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Common problems with power supply applications: abnormal output

Article Source：Kinri Energy | Author：Kinri Energy | Issuing Time：2024.05.07
Abstract: This article briefly describes the common problems of output abnormalities in the application of switch mode power supplies, and analyzes the causes of the problems. At the same time, corresponding verification methods and solutions and preventive measures are provided to reduce the possibility of output abnormalities in different applications of power supplies and improve system reliability.

Introduction:

In daily work, engineers often encounter the following problems with abnormal power output:

(1) Why is the nominal 24V power supply not 24V during testing?

(2) Why does the measured ripple noise and other parameters of the power supply exceed the nominal values in the manual?

(3) The input voltage is normal, but after working for a while, why is the output gone?

......

This article will sort out common output anomalies, analyze their causes, and provide corresponding solutions.

Common abnormal output phenomena of power supply

As an essential core component of electrical equipment, power supply is usually expected to be stable, reliable, high-precision, and high-performance. These indicators can be found in its technical manual. But when we test in the laboratory or practical applications, we often find that the test parameters do not match the nominal parameters. There are usually the following situations:

1. Low or high output voltage;

2. Output ripple noise exceeds specifications;

3. No output after continuous work for a period of time;

How should we analyze, confirm, and troubleshoot these issues when we encounter them? Next, we will analyze each problem one by one.

1. Low or high output voltage

Usually, there are two reasons for low or high output voltage:

1) Mistakenly touching an adjustable resistor:

Judgment method: Use a multimeter to directly measure the output terminal voltage and determine whether it is a standard output voltage;

Solution: The adjustable resistor can be rotated according to the direction on the label paper, and the output voltage can be appropriately increased to meet practical needs;



2) The distance between the customer's load and the power supply is too long, resulting in excessive output line loss

Judgment method: Test and compare the output voltage of the power supply and the input voltage of the customer's load;

Solution: It is recommended to shorten and thicken the wiring between the power supply and the load;

2. Output ripple noise exceeds specifications

Usually, there are three reasons why output ripple noise exceeds specifications:

1) The ground wire ring introduces high-frequency signal interference, and the oscilloscope bandwidth is set relatively large

Judgment method: Check whether the method of testing ripple noise complies with the recommended methods and wiring methods in the technical manual;

Solution: Use the correct testing method. Inappropriate testing methods can cause testing distortion, leading to misjudgment of results, and other issues. Usually, during ripple noise testing, we limit the bandwidth, which mainly depends on the operating frequency range of the tested module. Taking the power module as an example, the operating frequency of the power module is usually below 500KHz, and the frequency of switch noise is mostly below 5MHz. Therefore, during the testing process, it is recommended to limit the bandwidth to within 20MHz to ensure that the tested ripple noise is generated by the real power supply. At the same time, during testing, to avoid interference on the ground wire of the oscilloscope's power supply, it is recommended to cut off the ground pin of the oscilloscope's power supply wire.

Compared to conventional wire testing, relying on the measurement method mainly reduces the area of the ground wire loop to avoid coupling interference in the ground wire loop during the testing process, which affects the test results. The main method is to remove the ground clamp as shown in the figure and directly use the copper ring on the probe as the ground. This can effectively avoid the impact of external electromagnetic environment on testing.

2) Isolation power module N-line or input ground short circuited to output negative pole

Method of judgment: Check if the power module's N line/input ground output ground is short circuited, and check if there is a negative grounding point on the backend load board;

Solution: It is not recommended for customers to connect the N line/input ground - output ground of the isolated power module together. If the actual application requires negative grounding and does not have high requirements for EMC, ripple noise, or isolation voltage, it can be used together;

3) There are high-power, strong interference devices or components near the power module

Solution:

a. The customer system layout keeps the power module away from high-power equipment;

b. Add filtering peripheral circuit to the front end of the power module;

c. Shorten the output lead of the power module to reduce noise coupling, and if necessary, use a metal shell to shield external interference;

3. No output after continuous operation for a period of time

There are generally two reasons why there is no output after continuous work for a period of time:

1) If the ambient temperature is too high and the load is not derated, the power supply will enter over temperature protection after working for a period of time

Judgment method: Measure the actual environmental temperature and load situation of the product used, and compare it with the derating curve in the technical manual;

Solution: a Suggest customers to use higher power products or reduce the rating according to the instructions in the technical manual to meet high-temperature usage;

2) Device damage

Judgment method:

a. Firstly, visually inspect the entire defective product to see if there are any burnt components, damaged components, or virtual solder leaks in the components;

b. Use a multimeter to check if there is a short circuit at the input and output terminals of the product, and if the fuse is already open;

Solution: If the above phenomena a and b are found, contact our sales personnel and return to the factory for inspection and repair;

3) The output indicator light is not on or very dark

Possible reasons: Mistakenly touching an adjustable resistor leads to low output voltage and insufficient LED current;

Method of judgment: Rotate the adjustable resistor according to the direction on the sticky note to increase the output voltage, and verify whether the light will turn on;

Solution: Increase the output voltage appropriately to meet practical usage needs;

Summary

This article briefly describes the common problems of output abnormalities in the application of switch mode power supplies, and analyzes the causes of the problems. At the same time, corresponding verification methods and solutions for prevention are provided to reduce the possibility of output abnormalities in different applications of power supplies and improve system reliability. If there are any problems during use, you can contact our sales or technical personnel to provide corresponding solutions for specific problems.

Kinri Energy serves customers with a professional sales and technical service team, providing pre-sales selection, technical communication during sales, and professional after-sales support, providing customers with one-stop solutions.
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