Abstract: This article briefly describes the output anomaly problem, a common issue in switching power supply applications, and analyzes its causes. It also provides corresponding verification methods, solutions, and prevention measures to reduce the likelihood of output anomalies in different applications and improve system reliability.
introduction:
In their daily work, engineers often encounter the following power output abnormalities:
(1) The power supply is nominally 24V, so why wasn't it 24V during testing?
(2) Why do the measured values of parameters such as ripple and noise from the power supply exceed the values specified in the manual?
(3) The input voltage is normal, but after working for a while, why does the output disappear?
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This article will summarize common output anomaly issues, analyze their causes, and provide corresponding solutions.
Common output anomalies
As an essential core component of electrical equipment, power supplies typically require stability, reliability, high precision, and high performance, specifications of which can be found in their technical manuals. However, during testing in laboratories or practical applications, we often find discrepancies between the test parameters and the nominal parameters. This usually occurs in the following situations:
1. Output voltage is too low or too high;
2. Output ripple noise exceeds specifications;
3. No output after working continuously for a period of time;
When we encounter these problems, how do we analyze, identify, and eliminate them? We will analyze each problem one by one below.
1. Output voltage is too low or too high
Generally, there are two reasons why the output voltage is too low or too high:
1) Accidentally touching the adjustable resistor:
Method of determination: A multimeter can be used to directly measure the voltage at the output terminals to determine whether it is the standard output voltage;
Solution: Rotate the adjustable resistor according to the direction shown on the label to appropriately increase the output voltage to meet the actual needs;
2) The line 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 voltage at the power supply output terminal and the voltage at the customer load input terminal;
Solution: It is recommended to shorten and thicken the traces between the power supply and the load;
2. Output ripple noise exceeds specifications.
There are generally three reasons why the output ripple noise exceeds the specifications:
1) The ground loop introduces high-frequency signal interference, and the oscilloscope bandwidth setting is too large.
Judgment method: Check whether the method for testing ripple noise conforms to the recommended method and wiring method in the technical manual;
Solution: Use the correct testing methods. Inappropriate methods can distort the results and lead to misinterpretations. Typically, bandwidth is limited during ripple noise testing, primarily depending on the operating frequency of the module under test. For example, power supply modules usually operate below 500kHz, and their switching noise frequencies are mostly below 5MHz. Therefore, it is recommended to limit the bandwidth to within 20MHz during testing to ensure that the measured ripple noise reflects the actual power supply output. Additionally, to avoid introducing interference from the oscilloscope's power supply ground pin during testing, it is recommended to cut off the ground pin on the oscilloscope's power cable.
The conventional testing methods are the parallel line test method and the proximity test method. The parallel line test method is as follows:
In the diagram, capacitor C1 is a ceramic capacitor; C2 is an electrolytic capacitor. By default, C1 and C2 are 1uF and 10uF respectively.
The reliability test method is as follows:
Compared to conventional wire-spinning tests, the proximity test method primarily reduces the area of the ground loop, preventing interference from coupling into the ground loop during testing and affecting the results. The main method, as shown in the diagram, involves removing the ground clip and directly using the copper ring on the probe as ground. This effectively avoids the influence of the external electromagnetic environment on the test.
2) Short the neutral wire or input ground of the isolation power module to the negative terminal of the output.
Troubleshooting methods: Check if the power module's neutral (N) line/input ground is shorted to the output ground; check if the load board at the rear has a negative grounding point.
Solution: It is not recommended that customers connect the N line/input ground and output ground of the isolation power module together. If the actual application requires the negative terminal to be grounded and the requirements for EMC, ripple noise are not high, or there are no requirements for isolation voltage, it can be used with a common ground.
3) There are high-power, high-interference devices or components near the power module.
Solution:
a. The customer's system layout keeps the power module away from high-power equipment;
b. Add a filtering peripheral circuit to the front end of the power module;
c. Shorten the output leads of the power module to reduce noise coupling; if possible, use a metal casing to shield against external interference.
<Click to learn more about EMC>
3. No output after working continuously for a period of time.
There are generally two reasons why there is no output after working continuously for a period of time:
1) When the ambient temperature is too high and the load is not derating, the power supply enters over-temperature protection after operating for a period of time.
Judgment method: Measure the ambient temperature and actual load conditions of the product in actual use, and compare them with the derating curve in the technical manual;
Solution: a. Recommend that the customer use a higher power product or derating it according to the technical manual to meet high-temperature requirements;
b. The layout near the power supply should be as dispersed as possible, ventilation holes should be added to the customer system casing, and additional heat dissipation measures should be implemented if necessary;
2) Device damage
Judgment method: a) First, visually inspect the entire defective product for any burnt parts, damaged parts, or loose or missing solder joints;
b. Use a multimeter to check for short circuits at the product's input and output terminals, and to check if the fuse is open;
Solution: If you encounter any of the above issues (a) or (b), please contact our sales staff for factory inspection and repair.
3) The output indicator light is not lit or is very dim.
Possible causes: Accidental activation of the adjustable resistor resulted in a very low output voltage, causing insufficient current to the LED.
Test method: Rotate the adjustable resistor in the direction shown on the sticky note to increase the output voltage, and verify whether the light becomes brighter;
Solution: Increase the output voltage appropriately to meet actual usage requirements;
Summarize
This article briefly describes common output anomalies in switching power supply applications, analyzes the causes of these problems, and provides corresponding verification methods, solutions, and prevention measures to reduce the possibility of output anomalies in different applications and improve system reliability. If you encounter any problems during use, please contact our sales or technical personnel for specific solutions.
With a professional sales and technical service team, Jinshengyang serves its customers by providing pre-sales selection, in-sales technical communication, and after-sales professional support, offering one-stop solutions.
