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The design method of bare board power module is introduced, come and collect!
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2022-11-04 09:21
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The electromagnetic interference level of bare board power module is the most difficult part in the design. The most designers can do is to fully consider the design, especially in the layout. Because DC-DC converters are very commonly used, hardware engineers will be more or less exposed to related work. The following is an introduction to the design method of bare board power module.
In the design of bare board power modules, even ordinary DC-DC switching converters will have a series of problems, especially in the design of high-power power supplies. In addition to functional considerations, engineers must ensure the robustness of the design to meet the requirements of cost targets, thermal performance and space constraints, while ensuring the design schedule. In addition, considering the product specifications and system performance, the electromagnetic interference (EMI) generated by the power supply is sufficiently low. However, the electromagnetic interference level of the power supply is the most difficult item in the design to predict accurately. Some people even think that this is impossible. The most designers can do is to fully consider the design, especially the layout.
Although the principles discussed in this article are applicable to a wide range of power supply designs, we will only focus on DC-DC converters here, because its applications are quite extensive, and almost every hardware engineer will be exposed to related work, and it may be necessary to design a power converter. In practical applications, it is likely to encounter odd harmonic emission and even harmonic emission at the same time. If only odd harmonics are generated, the duty cycle of the waveform is accurate to 50%. However, bare board power modules rarely have such duty cycle accuracy.
The electromagnetic interference amplitude of series harmonics is affected by the on-off of Q1 and Q2. When measuring the rise time tr and fall time tf of the drain-source voltage VDS, or the rise rate di/dt of the current flowing through Q1 and Q2, This can be clearly seen, which also means that we can reduce the level of electromagnetic interference by reducing the switching speed of Q1 or Q2. In fact, extending the switching time does have a great impact on harmonics with frequencies higher than f = 1/tr, but at this time a compromise is made between increasing heat dissipation and reducing loss. Nevertheless, the bare board power module controls these parameters. It is still a good method, which helps to strike a balance between electromagnetic interference and thermal performance, which can be achieved by adding a small resistance (usually less than 5), this resistor may be connected in series with the gates of Q1 and Q2 to control tr and tf. You can also connect the "turn-off diode" in series with the gate resistor. With the individual control conversion time tr or tf, in fact, this is an iterative process. Even the most experienced power supply designers use this method. Our ultimate goal is to reduce electromagnetic interference to an acceptable level by slowing down the switching speed of the transistor, while ensuring that its temperature is low enough to ensure its stability. The above is an introduction to the design method of bare board power module, and I hope it will be helpful to you.
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Product selection and application considerations
The design power of each product of our company will have a certain amount of redundant power, which can run for a long time under full load or even over the rated load. However, for the sake of high reliability and prolonging the service life of the power supply, please do not let the load reach the rated value. It is generally recommended to use 60%-80% of the rated load, and the ambient temperature is recommended to be about 30 ℃, which can be fully loaded at an ambient temperature of 55 ℃, but this will undoubtedly greatly reduce the reliability and service life of the product. In actual use, please pay attention to the two factors of controlling load and temperature. If the ambient temperature is relatively high, it is necessary to reduce the load as much as possible (that is, to increase the load margin and select products with greater output power). On the contrary, if a large load current is required, then try to do a good job of ventilation and heat dissipation, such as placing the power supply module in an open space and increasing cooling fans. The specific value is not absolutely fixed. Generally, it is recommended that the load should not exceed 20% of the rated load when the ambient temperature is 55 ℃, which can keep the product very high reliability. Tip: Please use temperature measuring equipment to evaluate the temperature, and do not rely on skin feeling. Short time and a small proportion of full load, high temperature operation, the reliability and life has little effect. For example: each full load lasts less than 1 minute or half a minute, and the interval is more than 10 minutes, while the load during the interval is less than 15% of the rated load, then even if the operation at 55 ℃ is also possible. Safe Use Warning: Since the bare board series does not have a shell, the input is 220V AC at the same time. The input pins and corresponding terminals of the module are directly connected to 220V. Please pay great attention to prevent short circuit between electric shock and metal objects and ensure that the power supply is disconnected before any touch. Load Requirements for 2. Use of Multiple Output Power Supplies Generally, the voltage accuracy of the output of the multi-output power supply is: the nominal value of the main output is plus or minus 1%, and the nominal value of the secondary output is plus or minus 5%-10%. The first output of the multi-output power supply is the main circuit, and the other output is the secondary circuit. The voltage accuracy and carrying capacity of the main circuit are higher than those of the secondary circuit. Therefore, the main circuit with large current and high voltage accuracy requirements should be generally selected, it is appropriate that the ratio of each current is 50-100%, and the secondary circuit must not be loaded separately under the condition of no load on the main circuit, otherwise the secondary circuit voltage is too low to be used normally. In addition, if the main circuit load is full load and the secondary circuit load is light load, the secondary circuit voltage may increase, otherwise the secondary circuit voltage will decrease, and the reliability and service life will have little effect. For example, if each full load lasts less than 1 minute or half a minute, and the interval is more than 10 minutes, while the load during the interval is less than 15% of the rated load, then even operation at 55°C is possible.
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