Many engineers who have not used switching power supply design will have certain fears, such as concerns about switching power supply interference, PCBlayout problems, component parameters and type selection issues. In fact, as long as you understand, using a switching power supply design is very convenient.
A switching power supply generally consists of a switching power supply controller and an output. Some controllers integrate the MOSFET into the chip, which makes it easier to use and simplifies PCB design, but the design flexibility is reduced.
The switch controller is basically a closed-loop feedback control system, so there is generally a sampling circuit that feeds back the output voltage and a control circuit for the feedback loop. Therefore, this part of the design is to ensure accurate sampling circuit, and to control the feedback depth, because if the feedback loop response is too slow, there will be a lot of impact on the transient response capability.
The output part design includes output capacitors, output inductors, MOSFETs, etc. These choices are basically to balance a performance and cost, such as high switching frequency can use small inductance values ​​(meaning small package and Cheaper cost), but high switching frequency increases interference and switching losses to the MOSFET, resulting in reduced efficiency. The result of using a low switching frequency is the opposite.
The ESR of the output capacitor and the Rds_on parameter selection of the MOSFET are also critical. A small ESR can reduce the output ripple, but the cost of the capacitor will increase, and a good capacitor will be expensive. Switching power supply controller drive capability should also be noted that too many MOSFETs cannot be driven well.
In general, the supplier of the switching power supply controller will provide specific calculation formulas and usage plans for engineers to learn from.
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