The main basis for selecting the inductor of the Buck converter is the magnitude of the converter output current. Assume that the maximum rated output current of the Buck converter is maxoI and the minimum rated output current is minoI. When the output current of the Buck converter is equal to maxoI, it is still necessary to ensure that the inductor operates in an unsaturated state so that the inductance value can be kept constant. A constant value of 1L in inductance ensures a linear rise and fall in the current across the inductor. Secondly, the minimum rated output current minoI and the inductance value 1L determine whether the operating state of the Buck converter will enter the DCM mode. We know that when the Buck variator works in CCM mode, And when the output voltage OV, the input voltage dcV and the duty cycle T of the converter are constant, the on-time Ton remains unchanged. According to the critical conditions of CCM mode and DCM mode, the minimum output current of CCM mode is The critical inductance value of the CCM mode and DCM mode of the simultaneous converter of the triple converter The selection of the output capacitance of the Buck converter is closely related to the magnitude of the ripple voltage. We know that the actual capacitor C1 can be equivalent to the circuit structure as shown. The resistor R0 is an equivalent series resistance (ESR), and the inductor L0 is an equivalent series inductance (ESL). When the frequency is lower than 300KHz or 500KHz, the equivalent series inductance of the capacitor C1 can be neglected, and the output ripple voltage mainly depends on the capacitor C0 and the equivalent series resistance R0. The equivalent circuit of capacitor C1 and the current and voltage changes on capacitor C1 As can be seen from the above figure, the current on capacitor C1 is Therefore, the maximum variation of the current on the capacitor C1 is 1Liï„, so the peak value of the voltage fluctuation generated on the equivalent series resistor R0 is The peak value of the voltage ripple on capacitor C0 is Therefore, the voltage ripple ppV on the output voltage OV is However, from some manufacturers' product manuals, most commonly used aluminum electrolytic capacitors 00*RC are a constant and equal to 50~80*10^-6F-~. The operating frequency of the Buck converter is generally 20 to 50 KHz, so the period is 20 to 50 * 10 ^ -6 S. therefore, Therefore, in general, we can ignore the ripple voltage generated by capacitor C0, then the voltage ripple ppV is approximately The voltage ripple and inductor current variation can be obtained from the system parameters, so the value of the variable 0R can be found. Then, the common aluminum electrolytic capacitor 00*RC is a constant to calculate the capacitance value 0C that the system should use. Customized Laboratory Testing Instruments Wuxi Lerin New Energy Technology Co.,Ltd. , https://www.lerin-tech.com
How to choose the filter capacitor inductance of buck converter and its usage
Buck converter inductance selection