This time delay is measured as an angular difference, and it is defined as the degree of phase shift. If the delay between the feedback and control circuit approaches a critical value at its unity-gain crossover, the power supply gets unstable and starts oscillating. The constant-voltage power supply has a built-in feedback loop that continuously monitors and stabilizes the output voltage by changing the duty cycle accordingly. In contrast, power supply testing in production environments primarily focuses on overall function based on the specifications determined during the product design phase. These tests require high-performance test equipment with a proper control environment. For example, the test setup in a design lab is done to verify design parameters. As a result, the test performance needs to be different depending on the application. Power supplies are used in a variety of products. Other than that, a typical flyback converter needs a minimum load to work properly otherwise the output voltage cannot be regulated properly. The situation connecting a test instrument in the primary section will cause a short circuit to the ground, which can permanently damage the test instrument. In a test situation where the secondary section is connected to earth ground and the primary section is floating. In the schematic, it is denoted as T1, the transformer T1 in conjunction with the optocoupler OK1 provides isolation from the primary side. One of the most important parameters to take note of is the transformer section. The test operator has to be extra careful in this section. As the main switching transistor is responsible for driving the main transformer, it is most likely to get very hot, and as it comes with a TO-220 package there's a chance that the hit sink will have high voltage on it. The switching transistor T2 is the main switching transistor, and T1 is the auxiliary switching transistor. Before we proceed with any testing of the SMPS circuit, this capacitor needs to be discharged properly. Engineers and technicians should be very careful while working with these potentially lethal voltage levels.Īnother thing to be very cautious about is the filter capacitor C2, as it holds the charge for a long time, even when the power supply is disconnected from the mains. In the high voltage side, we have a fuse as a protection device, then the mains voltage is rectified and filtered by the input rectifier diodes D1, D2, D3, D4, and capacitor C2, this means the voltage level in between those lines can reach more 350V or more at a given point in time. The schematic was made to understand the high voltage side and low voltage side clearly. The above schematic shows a line-powered power supply which utilizes the flyback topology to convert high voltage DC to low voltage DC.
But doing so introduces safety concerns that can be harmful to the device if not taken care of.
Switched-mode power supplies (SMPS) circuits normally switch very high voltage DC with an auto adjustable duty cycle, in order to regulate the output power with high efficiency. Basics of SMPS Testing – Points to Remember If you are an SMPS Design Engineer, you can also check out the article on SMPS PCB Design Tips and SMPS EMI Reduction Techniques both of which we discussed earlier. The following examination gives you an idea about the most basic power supply architectures and their testing process.
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In this article, we will learn how to test SMPS circuit and talk about some of the most basic tests for SMPS and the safety norms that need to be followed to test an SMPS circuit easily and efficiently. It is necessary to gather better knowledge about the SMPS testing requirements to fulfill product standards. To verify product functionalities and design parameters, a power supply circuit requires sophisticated testing methods and electronic test equipment.
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