AN2495 datasheet(12/36 Pages) STMICROELECTRONICS

Part #	AN2495

Description	The purpose of this application note is to explain the design

PDF	36 Pages

Scroll/Zoom	100%

Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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12 / 36 page

Flyback stage design

AN2495

12/36

Doc ID 13127 Rev 5

For practical considerations, to better optimize the utilization of the transformer window, and

comply with Equation 15 to Equation 18 and Table 2, it can be determined that:

Equation 19

The specifications of the transformer according to the above calculations are listed below.

Application specifications

Safety information - IEC EN60950

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Vinmin = 250 V DC

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Vinmax = 850 V DC

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Poutmax = 80 W

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Vout = 24 V (power output 80 W)

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Ioutmax = 3.33 A

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Vaux = 15 V (to drive the IC < 1 W)

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Fswmin = 50 kHz (max. load, min. Vin)

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Vflyback = 250 V

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Ipeak(primary) = 1.6 A

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Irms(primary) = 0.65 A

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Ipeak(secondary) = 16 A

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Irms(secondary) = 6.5 A

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Lp (primary inductance) = 1.56 mH

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Np/Ns = 10

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Np/Naux = 17

Wires and ferrite used

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Np = 120 d = 0.28 mm

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Ns = 12 d = 0.5 mm 3 in parallel

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Naux = 7 d = 0.28 or smaller

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The core used is an ETD 34, N67 material from EPCOS or equivalent.

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Air gap = 1.8 mm

0.05 cm

[]3inparallel

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