What factors should be taken into account in the selection of a switch mode power supply?
Below we talk about the power supply mall, other than the primary switching power supply topology structure. Flyback power supply output voltage transient control characteristics are better, the load capacity is stronger, but its shortcomings are also significant, more than one large energy storage filter inductor and a current diode, large volume, transformer primary coil reaction potential voltage is high, the switching tube of the central requirements of the higher (briefly breakdown damage). Push-pull power supply current transient care speed is very high, voltage output characteristics are very good, in all topologies, is the highest rate of use of a switching power supply, no magnetic leakage, drive circuit is simple. But its disadvantage is that the two switching devices need a very high withstand voltage value; to have two sets of primary coils, on the small power output push-pull switching power supply is a disadvantage. If the two forward converter is not completely symmetrical or balanced, after a few cycles of accumulated bias magnetism, will make the core into the fullness, resulting in high-frequency transformer excitation current is too large, and even damage to the switching tube. Bridge switching power supply output power is very large, high operating power, the switching tube voltage withstand value of the central demand is relatively low, the transformer primary coil only needs a winding. The disadvantage is that the power is low, it will present a semi-conducting region, and the loss is large.
In addition to the topology structure selection time to think about its advantages and disadvantages, we also need to determine the load based on the status of resolute, some loads are more stable, some loads are not resolute larger, and even some will have no load, or full load, or a moment of the load becomes large, or a moment of the load down the situation occurs, if there is this kind of question, the best with the power supply module manufacturers to clarify the recognition of its programme has been the necessary response to the protective Programme approach, not all power supplies are able to achieve this policy. Therefore, the type of load is also an influential factor. Usually the module, its output is in accordance with the default for the resistive load and the programme, assuming that the load is rational or capacitive loads, need to be clarified with the module manufacturers alone in order to factory power module internal equipment or parameters slightly adjusted.
In addition to the above very primary selection elements, we also need to think about the switching frequency, ripple, safety requirements of the switching power module selection. The switching frequency of the power supply module is also need to pay attention to, he picked the external power supply filter filter parameters (cut-off frequency, order) of the selection. Ripple and topology, capacitance and inductance parameters, load conditions are related to a 5v power supply, ripple to do 50mv, a single power supply error that is 1%, for the high precision requirements of the circuit, power supply errors, errors in the widening circuit, signal cable errors, AD rounding errors, more than one error after the accumulation of the merger, the total error can be a big one. Power module with or without filtering scheme, power module address equipment with or without safety requirements (leakage current, insulation voltage, humidity requirements), temperature characteristics, change power, the input voltage is not resolute scheme, load adjustment rate, etc., the central requirements of the local is still quite a lot. So we can understand the selection of switching power supply module, not only the cost of the only policy worthy of attention.
