With a switch-mode power supply (SMPS) each component has to be carefully selected to optimize the efficiency of the system and to ensure that the correct voltage well as the power levels that are required of the specific application.
Even with DC input and DC output through a system, the use of an SMPS inductor is a critical consideration. Finding the right DC-DC power conversion system through a carefully selected inductor will keep the system running efficiently and within all power specifications required.
The Need for SPMS
As mentioned, the DC-DC power conversion is part of the SMPS system. The reason switch-mode power supplies are so frequently used with sensitive equipment such as microprocessors and LEDs is the voltage drop that can occur with batteries as they discharge. Without the use of the SMPS inductor these changes in voltage, either too high with a full charge or too low when discharging, would impact the functioning of the system.
As the SPMS energy storage component, the inductor is able to ramp up the power internally when the switch is on. In essence, this ramping up is like charging the inductor so that when the switch cycles off this stored energy can be released to balance the output.
The goal in choosing the correct SMPS inductor is to maintain the desired consistent voltage out while also limiting any type of voltage ripple when the inductor is discharging.
In some types of systems, most notably with a buck converter, the use of AC and DC power into the inductor is critical. The AC will flow through the capacitor and create a ripple voltage. The choice of the capacitor to allow for this ripple current rating should be at about 30% of the maximum load current.
By choosing this option, you will also need to choose an inductor that is able to provide a continuous output current of about 15% of the full load. In this balance, the capacitor and the inductor work together through the duty cycle to maintain all required levels of current throughout the system. In addition, you will need to know the duty cycle, the switching frequency, the maximum input voltage as we as the output voltage.
Selecting the right inductor and capacitor for the switch-mode power supply is important to ensure efficiency, which can be up to 90% will a system that is carefully designed and customized.