Figure 1. 20 W Continuous, 43 W Peak Audio Amplifier Power Supply, Designed Around a PKS606P Device.

DI-134

February 2007

Application

Device

Power Output

Input Voltage

Output Voltage

Topology

Audio

PKS606P

20 W, 43 W peak

90-265 VAC

12 V

Flyback

Design Highlights

• Delivers>2Xpeakpowerwithoutoutputdistortion

• Universalinputvoltagerangeoperationallowsasingle

designtobesoldworldwide

• Highefficiency(>79%)acrossentireinputrange

• MeetsEN55022BconductedEMIlimits

• Auto-restartfeatureallowsindefinitelyshortedoutput

• Thermalshutdownprotectssupplyandamplifier

Operation

TheisolatedflybackconvertershowninFigure1wasdesigned

aroundamemberofthePeakSwitchICfamily,thePKS606P

(U1).AdeviceinthePpackage(8-pinDIP)wasselectedto

minimizethecostandsizeoftheheatsinkrequiredforpeak

powerdelivery.

Theinputcircuitryconsistsofafuse(F1)andEMIfilter

components(R6,C9,L8,L4,C12,R9,R8andC13).TheAC

inputisrectified(D1–D4)andfiltered(C2)andconnected

acrosstheprimarysidepowercomponents(T1andU1).

Duringtheflybackportionofeachswitchingcycle,anRCD-

Zenerclampcircuit(L2,D5,R7,C11andVR1)protectsthe

MOSFETintegratedwithinU1.FerritebeadL2,andRC

snubberR7andC11reduceEMIbydampinghigh-frequency

ringing.CapacitorC4decouplestheBYPASS(BP)pinof

U1, which is the IC’s internally regulated supply node.

Anintegrated,high-voltagecurrentsourceprovidesinitial

operatingpowertoU1.AbiaswindingonT1(pins4and

5),D6,C5andR3provideoperatingcurrenttoU1,after

initialstartup.Outputvoltagefeedbackiscoupledacross

thesafetyisolationbarrierbyU2.TransistorQ1,C19,R14

andD9preventthehigh-frequencygainlossthattheU2

phototransistornormallyexperiences,whichpreventsgroups

ofenabledanddisabledswitchingcycles(pulsebunching).

UsingthesignalontheEN/UVpin,thecontrollerwithin

U1regulatestheoutputvoltagebyenablinganddisabling

MOSFETswitchingcycles.

Onthesecondarysideoftheisolationbarrier,D7rectifiesthe

outputofT1andchargesC7andC16.Thesnubbercircuit

(R5andC10)acrossD7attenuatesthehighfrequencyring

thatoccurswhenD7turnsoff.

Outputvoltagefeedbackisderivedfromtwoseparatecircuits.

ThecircuitformedbyVR2,theLEDinU2,C19andR16

providesthehighfrequency(HF)portionofthefeedback

®

D1-D4

1N4005

D7

SB580

VR1

P6KE200A

200 V

VR2

1N5238B

8.7 V

VR3

1N53538

16 V

R6

2.2 M

Ω

1/8 W

R4

1 k

Ω

R10

2 k

Ω

R11

1 k

Ω

R12

8.45 k

Ω

1%

R14

51 k

Ω

R16

1 k

Ω

R13

1 k

Ω

1%

C2

150

µF

400 V

C12

2.2 nF

1 kV

C13

39 pF

1 kV

C4

330 nF

50 V

R15

20

Ω

1/8 W

D9

1N4148

C5

47

35 V

Q1

2N3904

C9

220 nF

275 VAC

C17

150 nF

50 V

C16

220

25 V

C7

220

25 V

C19

470 nF

50 V

U3

TLV431

C18

6.8 nF

50 V

D6

1N4148

12 V, 1.7 A

3.6 A PK

RTN

D5

1N4937

C10

1.2 nF

100 V

C6

2.2 nF

250 VAC

EE25

T1

C11

470 pF

1 kV

R5

10

Ω

1/2 W

R9

3.3

Ω

1/8 W

R1

3.9 M

Ω

1/8 W

R7

300

Ω

1/8 W

R3

4.7 k

Ω

U2B

PC817D

U2A

PC817D

9,10

6,7,8

3

5

4

2

F1

2 A

PI-4580-022307

U1

PKS606P

PeakSwitch

D

S

L

N

EN/UV

BP

L2

3.3

µH

3 A

FB

L4

5 mH

L8

1.8

R8

22

Ω

1/2 W

Design Idea DI-134

PeakSwitch

Audio Amplifier Power Supply