AN4501 datasheet(17/48 Pages) STMICROELECTRONICS

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AN4501

Selection of the inductor

The selection of the inductor in a DC-DC converter has a direct influence on the

performance and the selection of the other power devices. Therefore, care must be taken

for its choice, as it dictates the cost and the overall performance of the system.

Like the switching frequency, the choice of the inductance value is a tradeoff between its

size, its cost and the inductor current ripple.

A larger inductance results in:

•

Smaller inductance current ripples

•

Smaller input voltage and current ripples

•

Smaller output voltage and current ripples

•

Smaller current peaks in the converter switching MOSFET

•

Smaller diode peak currents

However, a larger inductance value means higher cost, larger PCB surface and in general

slower response time to transients.

Figure 6. Inductor waveforms of a boost converter in CCM

4.1

Converter Duty cycle

The expression of the ideal duty cycle of a boost converter, without power losses is:

Equation 1:

The effective duty cycle taking into account the different sources of power losses is:

ideal

OUT

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AN4501 Datasheet(PDF) 17 Page - STMicroelectronics