Inductance selection and calculation of DC-DC circuit
Time:2024-04-27
Views:148
Inductance is an important part of the power supply circuit, and the position of the inductance can help us lock the position of the power supply part at a glance in the complex circuit. This article will analyze how to choose the appropriate inductor and its parameters in the DCDC circuit. Welcome corrections and additions.
1. Classification of inductors
The inductors commonly used in DC-DC circuits can be roughly divided into the following two types:
2. Function of inductance in power supply
Taking the basic buck circuit as an example (the subsequent calculations are based on the buck circuit), the inductor plays the following two main roles in the circuit:
(a) Energy storage: As an energy storage component, when Q1 is turned on, L and Cout store energy to ensure the power supply when Q1 is turned off and Q2 is turned on, forming a continuous current loop.
(b) Smooth output current: Due to the characteristics of inductors that hinder current changes, L and Cout constitute a second-order filtering system to smooth the output current.
3. Calculation of inductance value
According to the relationship between the voltage and current at both ends of the inductor, it can be deduced as follows:
As can be seen from the above formula, the size of inductance will affect the ripple size of output current, and increasing the inductance value can reduce the current ripple. Usually, expect
Therefore, by bringing in the maximum on-load current and the maximum input voltage, the minimum inductance value can be derived backwards.
4. Consider other inductance parameters
In addition to considering the inductance value, it is also necessary to pay attention to the saturation current and DCR of the inductance. After the inductance is saturated, its permeability u will greatly decrease, resulting in a decrease in inductance, and finally the inductance loses the ability to inhibit current mutation. After saturation, the inductance current waveform will appear obvious distortion, abnormal temperature rise or obvious whistling phenomenon.
Through the inductance waveform can be obtained the inductance to withstand the peak current formula:
The specification of the finished inductor will mark its saturation current, and pay attention to the selection of inductors whose saturation current is greater than IL_peak.
DCR (Direct Current Resistance) refers to the direct current resistance of the inductor, for the same size of the inductor, the DC resistance usually presents the following characteristics: if the inductor value is higher, the direct current resistance value is higher; If the inductance value is low, the DC resistance value is low. The size of DCR is closely related to the heating loss of the inductor, so the DCR is generally expected to be as small as possible when selecting the inductor to improve efficiency.
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