© Semiconductor Components Industries, LLC, 2003

February, 2003 - Rev. 2

1

Publication Order Number:

AND8099/D

AND8099/D

5.0 V, 2.0 A Flyback

Converter

Prepared by: Kristie Valdez

ON Semiconductor

The design of a switching power supply is an iterative

process which involves many variables that have to be

adjusted in order to obtain an optimized solution. However,

there are trade-offs which allow for a simple low cost, low

component, single sided board design method. This

application note provides a simple approach to designing

a converter utilizing the ON Semiconductor NCP1055

high

voltage

switch

regulator.

The

easy-to-follow

step-by-step procedure guides the user into designing the

different blocks that constitute the power supply, mainly the

input block, the power stage, the magnetics, the snubber, the

output block, and the feedback loop. The circuit diagram,

bill of material, and PCB layout are also included at the end

of the application note. This power supply is specifically

designed for a 5.0 V, 2.0 A output and a maximum duty cycle

of 48%. It meets IEC and UL requirements. EMI is minimal

and a 70% achievable efficiency or greater is possible.

The NCP1055 is a family of monolithic high voltage

switching regulators designed to work in rectified AC line

sources and flyback converter applications. They are

capable of providing an output power ranging from 6.0 W to

40 W with a fixed AC input of 100 V, 115 V, or 230 V

and 3.0 W to 20 W with a variable AC input ranging from

85 V to 265 V. This device features an on-chip 700 V

SENSEFET

™ power switch circuit, an active startup

regulator circuit which eliminates the need for an auxiliary

bias winding on the converter transformer, fault logic with

a programmable timer for converter overload protection.

Protective features provide power switch current limiting,

input under voltage lockout with hysteresis, thermal

shutdown, and restart fault detection. For more information,

please contact an ON Semiconductor sales representative or

log on to www.onsemi.com.

Design Parameters

The first step in designing a power supply is to define and

predetermine the input and output parameters.

Universal Input Voltage Range:

Vin(min) + 85 VAC, Vin(max) + 265 VAC

Output Specifications:

Vout + 5.0 V " 2%, Iout + 2A

Input Power:

Pin +

Pout

est.eff

,

an efficiency of 0.78 is a good starting

point for a flyback converter using

MOSFET technology:

Pout + 5·2.0 + 10 W

NPin + 10

0.78

+ 12.82 W

DC Rail Voltages at Low Line and High Line:

Vpeak(min) + Vin(min) ·2 + 85 · 2 + 120.21 VDC

Vpeak(max) + Vin(max) ·2 + 265 · 2 + 374.77 VDC

Average Input Current at Low Line:

Iin(avg) +

Pin

Vin(low)

,

where Vin(low) + Vpeak(min) * Vripple * Vdiode;

Iin(avg) +

12.82

80.2

+ 0.160 A

Vripple + 32% Vpeak(min)

Input Peak Current:

Ipeak + 2·Iin(avg) ·

tsw

ton

Ipeak + 2 · 0.160 ·

10

ms

4.8

ms +

0.667 A

APPLICATION NOTE

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