INTRODUCTION goal this paper present design example rated AC-DC adapte

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INTRODUCTION goal this paper present design example rated AC-DC adapte

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AND8128/D Cost AC-DC Adapter with NCP1215
INTRODUCTION goal this paper present design example rated AC-DC adapter consumer products like mobile phone, walkman, walkie-talkie, MPEG players, digital camera, various battery chargers, etc. This sort adapter specified very cost hamper selling price above products. However, this does imply that adapter designer sacrifice safety, precision standby performance. implementing NCP1215 dedicated switched-mode power supply (SMPS) control build adapter that meet those requirements. This achieved with help following NCP1215 basic features: Current Mode Control: Cycle-by-cycle primary current observation helping prevent significant primary overcurrent which would cause transformer's core saturation consequent serious power supply failure. Negative Primary Current Sensing: Negative current sensing offers elegant drive MOSFET without reducing available gate-source voltage sense resistor voltage grows-up deteriorating voltage image primary current strong turn-on pulse input capacitance. programming resistor offers another degree freedom when selecting voltage across sense resistor. Furthermore, programming resistor together with capacitance forms low-pass filter which cleans residual noise generated main switch turn-on charging process parasitic capacitances included transformer's windings, snubbers, output diode, printed circuit board traces. Very Start-up Current: patented internal supply block specially designed offer very current consumption during start-up. allows very high value external start-up resistor, greatly reducing dissipation, efficiency standby power consumption.
Frequency Foldback: Since switch-off time
increases when power demand decreases, switching frequency naturally diminishes light load conditions. This helps minimize switching losses offers excellent standby power performance. Secondary Primary Regulation: feedback loop arrangement allows secondary primary side regulation without significant additional external components. exploitation above-mentioned features build AC-DC adapter with NCP1215 quite efficient way. Since operation NCP1215 differs significantly from standard fixed frequency current mode controllers, more detailed explanation operation will follow. Summary NCP1215 Operation There identified basic categories power losses within SMPS. These conduction switching losses. conduction losses become dominant rather high output power levels. situation completely change when demanded output power decreases standby level. this situation, switching losses become major contributor power leak. This situation typical standard control IC's working with fixed switching frequency. even worse SMPS based very popular self-oscillating concept where light load condition switching frequency usually escalates very high values. idea behind NCP1215 operation reduce switching losses SMPS during this light load standby operation. This simply ensured keeping constant primary time. result, output regulation obtained adjusting time duration. This exactly NCP1215 working. Experimental results have proven concept with excellent standby consumption no-load conditions.
Semiconductor Components Industries, LLC, 2003
September, 2003 Rev.
Publication Order Number: AND8128/D
AND8128/D
switching frequency decreases output power demand goes down, will move opposite direction when responding output increase. light load conditions, frequency really operation within audible range feasible. Since peak primary current maximum working range, power pulses audio frequency induce audible whistle coming mainly from transformer. power supply user does appreciate this whistle. solution compromise between those extremes. result control apparatus that light load condition fixed peak primary current certain portion maximum value. This little current reduction helps away from audio range lower level audio noise. increases standby self-consumption, significantly. higher output power levels peak primary current continuously increases maximum. resulting block diagram internal structure seen Figure From that figure basic element idea described above current source connected pin. value varies between 12.5 depending signal coming from feedback block. resulting transfer characteristic seen Figure
Feedback Loop Control
Iref Off-Time Comparator Reference Regulator
Voffset
12/8.5
Undervoltage Lockout
12.5-50
Gate Driver Gate
Current Sense Comparator Reset
Figure Representative Block Diagram
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AND8128/D
Source Current
POUT Goes Down Voltage POUT Goes Voffset Sink Current toff-min
12.5
Figure Current Sense Regulation Characteristic
Figure Voltage (Pout1 Pout2 Pout3)
variable current source dictates through external resistors peak primary current. time generated timer consisting time comparator, current source, discharge switch external timing capacitor. signal that observed shape depicted Figure
Line
this shape allow time several seconds even stop switching. This basic summary operation. practical design AC-DC adapter will follow.
LL4148 P6SMB200AT3 MURA160T3 Gate
nF/Y
S250 Neutral
MBRS360T3
+6.5
mF/25 BC846B BZX55C5V6
NCP1215
IRFRC20 ISO1
SFH6156
Figure Schematic Diagram AC/DC Adapter with NCP1215
AC-DC Adapter Board adapter depicted Figure maximum performance ratings:
Output Voltage Output Current Min. Input Voltage Max. Input Voltage Max. Switching Frequency
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AND8128/D
Using specification input voltage bulk capacitor voltage range calculated follows:
Vbulk- VAC- Vbulk- VAC-
adapter output voltage number turns secondary winding calculated accounting Schottky diode output rectifier follows:
Vfwd)(1 max)np Vbulk-
power conversion efficiency this size adapter would appropriate. input power then estimated follows:
outh
(6.5 0.5)(1 0.5)150 8.26 turns
average value input current minimum input voltage
Iin-avg 51.2 Vbulk-
Using calculated number secondary winding turns number turns auxiliary winding calculated:
naux (Vaux Vfwd) Vfwd
suitable reflected primary winding voltage rated MOSFET switch
Vflbk Vbulk- Vspike
(14.5 17.7 turns
Using calculated flyback voltage maximum duty cycle calculated:
Vflbk 0.496 Vflbk Vbulk- Iin-avg 51.2 204.7
Primary Current Control peak primary current known from initial calculations. current sense method allows choosing voltage drop across current sense resistor. Let's value value current sense resistor then evaluated follows:
2.442 0.2047 Ippk
following equation determines peak primary current:
Ippk
voltage drop across sense resistor needs recalculated:
Ippk 0.2047 0.553
Transformer Design Using specified maximum switching frequency nominal output power primary inductance calculated:
bulk- 4.14 Ippk fsw- 0.2047
Using above results value shift resistor
Rshift 0.553 11.06 10-6
highest switching frequency occurs highest input voltage value estimated follows:
-high -low Vbulk- Vbulk-
Time Control value timing capacitor time control calculated minimum bulk capacitor voltage since this condition converter should able deliver specified maximum output power. value timing capacitor then given following equation:
Ippk Vbulk- 4.14 0.2047 55.5 0.12
110.7
EF16 core transformer selected. features cross-section area 20.1 mm2. magnetic allows maximum operating flux density Bmax 0.28 Tesla. number turns primary winding
Ippk 4.14 0.2047 turns 0.28 20.1 10-6
factor transformer's core calculated:
(np)2 4.14 (150)2
Taking into account parasitic internal capacitance connected external timing capacitor should around smaller. value external timing capacitor would appropriate.
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AND8128/D
Start-up Circuit value start-up resistor corresponding start-up time capacitor following:
Rstart-up Vbulk-
Vstart-up CVcc tstart-up
ICC-startMAX
10-9 10-6
5.77
220, R1206 100, R1206 R1206 2.2, R1206 R1206 A9765-A, Coilcraft, 1102 Silver Lake Road CARY 60013 Email: info@coilcraft.com Tel.: 847-639-6400 Fax: 847-639-1469
Feedback Loop output voltage sensed secondary side series connection Zener diode diode inside optocoupler. Resistor reduces maximum current that possibly flow through optocoupler's diode. Resistor introduces bias current Zener diode move operating point toward steeper part characteristic. simple circuit consisting sensing resistor R8//R9, resistor transistor also implements output current limitation. current limitation disabled jumper control signal from secondary side being delivered primary side through optocoupler ISO1. optocoupler injects current from supply capacitor feedback Capacitor bypass capacitor against high frequency noise pick-up. Bill Materials mF/400 mF/400 C0805 C0805 C0805 C0805 nF/Y1 mF/25 mF/25 S250 LL4148 MURA160T3, Semiconductor P6SMB200AT3, Semiconductor MBRS360T3, Semiconductor BZX55C5V6 NCP1215, Semiconductor ISO1 SFH6156 IRFRC20 BC846B 2.7, R0805 R0805 2M7, R1206 220, R0805
Layout NCP1215 designed have power consumption when operating. this reason output currents injected pretty low. Also affected. Therefore proper printed circuit board layout essential reliable operation converter whole operating range. important ensure good grounding technique keep high frequency current loop high voltage areas small possible avoid both magnetic electric field radiations. layout seen Figure
Figure Printed Circuit Board Layout Bottom Side
side assembled with through hole components only. locate those components picture related silkscreen seen Figure
Semiconductor NCP1215 Demo board AC/DC Power Supply +6.8 V/0.8
90-27SVAC
Figure Silkscreen Side
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AND8128/D
bottom side dedicated components. Figure shows their positions. Figure shows same waveforms load condition.
ISO1
Figure Silkscreen Bottom Side
physical dimensions board 52.5*32.5 Practical Results application measured different conditions. following pictures depict typical waveforms several most important points. Figure demonstrates control signals current sense (middle trace) OFF-time timing capacitor's voltage (bottom trace) connected gate driver output depicted trace proper synchronization. picture captured minimum input voltage nominal load.
Figure Voltage Load
Figure demonstrates start-up sequence supply voltage input voltage. trace gate driver voltage. bottom trace supply voltage measured pin.
Figure Supply Voltage Start-Up Figure Voltage Full Load
same situation input voltage depicted Figure
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AND8128/D
SWITCHING FREQUENCY (kHz) OUTPUT POWER
Figure Supply Voltage Start-Up
Figure Switching Frequency Output Power
Since adapter incorporated output current limitation, Figure shows output characteristics.
OUTPUT VOLTAGE OUTPUT CURRENT
dependency switching frequency input voltage estimated when comparing Figure with Figure
SWITCHING FREQUENCY (kHz) OUTPUT POWER
Figure Output Characteristics
switching frequency variation over operating load range essential NCP1215 operation. Figure demonstrates operation variable OFF-time block also frequency compression VDC.
Figure Switching Frequency Output Power
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AND8128/D
most important parameters that characterize power supply power conversion efficiency. Figure shows achieved results line Figure high line.
EFFICIENCY OUTPUT POWER
Last least parameter interested power consumption no-load condition. frequency fold-back achieved values outstanding. line power supply consumed only 20.3 high line increased power loss start-up resistors consumption increased 57.7
Gate-Source Resistor Design Guidelines
Figure Power Conversion Efficiency
some applications, there need wire resistor between MOSFET gate source connections. This preclude eventual MOSFET destruction production stage, converter powered whilst gate left unconnected. However, dealing with extremely startup current implies careful selection gate-source resistance. With NCP1215, gate-source resistor must calculated allow growth capacitor order interfere with power-on sequence. following equation helps deriving Rgate-source, accounting minimum rectified input voltage startup resistor: Vinmin Rgate-source/(Rgate-source Rstartup) take Vinmin VDC, startup resistor then Rgate-source equals minimum normalized value.
EFFICIENCY
OUTPUT POWER
Figure Power Conversion Efficiency
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AND8128/D
Notes
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Semiconductor registered trademarks Semiconductor Components Industries, (SCILLC). SCILLC reserves right make changes without further notice products herein. SCILLC makes warranty, representation guarantee regarding suitability products particular purpose, does SCILLC assume liability arising application product circuit, specifically disclaims liability, including without limitation special, consequential incidental damages. "Typical" parameters which provided SCILLC data sheets and/or specifications vary different applications actual performance vary over time. operating parameters, including "Typicals" must validated each customer application customer's technical experts. SCILLC does convey license under patent rights rights others. SCILLC products designed, intended, authorized components systems intended surgical implant into body, other applications intended support sustain life, other application which failure SCILLC product could create situation where personal injury death occur. Should Buyer purchase SCILLC products such unintended unauthorized application, Buyer shall indemnify hold SCILLC officers, employees, subsidiaries, affiliates, distributors harmless against claims, costs, damages, expenses, reasonable attorney fees arising directly indirectly, claim personal injury death associated with such unintended unauthorized use, even such claim alleges that SCILLC negligent regarding design manufacture part. SCILLC Equal Opportunity/Affirmative Action Employer.
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AND8128/D

INTRODUCTION goal this paper present design example rated AC-DC adapte

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