Derivation of duty cycle D, inductance L and efficiency η of switching power supply

SMPS (switched mode power supply) is a very efficient power converter, its theoretical value is close to 100%, there are many kinds. According to the topological structure, there are boost, buck, boost buck, charge pump, etc.; according to the switch control mode, there are PWM, PFM; according to the switch tube category, there are BJT, FET, IGBT, etc. This discussion focuses on the commonly used PWM control buck and boost types of data card power management. The main components of switching power supply include: input source, switch tube, energy storage inductor, control circuit, diode, load and output capacitance. At present, most semiconductor manufacturers will integrate switches, control circuits and diodes into a CMOS / bipolar process power management IC, greatly simplifying the external circuit. As a key device of switching power supply, energy storage inductor plays an important role in the performance of power supply, and it is also the focus of product design engineers and debugging objects. With the development of consumer electronic devices such as mobile phones, PMP and data cards, their sizes are moving towards the trend of light, thin, compact and fashionable, which is in contradiction with the larger capacity and larger size of inductors and capacitors required by the stronger product performance. Therefore, how to reduce the size of the inductance (occupied PCB area and height) of the switching power supply under the premise of ensuring the product performance is an important proposition to be discussed in this paper. The designer will have to trade off the circuit performance and inductance parameters. Everything has two sides, switching power supply is no exception. Bad PCB layout and wiring design will not only reduce the performance of switching power supply, but also strengthen EMC, EMI, ground spring, etc.