Fujitsu MB39A104 Manual do Utilizador descarregar pdf (Página 29)

MB39A104

• Flyback diode

The flyback diode is generally used as a Shottky barrier diode (SBD) when the reverse voltage to the diode is

less than 40V. The SBD has the characteristics of higher speed in terms of faster reverse recovery time, and

lower forward voltage, and is ideal for achieving high efficiency. As long as the DC reverse voltage is sufficiently

higher than the input voltage, the average current flowing through the diode is within the average output current

level, and peak current is within peak surge current limits, there is no problem. In this application the Rohm

RB053L-30 is used. The diode average current and diode peak current can be calculated by the following

formulas.

Diode mean current : I

Diode peak current : IDip

Example: Using the Rohm RB053L-30

VR (DC reverse voltage) = 30 V, average output voltage = 3.0 A, peak surge current = 70 A,

VF (forward voltage) = 0.42 V, IF = 3.0 A

CH1

CH2

CH1

CH2

Di ≥ IO × (1 −

)

VIN

IDip ≥ (IO +

toff)

Di ≥ IO × (1 −

)

VIN

≥ 3 × (1 − 0.263)

≥ 2.21 A

IDi ≥ IO × (1 −

)

VIN

≥ 3 × (1 − 0.174)

≥ 2.48 A

IDip ≥ (IO +

toff)

≥ 3.24 A

IDip ≥ (IO +

toff)

≥ 3.18 A

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Fujitsu MB39A104 Manual do Utilizador Página 29