Detailed explanation of the circuit principle of the inductive DC-DC converter

One-piece inductor

As shown in Figure 1, a simplified inductive DC-DC converter circuit that closes the switch causes an increase in current through the inductor. Turning on the switch causes current to flow through the diode to the output capacitor. Since the current from the inductor is stored, the voltage of the output capacitor rises after a plurality of switching cycles, and as a result, the output voltage is higher than the input voltage.

What are the factors that determine the output voltage of an inductive boost DC-DC converter?
In the actual circuit shown in Figure 2, an IC with an integrated power MOSFET replaces the mechanical switch, and the MOSFET is turned on and off by a pulse width modulation (PWM) circuit. The output voltage is always determined by the PWM duty cycle. At 50% duty cycle, the output voltage is twice the input voltage. Double the voltage will make the input current reach twice the output current. For the actual lossy circuit, the input current is slightly higher.

How does the inductance value affect the performance of an inductive boost converter?
Since the inductor value affects the input and output ripple voltage and current, the choice of inductor is the key to the design of the inductive voltage converter. An inductor with a low equivalent series resistance has the best power conversion efficiency. The inductor saturation current rating is chosen to be greater than the steady state inductor current peak of the circuit.

What is the principle of the output diode selection of the inductive boost converter IC circuit?
The boost converter is a fast Schottky rectifier diode. Compared to conventional diodes, Schottky diodes have a low forward voltage drop, making them low power and high efficiency. The average current rating of the Schottky diode should be greater than the maximum output voltage of the circuit.



How to choose the input capacitance of the inductive boost converter IC circuit?
The input to the boost regulator is a triangular voltage waveform, so the input capacitor must be required to reduce input ripple and noise. The amplitude of the ripple is inversely proportional to the magnitude of the input capacitance, that is, the larger the capacitance, the smaller the ripple. If the converter load changes little and the output current is small, it is safe to use a small input capacitor. If the converter input is very small from the source output, a small volume capacitor can also be selected. If the circuit is required to have little interference to the input voltage source ripple, a large capacitance may be required and (or) the equivalent series resistance (ESR) may be reduced.

What factors should be considered when selecting an output capacitor in an inductive boost converter IC circuit?
The choice of output capacitor is determined by the output voltage ripple. In most cases, low ESR capacitors such as ceramic and polymer electrolytic capacitors are used. If you use a high ESR capacitor, you need to look carefully at the converter frequency compensation and you may need to add an extra capacitor to the output circuit.



What factors need to be considered when making an inductive boost converter IC circuit layout?
First, the input capacitor should be as close as possible to the IC, which reduces the copper trace resistance that affects the IC input voltage ripple. Second, place the output capacitor near the IC. The copper trace length connecting the output capacitors affects the output voltage ripple. The third point is to minimize the trace length of the connected inductor and output diode, reducing power consumption and improving efficiency. Finally, the output feedback resistor is far from the inductor to minimize the effects of noise.

Where are the inductive boost converters used?
One of the main application areas for inductive boost converters is to power white LEDs that provide backlighting for liquid crystal display (LCD) panels in battery-powered systems. It can also be used in general purpose DC-DC voltage regulators that require a boost voltage.