5 above the sample to be tested, accessory equipment and wiring Check the working status of samples; Figure B.5 Antenna movement track diagram (placed in parallel)

b) Rotate the antenna horizontally by 90 °, and repeat step 1, as shown in Figure B.6; Figure B.6 Antenna movement track diagram (vertical placement)

c) If the sample to be tested can be placed and used in different directions (such as vertical or horizontal), all sides should be tested. Every facet Repeat steps 1 and 2 to complete the tests;

d) During the test, try to make the sample to be tested fully run as much as possible, and conduct the immunity test in all selected sensitive operating modes Test. The following implementation procedures are recommended.

The test is carried out according to the test plan, which should be included in the test report. The test plan includes the following.

--The size of the sample to be tested, including the length of the connecting harness from the sample to be tested to the simulated load and the size of the simulated load;

--Working mode of samples to be tested;

--The layout of the test, including the height of the table and the antenna operating track parameters;

--The type of antenna used;

--Applicable test level;

--Acceptable performance criteria.

In order to determine some items of the test plan, some preliminary tests may be required.

The test report shall include test conditions, calibration instructions and test results.

B.8 Evaluation of test results

The test results should be classified according to the loss of function or performance degradation of the sample to be tested. These classifications are consistent with those specified by the manufacturer and test applicant, Or the performance level agreed between the manufacturer and the user. The recommended classification is as follows.

--The performance is normal within the technical specification limits specified by the manufacturer or the client or the customer;

--The function is temporarily lost or the performance is temporarily reduced, but after the harassment stops, the sample to be tested can recover by itself without operator intervention;

--The function is temporarily lost or performance is temporarily reduced, but the operator's intervention is required to return to normal;

--Due to hardware or software damage, or loss of data, the function that cannot be restored to a normal state by itself is reduced or lost.

The manufacturer's technical specifications may specify which of the effects to be tested samples are negligible and which are acceptable.

B.9 Test report

The test report should contain all the information that can reproduce the test. Especially the following.

--Content specified in the test plan;

--Identification of samples and auxiliary equipment to be tested, such as brand name, product model and serial number;

--Test equipment identification, such as brand name, product model and serial number;

--Any special environmental conditions required for testing, such as shielded room; -Any specific conditions necessary for the test;

--The performance level specified by the manufacturer, client or purchaser;

--The influence and duration of the test samples observed by the laboratory during or after the harassment test;

--The judgement basis for test pass/fail;

--Any special conditions used, such as cable length, type, shielding or grounding conditions.