NCP1015公司AND8226-D

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© Semiconductor Components Industries, LLC, 2005October, 2005 − Rev. 11Publication Order Number:

AND8226/D

AND8226/DNonisolated Positive OutputBuck AC/DC Converter

Prepared by: Jan GrulichON Semiconductor

This application note describes the way, how to easilydesign the simple, non isolated AC/DC converter forpowering low voltage control part of mains applicationswith triac, or SCR power switch. Some examples are:dishwashers, microwave ovens, coffee machines, nightillumination and so on. In comparison with resistive, orcapacitive dropper is this solution more comfortable andfeatures some advantages such as:•Wide Input Voltage Range 85 VAC – 265 VAC

•Smaller Size, Lower Weight, Lower Total Cost

•Good Line and Load Regulation, No Need of

Additional Linear Regulators•Efficient Design with Up to 80% Efficiency

•Overload, Short−Circuit and Thermal Protected

•Simple for Low Cost Mass Production

•Universal Design for Wide Range of Output Currents

and Voltages

The monolithic power switcher, used in this application,greatly simplifies the total design and reduces time toproduction. The new line of the Power Switchers, NCP1010through NCP1014, is ideal for this purpose. This IC in theSOT−223 package reduces size and is suitable for massproduction. The design consists of input filter, rectifier withfiltering capacitor, power stage with switcher and inductor,output ultrafast rectifier, output filtering capacitor, feedbackloop with zener diode and optocoupler and indicating LED.The only component necessary for proper powering of theIC is the VCC capacitor. The IC is directly powered from theHV Drain circuit via internal voltage regulator. To eliminatethe noise at the feedback input, some small ceramiccapacitor with value of around 1.0 nF is necessary to beconnected as close to the FB pin, as possible.

Schematic diagram

Figure 1. Complete Schematic Diagram of the 12 V/0.2 A ConverterD1MUR160

D21N4007

L21 mH

C1100 nFR11kCON2ARK750/2CON2ARK500/2C21 nFL11.5 mHIO1PC817E2220 mF/25 V

E347 mF/25 V

E110 mF/400 V

VCC

GNDFB

HV

IO2NCP1014STZD1

11 V

LD1GRN

121

2

++

+

APPLICATION NOTEhttp://onsemi.comAND8226/D

http://onsemi.com2

SELECTION OF CRITICAL COMPONENTSInductor selectionFor the selected output power need to be selected certainminimum value of the inductance. This value is dependenton the mode of operation. Reduced value results inDiscontinuous Conduction Mode of operation (DCM).Practically was found, that the borderline betweenContinuous Conduction Mode of operation (CCM) andDCM is commonly set slightly below maximum outputpower. The result is low cost of the inductor, freewheelingdiode (trr > 35 ns), higher efficiency and lower cost. Thenegative result is in lower output power and higher cost ofthe NCP101x Power Switcher.The current ripple in the inductor during the Ton time maybe expressed by Equation 1.

DIripple(Ton)+Ton@ǒ(Vmin*Vds*VO)LminǓ(eq. 1)

Where:Ton = ON Time, Internal Power Switch in ON,Vmin = Minimum Rectified Input Voltage,Vds = Drain−to−Source Voltage Drop,Vo = Output Voltage,Lmin = Minimum Inductor Value.The current ripple in the inductor during the Toff time maybe expressed by Equation 2.

DIripple(Toff)+Toff@ǒVOLminǓ(eq. 2)

Toff = OFF Time, Internal Power Switch in OFF.The current through the inductor at the beginning of theTon time is shown by Equation 3.

Iinit+Iset*DIripple(eq. 3)

Iset = Peak Switching Current Set by the FB Loop.

The average current through the inductor over oneswitching cycle can be expressed by Equation 4.

Ic+fop_min@ǒǒDIripple2)IinitǓ@Ton)ǒDIripple2)IinitǓ@Toff

Ǔ(eq. 4)

Ic = Inductor Operating Current,fop_min = Minimum Operating FrequencyThe theoretical minimum inductor value corresponds toEquation 5.

Lmin+

(2@VO@IO@(Vmin*Vds*VO))

(DIripple2@fop_min@(Vmin*Vds))(eq. 5)

IO = Output DC Current.The theoretical maximum output power will be shown inEquation 6.

@ǒ(Vmin*Vds)(Vmin*Vds*VO)Ǔ2(eq. 6)

Pout_max+Lmin@(Iset

2*Iinit2)@f

op_min

The current ripple in the inductor during the normaloperation will be shown in Equation 7.

DIripple+((Vmin*Vds*VO)@VO)((Vmin*Vds)@fop_min@Lmin)(eq. 7)

The output current will be shown in Equation 8.IO+fop_min@

((Iset)Iinit)@Ton)(Iset)Iinit)@Toff)

2(eq. 8)

Table of Preselected Inductors (Vmin = 120 V, Vds = 9 V, VO = 12 V, Iset = 0.405 A, fop_min = 59 kHz)

Inductance(mH)Coilcraft Part Number (see appendix for address)DIripple(A)Output Current(A)

470RFB0810−4710.390.25680RFB0810−6810.270.32820RFB0810−8210.220.341000RFB0810−1020.180.361500RFB0810−1520.120.40NOTE:The output current is the theoretical value and need to be multiplied by the efficiency (~0.7).