Fujitsu MB39A104 manual Di ≥ I O ⋅ 1

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 : IDi

IDi ≥ IO ⋅ (1 − VO )

VIN

Diode peak current : IDip

IDip ≥ (IO + VO toff) 2L

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
IDi ≥ IO ⋅ (1 −	VO	)
	VIN

≥3 ⋅ (1 − 0.263)

≥2.21 A

CH2
IDi ≥ IO ⋅ (1 −	VO	)
	VIN

≥3 ⋅ (1 − 0.174)

≥2.48 A

CH1
IDip ≥ (IO +	VO	toff)
	2L

≥3.24 A

CH2
IDip ≥ (IO +	VO	toff)
	2L

≥3.18 A

29