STMicroelectronics STLDC08 Demo Board STEVAL-ILL039V1/2 STEVAL-ILL039V1 STEVAL-ILL039V1 Fiche De Données

Doc ID 18476 Rev 1

21/29

Schottky diodes, with their low forward voltage and fast recovery time, are the ideal choice to 
maximize efficiency. The output diode in a boost converter conducts current only when the 
power switch is OFF. The average current is equal to the output current and the peak current 
is equal to the peak inductor current. Ensure that the diode's average and peak current 
ratings exceed the average and peak inductor current, respectively. In addition, the diode's 
reverse breakdown voltage must exceed the regulator output voltage.

The input capacitor of a boost converter is less critical than the output capacitor, due to the 
fact that the input current waveform is continuous. The input voltage source impedance 
determines the size of the input capacitor, which is typically in the range of 10 µF to 100 µF. 
A low ESR capacitor is recommended though it is not as critical as the output capacitor.

For best output voltage filtering, a low ESR output capacitor is recommended. Ceramic 
capacitors have a low ESR value but tantalum capacitors can be used as well, depending on 
the application.

The output voltage ripple consists of two parts, the first is the product I

L(PK)

 ESR, the second 

is caused by the charging and discharging process of the output capacitor.

where:

I

L(PK)

 = Peak current 

I

LED

 = Load current

C

OUT

 = Selected output capacitor

ESR = Output capacitor ESR value

)

PK

(

L

OUT

LED

OUT

I

ESR

C

I

TON

V

×

+

×

=

Δ