Design and Analysis of AC-DC Power Supply Module
Release time:
2022-08-26 11:16
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AC-DCPower supply moduleIt refers to the converter that converts alternating current into direct current. The connection mode is divided into half-wave and full-wave circuits. It is divided into single-phase, three-phase and multi-phase according to the number of phases. The power flow direction can be bidirectional. now introduce85 ~ 265 VAC,50HzInputAC-DCPower supply moduleThe design converts alternating currentDCThe simple method is a rectifier bridge rectifier.50HzAC power is converted into pulsation after full-wave rectificationDCThe voltage is then obtained through the input filter capacitor.DC.

1The choice of rectifier bridge. The main parameter of the rectifier bridge is the reverse peak voltageVRRAverage rectified currentIF, forward voltage dropVFReverse leakage currentIRMand peak forward surge currentIFSM. Reverse breakdown voltage of rectifier bridgeVRMshall satisfyVRM.
2Selection of input filter capacitor. Rated voltage of aluminum electrolytic capacitor(1.3Times)As the surge voltage of the capacitor, when the working voltage is higher160Vrated working voltage50VAs a surge voltage, the manufacturer allows to withstand this voltage in a short time. Capacitor in the surge voltage, the current is large, a long time will explode. Therefore, aluminum capacitors should have a higher rated voltage, and the actual working voltage should be the standard rated voltage.70~80%.
3Design of power transformer. Considering the small output power and volume constraints, a small ferrite core is selected to complete the power conversion.
4, output rectification and filtering. Since the output voltage isDC 5V, The low-voltage square wave transformed by the transformer needs to be rectifiedDCand then use aluminum electrolytic capacitor energy storage filter. The operating frequency of the rectifier is equal to the switching frequency of the power switch tube, so the output rectifier diode should be a Schottky rectifier diode with fast recovery function, and the standard current value of the output rectifier diode(IF)should be the outputDCMore than three times the current rating. The AC resistance of aluminum electrolysis for rectification should be low and the capacitor capacity should be large, otherwise the high frequency AC current in the current cannot be filtered out, and the package volume should not be too large. If the standard value is selected, it is330F/10Vof aluminum electrolytic capacitors., You need to add one to the output of the power supply.LCFilter unit, in order to reduce the output rippleLTake10μHФ around4*7The small I-shaped inductance,CTake100μF/10VAluminum electrolytic capacitor.
5Control feedback unit. Feedback circuit using voltage referenceTL431and optocouplersP521As a combination of reference, isolation and sampling, it can control the change of output voltage.1%Within. The feedback voltage is sampled by the output terminal, and the output voltageV0by voltage dividing resistanceR63andR64Sampling, andTL431in2.5VThe reference voltage is compared and the error voltage is output. Change by optocouplerVIPer12AChip control terminal currentIFBand then by changingPWMwidth to adjust the output voltageV0to keep it unchanged.
AC-DCPower supply moduleThe design is not only based on the characteristics of small size, low power consumption, light weight, reliability, electromagnetic compatibility and high efficiency, but also from the development of electronic equipment.
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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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