AN376 - STMicroelectronics

APPLICATION NOTE

TEA2260/TEA2261

HIGH PERFORMANCE DRIVER CIRCUITS FOR S.M.P.S

AN376/0694

SUMMARY Page

I INTRODUCTION....................................................... 2

I.1 MASTER SLAVEMODE. ................................................ 2

I.2 BURSTMODE . . . . . . . . . . . . . . . . . ....................................... 2

I.3 OPERATION OF MASTER SLAVEPOWER SUPPLYIN TVAPPLICATION . .. . . . . . 2

I.4 SECONDARY REGULATION............................................. 6

I.5 PRIMARYREGULATION . . . . . . . ......................................... 8

II CIRCUIT DESCRIPTION ................................................ 9

II.1 VOLTAGEREFERENCE AND INTERNAL VCC GENERATION. . . . . . . . . . . . . . . . . . . 10

II.2 OSCILLATOR. . . ...................................................... 10

II.3 ERROR AMPLIFIER. . . . . . . ............................................. 12

II.4 PULSE WIDTH MODULATOR . . . . . . . . . . . . . . . ............................. 12

II.5 SOFT START OPERATION . . . . . ......................................... 13

II.6 BURSTGENERATIONIN STANDBY . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

II.7 ISLOGIC............................................................. 14

II.8 SAFETYFUNCTIONS : DIFFERENCESBETWEEN TEA2260 AND TEA2261. . . . . . . 15

II.8.1 I max. . . . . . . . . . . . . . . . . . . . . . . . . ....................................... 16

II.8.1.1. First thresholdVIM1 . . . . . . . . . ......................................... 17

II.8.1.2. Second thresholdVIM2 for TEA2260 . .................................... 18

II.8.1.3. Second thresholdVIM2 for TEA2261 . .................................... 18

II.8.2 Logical block. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .................... 18

II.8.2.1. Logicalblock for TEA2260 . . . . . . . . . . . . . . . . . . . . . . . . . . ................... 18

II.8.2.2. Logicalblock for TEA2261 . . . . . . . . . . . . . . . . . . . . . . . . . . ................... 19

II.9 OUTPUTSTAGE . . . .. . . . .. . . . . . . . . . . . . . . . . . . . . . .. . . ................... 19

III TV APPLICATION 120W 22O VAC 16KHz SYNCHRONIZED ................... 20

III.1 CHARACTERISTICSOF APPLICATION. . . . . . . ............................. 20

III.2 CALCULATIONOF EXTERNAL COMPONENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

III.2.1 Transformer calculation. . . . . . . . . . . ....................................... 21

III.2.1.1 Transformerspecification . . . . . . . ....................................... 22

III.2.2 Switching transistorand its base drive . . . . . . . . . ............................. 22

III.2.2.1 Currentlimit calculation. . . ............................................. 22

III.2.2.2 Snubbernetwork. . . . . . . . ............................................. 23

III.2.2.3 Base drive. . . . . . . . . . . . . . . . . . . ....................................... 24

III.2.3 Oscillator frequency . .. . . . . ............................................. 25

III.2.4 Regulationloop. ....................................................... 25

III.2.5 Overloadcapacitor . . . . . . . . . . . . ......................................... 26

III.2.6 Soft startcapacitor . . . . . ................................................ 26

III.2.7 Feedback voltagetransformer . . . . . ....................................... 26

III.2.8 Start up resistor. .. . . . . . . . . . . . . . . ....................................... 27

III.2.9 High voltagefiltering capacitor . . . . . . . . . . . . . . . ............................. 28

III.3 ELECTRICAL DIAGRAM . . . . . . . . . . . . . . . . . . . . . . .. . . . . . ................... 29

1/33

SUMMARY (continued) Page

IV TV APPLICATION 140W 220 VAC 32kHz SYNCHRONIZED .................... 32

IV.1 APPLICATIONCHARACTERISTICS . . . . . . . . . . . . . .......................... 32

IV.2 TRANSFORMER CHARACTERISTICS . .................................... 32

IV.3 ELECTRICAL DIAGRAM . . . . . . . . . . . . . . . . . . . . . . .. . . . . . ................... 33

V TV APPLICATION 110W 220 VAC 40kHz REGULATED BY OPTOCOUPLER...... 34

V.1 FREQUENCY SOFT START . . . . ......................................... 34

V.2 APPLICATIONCHARACTERISTICS . . . . . . . . . . . . . .......................... 34

V.3 TRANSFORMER SPECIFICATION . . . . . . . . . . . ............................. 34

V.4 ELECTRICAL DIAGRAM . . . . . . . . . . . . . . . . . . . . . . .. . . . . . ................... 35

I - INTRODUCTION

The TEA2260/61 is an integrated circuit able to

drive a bipolar transistor directly with an output

base current up to 1.2A.

So the TEA2260/61 covers a wide range of appli-

cation from 80Wto more than 200Wwith all safety

requirements respected.

The high performancesof theregulation loop pro-

vide a very low output power due to an automatic

burst mode.

The TEA2260/61 can be used in a MASTER

SLAVE STRUCTURE, in a PRIMARY REGULA-

TION or a SECONDARYREGULATION.

The TEA2260/61isveryflexibleand high perform-

ance device with a very large applications field.

The only difference between TEA2260 and

TEA2261 concerns security functions (see para-

graph II.8)

I.1 - MasterSlave Mode (Figure 1)

In this configuration the master circuit located on

the secondaryside, generates PWM pulses used

for outputvoltageregulation.Thesepulsesaresent

via a feedback transformer to the slave circuit

(Figure 1).

In this mode of operation, the falling edge of the

PWMSignal may besynchronized with anexternal

signal. By this way the switching off time of the

power transistor,which generateslot of parasites,

can be synchronized on the line flyback signal in

TV applications.

An other advantage of the MASTER SLAVE

STRUCTURE isto havea very goodregulationnot

depending of the coupling between transformer

primary and secondarywindings, which allows the

use of lowcost switchmode transformers.

I.2 - Burst Mode (Figure 2)

Duringstart-upandstand-byphases,noregulation

pulses are provided by the master circuit to the

slavecircuit.

The slave circuit operates in primary regulation

mode. When the outputpower is very lowthe burst

mode is automaticallyused.

This operating mode of the SMPS effectivelypro-

videsa verylowoutputpowerwithahighefficiency.

The TEA2260/61 generates bursts with a period

varying as a functionof the output power.

Thus the output power in burst mode can varied in

a wide range from 1W to more than 30W.

I.3 - Operation of Master Slave Power Supply

in TVApplication

The systemarchitecture generallyemployed isde-

picted in Figure 3. On the secondary side a micro

controller is connected to the remote control re-

ceiverwhich generatescontrolsignalforthestand-

by and normal modes of operation (Figure 4).

- Instand-bymode,the devicepowerconsumption

is very low (few watts). The master circuit does

not sendpulsesandhencetheslavecircuitworks

in primaryregulationand burst mode.

- In the normal mode, the master circuit provides

the PWMsignalrequiredforregulationpurposes.

This iscalled MASTERSLAVE MODE. The mas-

ter circuit can be simultaneously synchronized

with the line flybacksignal.

- Power supplystart-up. As soon as the VCC(start)

threshold is reached, the slave circuit starts in

continuous mode and primary regulationas long

as the nominaloutput voltages are not reached.

After thisstart-upphasethe microcontrollerholds

the TV Set in stand-bymode or either in normal

mode.

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SLAVE

CIRCUIT MASTER

CIRCUIT

Sync.

Pulses

Pulse

Input

Base

Current

PWM

Signal

376-01.EPS

Figure1

BurstPeriod

typ 30ms

COLLECTORCURRENT ENVELOP DETAILOF ONE BURST

Switching

Period

376-02.EPS

Figure 2 : Burst ModeOperation

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AUDIO

OUTPUT

STAGE

SCANNING

DEVICE

TEA5170

MAINS

INPUT

TEA2260/61

VOLTAGE

REGULATOR

µP

INFRA-RED

RECEIVER

Muting

Control

Remote

Stand-by

Remote

Stand-by

Synchronization

VCC

P : Output voltage adjustementin normal mode

P : Output voltage adjustementin stand-by

Small signalprimary ground

Power primary ground

Secondary ground(isolated from mains)

PWM

376-03.EPS

Figure 3 : TV ApplicationSystem Diagram

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Start-up Stand-by Normaloperation Stand-by

Stand-by

control

voltage

µP supply

voltage

TEA5170

Output voltage

envelop

Output

voltage

Collector

current

envelop

CC(START)

CC(STOP)

TEA2260/61

V voltage

* t and t : commands issued by µP

376-04.EPS

Figure 4 : SystemDescription (waveforms)

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I.4 - SecondaryRegulation (Figures5 and6)

In this configurationthe TEA2260/61 provides the

regulationthrough an optocouplerto ensure good

accuracy.

The advantageof this configurationis the avaibility

of a large range of output power variation (e.g 1W

to 110W).

This feature is due to the automatic burst mode

(see paragraphII.6).

The structure in a TV Set is simpler than the

MASTER SLAVE STRUCTURE because the

power supply switches from normalmode to burst

mode automatically as a function of the output

power.

AUDIO

OUTPUT

STAGE

SCANNING

DEVICE

MAINS

INPUT

TEA2260/61

VOLTAGE

REGULATOR

µP

INFRA-RED

RECEIVER

Muting

Control

Remote

Stand-by

VCC

P : Outputvoltageadjustement

Smallsignal primaryground

Powerprimaryground

Secondaryground(isolated from mains)

376-05.EPS

Figure 5 : TV ApplicationSystem Diagram

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Start-up Stand-by Normaloperation Stand-by

1µP supply

voltage

Output

voltage

Collector

current

envelop

CC(START)

CC(STOP)

TEA2260/61

V voltage

* t and t : commands issued by µP

Stand-by

voltage

envelop

376-06.EPS

Figure 6 : SystemDescription (waveforms)

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I.5 - PrimaryRegulation (Figure 7)

In this configurationthe TEA2260/61 provides the

regulationthrough anauxilliary winding.

This structure is very simple but the accuracyde-

pends on the coupling between the transformer

primaryand secondarywinding.

Due to the automaticburst mode the outputpower

can varyin a large range.

AUDIO

OUTPUT

STAGE

SCANNING

DEVICE

MAINS

INPUT

TEA2260/61

VOLTAGE

REGULATOR

µP

INFRA-RED

RECEIVER

Muting

Control

Remote

Stand-by

VCC

P : Output voltage adjustement

Small signalprimaryground

Power primary ground

Secondary ground (isolated from mains)

376-07.EPS

Figure 7 : TV ApplicationSystem Diagram

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II - CIRCUITDESCRIPTION

Figure 8 showsthe integratedfunctions.

16 15

3821

1011

94512 13

ERROR AMPLIFLIER

INTERNAL

BIAS

MODULATOR

LOGIC

AUTOMATIC

BURST

GENERATION

LOGIC LOGIC

PROCESSOR

V MONITORING

REF

V (2.49V)

POSITIVE

OUTPUT

STAGE

NEGATIVE

OUTPUT

STAGE

REPETITIVE

OVERLOAD

PROTECTION CURRENT

LIMITATION

SECONDARY

PULSE

0.15V 0.6V2.55V 0.9V

10µA

45µA

PRIMARY

PULSES REGULATION

PULSES

OVERVOLTAGE

PROTECTION

15.7V

DEMAGNETIZATION

SENSING

MODULATORS

2.49V

REF 7.4V 10.3V

OSCILLATOR

ON(Max.)

+ 1.2A

(Max.)

SV V+

OUT

GNDIMAX

INISCC

100

T (60%)

SOFT-START

-1

-2A

(Max.)

376-08.EPS

Figure8

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The circuitcontains 8 blocks :

- Voltagereferenceand internalVCC generation.

- RC oscillator

- Error amplifier

- Pulse widthmodulator(PWM)

- ”Is logic”for transformerdemagnetization check-

ing.

- Currentlimitation sub-unit(IMAX)

- Logicalblock.

- Outputstage.

II.1 - VoltageReference and Internal VCC Gen-

eration (Figure 9)

This block generatesa 2.5V typ. voltagereference

valid as soon as VCC exceeds4V. It is not directly

accessible externally but is transmitted to other

blocks of the circuit.

This block also generates an internal regulated

VCC,V

CC(int), the nominal value of which is 5V.

VCC(int) suppliesthe circuit when Vcc is higher than

VCC(start) (10.3V typ.).

This allows the circuit to achieve a good external

VCC rejection, and to provide high performance

even with large VCC supplyvoltage variations.

This block alsogenerates initialization and control

signals for the logical block. It also contains the

VCC(Max.) comparator(typ threshold 15.7V).

II.2 - Oscillator(Figures 10 and 11)

The oscillator determines the switching frequency

in primary regulation mode. Two external compo-

nents are required : a resistorROand a capacitor

CO. The oscillator generates a sawtooth signal,

which is availableon Pin 10.

376-09.EPS

Figure 9 : VoltageReference Block Principle

376-10.EPS

Figure 10 : OperatingPrinciple

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COcapacitor is charged with a constant current.

The current is fixed by ROwhich is supplied by

voltage VREF.

Ich =2.5

When the voltage across COreaches

3xV

CCint (typ3.33V), Q Transistor conducts and

COisquickly dischargedinto an 2kΩ(typ) internal

resistor. When the voltage reaches

1/3 x VCCint (typ 1.66V), the discharge is stopped,

and the linearcharge startsagain.

Theoreticalvalues ofT,T1and T2as function of RO

and CO:

T=C

O(0.69 x RO+1380)

T1=ROxCOx 0.69

T2=COx 2000 x 0.69 = COx 1380

Due to the time response of comparators and

normal spread on thresholds values, the real val-

uesofT1andT2maybeslightlydifferent,compared

with these theoreticalvalues (see Figure 12).

376-11.EPS

Figure11 : Sawtoothavailable accross CO

376-12.EPS

Figure 12 : Frequency asa Functionof ROand CO

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376-14A.EPS / 376-14B.EPS

Figure14

II.3 - Error Amplifier (Figure13)

Itismadeofanoperationalamplifier.Theopenloop

gain is typically 75dB. The unitygain frequencyis

550kHz (typ). An internalprotection limits the out-

put current (Pin 7) at 2mA in case of shorted to

ground.

376-13.EPS

Figure13

Output and inverting input are accessible thus

giving highflexibility in use.Thenon-invertinginput

is not accessible and is internally connected to

VREF (or0.9VREF inburstmode-seeparagraphII.6)

Before driving the pulse width modulator (PWM)

and in order to get the appropriatephase, the error

amplifier is followed by an inverter.

II.4 - Pulse Width Modulator (PWM) (Figure14)

The pulse width modulator consists of a compara-

torfedbytheoutputsignaloftheerroramplifierand

the oscillator output. Its outputis used to generate

conductionsignal.

The TEA2260/61actually integrates two PWM :

- AmainPWM generatesaregulationsignal(∝)by

comparing the error signal (inverted) and the

sawtooth.

- An auxiliary PWM generates a maximum duty

cycle conduction signal (β), by comparing the

sawtooth with an internal fixed voltage. Further-

more, during the starting phase of the SMPS, in

association with an externalcapacitor, this PWM

generatesincreasingduty cycle, thus allowing a

”soft” start-up.

- A logic ”AND” between signals (∝) and (β) pro-

videsthe primaryregulator output signal TA.

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376-16.EPS

Figure 16 : C1 Voltage(Pin 9)

376-15.EPS

Figure15

II.5 - Soft Start Operation (Figure16)

From t1to t2, there is no output pulse (pin 14) and

C1is chargedby a180µAcurrent (typically). When

C1voltagereaches 1.5V (typically), output pulses

appear and the chargecurrent of C1is divided by

20 (9µA typically), then the duty cycle increases

progressively.WhenC1voltagereaches2.7V(typi-

cally), the soft-starting device ceases to limit the

duty cycle, whichmay reach 60%.

UnderestablishedconditionsC1voltageischarged

to 3.1V(typically)

II.6 - Burst Generationin Stand By (primary

regulationmode)

When the SMPSoutput powerbecomes very low,

the dutycycleoftheswitchingtransistorconduction

becomes also very low. In order to transmita low

average power, while ensuring correct switching

conditionsto thepower transistor,a ”burst” system

is usedfor energytransmission in standby mode.

Principle

For a medium outputpower (e.g. morethan 10W),

the voltage reference is applied to the non- invert-

ing input of the error amplifier. When output power

decreasesas the minimum conductingtime of the

power transistor is reached, the output voltage

tends to increase. Consequently the error signal

appliedto the PWM becomes higherthan the saw-

tooth. This is detected by a special logic and the

voltageapplied tothe noninverting input becomes

VREF = 0.9 x 2.5 = 2.25V typically.

Consequentlythe regulation loop is in an overvol-

tageequivalentstate and the outputpulses disap-

pear. The output voltage decreases and when it

reaches a value near 0.9 timesthe normalregula-

tion value , thevoltage appliedtothe non inverting

input is switched again to the normal value

VREF = 2.5V.Pulses applied to the powertransistor

reappear,the output voltageincreases again, and

so on... A relaxation operation is obtained, gener-

atingthe burst.

Futhermore,to avoid a current peak at the begin-

ning of each burst, the soft-start is used at this

instant.

Advantages of this method

- improved powersupply efficiencycompared with

traditionalsystems, for low power transmission.

- automatic burst-mode continuousmode transi-

tion, as a functionof the output power.

- high stand-bypower range.

- burst frequency and duty cycle adjustable with

externalcomponents to the circuit.

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376-17.EPS

Figure 17 : IS LogicPrinciple Schematic

376-18.EPS

Figure18

II.7 - IS Logic (Figure17)

During the transition from the ”stand-by” mode to

the ”normal operating” mode, conduction pulses

generated by the secondary regulator occur con-

currently with those from the primary regulator.

These pulses are non-synchronous and this may

be dangerousfor the switching transistor. For ex-

ample if the transistoris switched-onagain during

the overvoltage phase,just afterswitching-off, the

FBSOA may not be respected and the transistor

damaged.

Tosolvethisproblemaspecialarrangementcheck-

ing the magnetization state of the power trans-

former isused.

The aim of the IS Logicis thereforeto monitorthe

primary regulationpulses (TA) and the secondary

regulationpulses (Pin 2),andtodeliver asignalTB

compatiblewiththe powertransistor safetyrequire-

ments.

The IS Logic block comprises mainly two D flip-

flops.

When a conductionsignal arrives, the correspond-

ing flip-flop is set in order to inhibit a conduction

signalcoming from the other regulationloop. Both

flip-flops are reset by the negative edge of the

signalappliedtothedemagnetizationsensinginput

(Is Pin1).

Note :The demagnetization checking device just

described is only active when there are concur-

rentlyprimaryandsecondarypulses,whichinprac-

tice only occurs during the transient phase from

Stand-bymode to normalmode.

When the power supply is in primary regulation

modeorinsecondaryregulationmode,thedemag-

netization checkingfunction is not activated.

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II.8 - Safety Functions :

Differencesbetween TEA2260and TEA2261

TEA2260

Concerning the safety functions,VCC(max) (over-

voltage detection)VIM1,VIM2 (overcurrentdetec-

tion) the TEA2260uses an internal counter which

is incrementedeachtimeVCCstop isreached (after

fault detection) and try to restart. After 3 restarts

with fault detectionthe power supply stops. But in

certain cases where the TV set is supplied for a

long time,withoutswich off,thepower supplycould

stop (cases of tube flashes). In this case it is

necessary to switch off the TV set and swich on

again to reset the internalcounter.

TEA2261

The safety detections are similar to TEA2260 for

VCC(max) (overvoltage detection) VIM1, VIM2

(overcurrentdetection),but eachtimeafault detec-

tion is operatingthe C2capacitoris loaded step by

step up to 2.6V,(case of long durationfault detec-

tion)and the power supply stpos. To discharge C2

capacitoritisnecessarytoswitchofftheTVsetand

to switch on again and the power supplystarts up.

S.M.P.S.

starting

First

threshold reached

VIM1

Pulseby pulse current

limitingC charged

V < 2.6V

V max

reached

S.M.P.S. stopping

V stop reached

N=N+1

Normaloperating

C discharged

Restart

number= 3

Definitive

stopping

Reset C

discharged

Second

threshold reached

VIM2

376-19.EPS

Figure 19 : TEA2260Safety Functions Flowchart

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S.M.P.S.

starting

First

thresholdreached

VIM1

V < 2.6V

V max

reached

Normaloperating

C discharged

Definitive

stopping

Pulse by pulsecurrent

limitingC charged

C charged

S.M.P.S. stopped

V < 2.6V

C2 Y

Reset C

discharged

Second

thresholdreached

VIM2

376-20.EPS

Figure 20 : TEA2261Safety Functions Flowchart

II.8.1. I Max (power transistorcurrent limitation)

The current is measured by means of a resistor

inserted in the emitter of the powertransistor. The

voltage obtained is applied on Pin 3 of the

TEA2260/61.

The currentlimitation device of the TEA2260/61 is

a double threshold device. For the first threshold,

there isnodifferencebetweenthetwodevices,only

for the secondthreshold.

376-21.EPS

Figure 21

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II.8.1.1- Firstthreshold : VIM1 (typicalvalue)

376-22.EPS

Figure 22 : Current Limitation SchematicPrinciple. First ThresholdPart.

Two actionsare carriedout when thefirst threshold

is reached

- The power transistor is switched-off (pulse by

pulse limitation). A new conductionpulse is nec-

essaryto switch-on again.

-TheC

2capacitor, which is continuously dis-

charged by Idisch current (10µA typically), is

chargedby the current

Ich - I disch (45µA-10µA=35µA typically), until

the nextconduction pulse.

The capacitor C2is chargedas long as an output

overload is triggering the first current limitation

threshold.When thevoltageacrossC2reachesthe

threshold VC2 (typically 2.55V), output pulses

(pin 14) are inhibitedand the SMPSis stopped.

Arestartmay beobtainedbydecreasingVcc under

the VCC(stop) thresholdto resetthe IC.

If the output overload disappears before the volt-

age across C2reaches VC2, the capacitor is dis-

charged and thepower supplyis not turned off.

Due to this feature, a transient output overload is

tolerated, depending on the value of C2(see

III.2.5).

376-23.EPS

Figure 23 : Exampleof First Current LimitationThreshold Triggering

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376-24.EPS

Figure 24 : TEA2260Simplified Logical Block Diagram

II.8.1.2- Secondcurrent limitation threshold

(VIM2) for TEA2260

In caseof hardoverload orshortcircuit, despitethe

pulse by pulse current limitation operation, the

current in the power transistor continues to in-

crease. If the second threshold VIM2 is reached,

the powersupply isimmediately turnedoff andthe

internalcounterisincremented.After3restarts,the

power supply is definitively stopped.Restartis ob-

tained bydecreasingVCC belowVCC(stop), asin the

case of stopping due to the repetitive overload

protectiontriggering.

II.8.1.3- Secondcurrent limitation threshold

(VIM2) for TEA2261

For this device, if the second thresholdis reached,

the powersupplyis turnedoff, C2ischarged and a

new start-upis authorizedonlyif VC2 < 2.6V.

II.8.2 - LogicalBlock

This block receives the safety signalscoming from

different blocks and inhibits the conductionsignals

when necessary.

II.8.2.1- Logical block for TEA2260

TB is the conduction signal (primary or

secondary)coming from the Is

logical block.

TC is the conductionsignal transmitted

to the output stage.

I1is theoutputsignalof the firstcurrent

limitation threshold comparator. It is

memorized by the flip-flop B1.

I2is the output signal of the second

current limitation threshold

comparator

VC2 istheoutputsignalofthecomparator

checking the voltage acrossC2.

VCC (Max.) is the signal coming from VCC

checking comparator.

These three signals VC2,I

, Vcc(max) are memo-

rized by B2.

In case of B2flip-flop setting (I2or VC2 or Vcc(max)

defect)the current consumptionon VCC increases.

This function allows to decrease the Vcc voltage

untilVCC(stop). Afterthisthe currentconsumptionon

Vcc decreases to ICC(start) and a new start up is

enabled.

The VCC(Off) signal comes from the comparator

checking VCC. A counter counts the number of

VCC(off) establishment. After four attempted starts

of the power supply the output of the circuit is

inhibited. To reset the circuit it is necessary to

decreaseVCC below5.5V typically. In practice this

means that the power supply has to be discon-

nectedfrom the mains.

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II.8.2.2- Logical block for TEA2261

AND TC

2.6V

8RESET

VCC (Max.)

VCC (off)

376-25.EPS

Figure25

VCC(off) is a signal coming from a comparator

checking VCC. When VCC >V

CC(stop),VCE(off) is

high.

VCC(max) is a signal coming from a comparator

checking VCC. When VCC >V

CC(max),VCC(max) is

high.

I1is a signal coming from thefirst current limitation

thresholdcomparator.

When Imax xR

SHUNT >VIM1, I1is high.

I2is a signal coming from the second current limi-

tationthresholdcomparator.

When Imax xR

SHUNT >VIM2,I2is high.

TB is the conduction signal coming from the error

ampliflier system.

TC is the output signal transmitted to the output

stage.

II.9 - Output Stage

The output stage is made of a push-pull configura-

tion : the uppertransistoris usedfor power transis-

tor conduction and the lower transistor for power

transistor switch-off.

A capacitive coupling is recommanded in orderto

provide a sufficientnegative base currentthrough

the powertransistor .

376-26.EPS

Figure26

HIGH PERFORMANCE DRIVER CIRCUITS FOR S.M.P.S

19/33

376-27.EPS

Figure 27 : Typical Voltage Drops of Output Transistor versus Current

Important remark : Due to the internal output

stage structure, the output voltage (Pin 14) must

never exceed5V. This conditionis respectedwhen

a bipolartransistor is driven.

Note that Power-MOS transistor drive is not possi-

ble with the TEA2260/61.

III - TV APPLICATION 120W - 220 VAC - 16kHZ

SYNCHRONIZED ON HORIZONTAL DEFLEC-

TION FREQUENCY

General structure and operational features of this

power supply were outlinedin sectionI.

The detailscoveredbelow applyto apower supply

application using the master circuit TEA5170.

(refer to TEA5170data sheetand TEA5170 appli-

cation note ”AN088” for furtherdetails).

III.1 - Characteristicsof Application

- Discontinuousmode Flyback SMPS

- Standby function using the burst mode of

TEA2260/61

- SwitchingFrequency

- Normal mode : 15.625 kHz (synchronized on

horizontal deflectionfrequency)

- Standbymode : about16kHz

- Nominal mains voltage : 220VAC

Mains voltage range : 170 VAC to 270 VAC

- Nominal output power : 120W

- Output power range in normal mode

14W < PO< 120W

- Output power range in standby mode

1W < PO< 25W

- Efficiency

- Normal mode : 85% (under nominal conditions)

- Stand by mode : 45%

- Regulationperformance on high voltage output :

140 VDC

-±0.3% versus mains variations of 170 VAC to

270 VAC (POUT : 120W)

-±0.5% versusload variations of 14W to 120W

(Vin =220 VAC)

- Overloadprotection and complete shut down af-

ter a predeterminedtime interval.

- Shortcircuitprotection.

- Open load protection by output overvoltage de-

tection

- Complete power supply shut-down after 3 re-

startsresultinginthedetectionofafaultcondition.

- Complete power supply shut-down when VC2

reaches2.6V for TEA2261.

III.2 - Calculation of External Components

Also refer to TEA5170 application note ”AN-088”

for calculation methods applicable to other power

supplycomponents.

The external components to TEA2260/61 deter-

mine the following parameters :

- OperatingFrequency in primaryregulation

- Minimumconductiontime in primaryregulation

- Soft start duration

- overloadduration

- Error amplifier gain and stand-byoutput voltage

- Basedrive of the switching transistor

- Primary current limitation

Ideal values

- Freerunning Frequency in stand-by mode :

16kHz

-Ton

(min) duration: 1µs

- Soft start duration: 30ms

- Maximum overloadduration: 40ms

- Error amplifier Gain : 15

- Maximum primary current depends on the trans-

former specifications

HIGH PERFORMANCE DRIVER CIRCUITSFOR S.M.P.S

20/33

III.2.1 - Transformer calculation

The following important features must be consid-

ered to calculate the specifications of the trans-

former :

- Maximumoutput power : 120W

- Minimuminput voltage:

- 220 VAC- 20%→Vin(min) = 210 VDCwith 40V

ripple on the high voltage filtering capacitor

- SwitchingFrequency : 15.625kHz

- Maximumduty cycle : 0.45

- Outputvoltages :

+ 140V - 0.6A

+ 14V - 0.5A

+ 25V - 1A

+ 7.5V - 0.6A

+ 13V - 0.3A

Maximum primary current

IP(max)=2x P

OUT

ηxVIN(min)xTON(max)

η: efficiency of the power supply 0.80 < η < 0.85

Primary inductance of the transformer

LP=VIN(min)

IP(max)xTON(max)

Transformer ratio

np =(VOUT +VD)xT

VIN(min)xT

ON(max)

Reflectedvoltage

VR=1

TON(max)−1xVIN(min)

Overvoltagedue tothe leakageinductance

VPEAK =IP(max)

2x√Lf

with : Lf = leakage inductanceof the transformer

0.04 x Lp < Lf < 0.10x Lp

C =capacitorof the snubbernetwork(see III.2.2.2)

376-28A.EPS/ 376-28B.EPS

Figure28

HIGH PERFORMANCE DRIVER CIRCUITS FOR S.M.P.S

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Numericalapplication

To determinate the specifications of the trans-

former, it is necessary to make a compromise

between a maximum primary current and a maxi-

mum voltage on the transistor:

- Tominimize the maximum primary current

with 0.4 < TON(max)

T<0.5

- Tominimize the maximum voltage on the transis-

tor during the demagnetizationphase.

0.3 < TON(max)

T<0.4

When the output power of the power supply is

greater than 100W it is better to minimize the

maximumprimary currentbecausethecurrentgain

Bf=I

C/I

Bof bipolartransistor is 1.5 < Bf<6

Choice : TON(max)

T<0.45

IP(MAX)=2xP

OUT

ηxVIN(MIN)xTON(MAX)

=2x120

0.85 x 210 x 0.45 =3A

LP=VIN(MIN)

IP(MAX)xT

ON(MAX)=210

3x0.45 x 64 10−6=1.95mH

VR=1

TON(MAX)−1xV

IN(MIN)=1

0.45 −1x210=172V

VPEAK will be calculated with the snubber network

determination(see II.2.2.2.1)

III.2.1.1 - Transformer specification

- Reference: OREGA- SMT5 - G4467-03

- MechanicalData :

- Ferrite : B50

- 2 cores: 53 x 18 x 18 (mm) THOMSON-LCC

- Airgap : 1.7 mm

- ElectricalData :

Winding Pin Inductance

nP3-6 1.95µH

nAUX 7-9 8.1µH

n2 19-13 770µH

n3 19-20 8.2µH

n4 14-17 4.2µH

n5 22-21 31.7µH

376-29.EPS

Figure 29

III.2.2 - Switching transistorand its base drive

III.2.2.1- First current limitation

376-30A.EPS / 376-30B.EPS / 376-30C.EPS

Figure 30 : CurrentLimitation

Note : in currentlimitation TIBon < TON

HIGH PERFORMANCE DRIVER CIRCUITSFOR S.M.P.S

22/33

The currentmeasurementis IE=I

B+IC

The maximumcollector current calculated in III.2.1

is IC(Max.) = 3A (a switching transistor SGSF344

may be chosen)

The current gain is: Bf=IC

IB+=3.5

The currentlimitation is :

IE(max)=IP(max)−(TSxVIN(min)

LP)+IB+

with : TS= storage time of theswitching transistor

(typ 3µs) and VIM1 = first threshold of current

measurement(typ 0.6 v)

RSHUNT =VIM1

IE(max)

Numericalapplication

IE(max)=IP(max)−(TSxVIN(min)

LP)+IB+

IE(max)=3−(310

−6x210

1.95 10−3)+0.85 =3.55A

RSHUNT =VIM1

IE(max)=0.6

3.255 =0.169Ω

III.2.2.2- Snubber network

AR.D.C network isused to limit the overvoltageon

the transistorduringthe switching off time.

When the transistoris switched off, the capacitoris

charged directly through the diode.

When the transistoris switched on,thecapacitoris

dischargedthrougha resistor.

-C=I

P(max)xtf

2xVCEO

-3xRxC=T

on(min)

(to discharge the capacitor C by the correct

amount)

- Maximumpower dissipated in R :

P=1

2xCx(V

IN(max)+VR)2xF

376-31A.EPS/ 376-31B.EPS

Figure 31

Numerical application(with SGSF344 transis-

tor) with:

IP(Max.) =3A-V

IN(Max.) = 370 VDC

tf= 0.3µs-V

R= 172V

VCEO = 600V - F = 16kHz

TON(Min.) =4µs

C=I

P(max)xtf

2xVCEO

=3x0.3 10−6

2x600

=2.25nF

R=TON(min)

3xC =410−6

3 x 2.25 10−9=560Ω

P=1

2xCxV

IN(max)+VR)2xF

P=1

2x 2.25⋅109x(370 +172)2x16⋅103=5.29W

In the final applicationa value of 2.7nF is chosen

to decrease the overvoltage on the transistor in

shortcircuit condition.

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III.2.2.2.1- Overvoltage due to the leakagein-

ductance (See. III.2.1)

The capacitorC ofthe snubbernetworkinfluences

the overvoltagedue to the leakageinductance.

Vpeak =IC(max)

2√Lf

Numericalapplication

with : Lf= 0.08 x Lp= 0.08 x 1.9 10 -3 = 152µH

Vpeak 3

2x√152 106

2.25 109=390V

so VCE(Max.) =V

IN(Max.) +V

R+V

peak =V

CE(Max.) =

370 + 172 + 390 ≅930V

III.2.2.3- Basedrive

The output stage of the TEA2260/61 works in

saturation mode and hence the internal power

dissipation is very low.

R1 =VCC+−V

P−V

Z−V

IB+

376-32A.EPS / 376-32B.EPS

Figure 32

Numericalapplication

R1 =13 −0.9 −3−0.6

0.85 ≅10Ωin this case the current gain, BF =IC

IB=3

0.85 =3.5 but it is recom-

manded to verify the VCE sat dynamicbehaviouron the transistoras follows: see Figure 33

376-33A.EPS/ 376-33B.EPS

Figure33

Ideal value : 1V ≤VCEsat +V

D≤2V

Remark : The mains of the TEA2260/61 must be provided

through an isolation transformer for this measurement

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III.2.3 - Oscillatorfrequency

The free runningfrequencyis given on II.2.

The typical value of minimum conduction time Ton(min) on the output of the TEA2260/61 is given by:

Ton(min) =1040 x CO

Note : the minimum conduction time TON(min) on the transistor is longerdue to the storagetime.

376-34.EPS

Figure34

Numericalapplication

FO=16kHz

COischosen at 1nF

so TON min on the TEA2260/61= 1µs

RO=1

FOxC

Ox 0.66 −1.57 103

RO=1

16 103x1 10

−9x 0.66 −1.57 103

RO=93KΩ

O= 100kΩis chosen.

Note :Fo ischosenrelativelylowto avoidmagneti-

zationof the transformerduring thestart-upphase.

III.2.4 - Regulation loop

In stand by mode the error amplifier of the

TEA2260/61carries out the regulation.

- The R.C. filter is necessary to avoid the peak

voltage due to the leakage inductance.The time

constant τ=RC is about30µs < R.C. < 150µsas

a function of the transformer technology.

- To achieve a stable behaviour of the regulation

loop and to decrease the ripple on the output

voltage in stand by mode the time constant

shouldbe approximately:

(R1+R2 +R3)xC≅R

OUT xCOUT

376-35.EPS

Figure 35

with : COUT (filtering output capacitor) and ROUT

(load resistoron theoutput instand by mode)

- To ensure a stable behaviour in stand-by mode

the amplifiergain is choosento :

G=R4

R2 +R3 ≅15

Calculation of R, R1, R2, R3, R4

a) The resistor R is givenby

R=τ

C choosen between 1µF<C<10µF

τ=80µs is chosen

C =2.2µF is chosen

HIGH PERFORMANCE DRIVER CIRCUITS FOR S.M.P.S

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Numericalapplication

SOR=τ

C=80 10−6

2.2 10−6=36Ω

b) The resistors R1, R2, R3 are given by

R1 +R2 +R3 ≅COUT xR

OUT

15 x C

with :

Vref : reference voltage of the error amplifier

Vref = 2.5V

Vcc(standby) : Vcc voltagein standby mode.

Vcc(stand by) = 0.9 x Vcc (in normal mode)

Numericalapplication

with :

Vcc =13V

Vref = 2.5V

Rout =2kΩ on output 135 V

Cout = 100µF on output135 V

C = 2.2µF

R1+R2 +R3 ≅COUT xR

OUT

15xC =100 10−6x2103

15 x 2.2 10−6=6kΩ

R2 +R3 =(R1+R2 +R3)xVREF

VCC(stand by)

R2 +R3 =610

3x2.5

0.9 x 13 =1.28kΩ

values choosen :

R2 potentiometerresistor of 1kΩ

R3 fixedresistor 1kΩ

R1 = (R1+ R2 + R3) - (R2+ R3)

R1 = 6k - 1.28k = 4.7kΩ

c) The resistor R4 isgiven byR4≅15x (R2+ R3)

Numericalapplication

R4 ≅15 x (R2+ R3) ≅15 x (1.28 103)≅18kΩ

III.2.5 - Overloadcapacitor

When an overload is detectedwith the first thresh-

old VIM1 the capacitor C2 (pin 8) is charged until

the endof the periodas shown in figure 33.

So the average load current is given by :

IC2 =T−TON

TxI

CH −IDISH

the threshold to cut off the TEA2260/61 power

supply is 2.5V typically and hence the delay time

before overload detection is given by :

Toverload =2.5 x C2

(T−TON

TxI

CH)− I

DISCH

376-36.EPS

Figure 36 : Load of OverloadCapacitor

Numericalapplication

with : maximum overload time = 40 ms

the longer delay time is obtainedwhen

Ton = Ton(max)

C2 =((T−Ton(max)

TxICH)−I

DISCH)xToverload

2.5

C2 =(0.55 x 45 10-6 -10 10

-6 40 10−3

2.5 ≅220nF

Note : in practice, the overload capacitor value

mustbe greater than the soft start capacitor (C2 ≥

C1) to ensure acorrect startup phase ofthe power

supply.

III.2.6 - Soft startcapacitor

Refer to paragraph II.5 for the soft start function

explanation.

Thesoft startduration is given by :

TSOFTSTART =(2.7−1.5)xC1

910

−6

C1=7.5 10−6xTSOFTSTART

Numericalapplication

with : Tsoft start = 30 ms

C1 =7.5 10-6 x3010

-3 = 220 nF

III.2.7 - Feed back voltage transformer

A feedback voltage transformer is used to send

informationfrom the secondarycircuit (master cir-

cuit) to the primary circuit (slave circuit).

This transformer is needed to provide an electric

insulation betweenprimary and secondaryside.

Thefeedbackinput ofTEA2260/61is fedwith logic

level (threshold0.9V)

It is necessaryto havethe same waveform on the

primary side as on the secondaryside.

HIGH PERFORMANCE DRIVER CIRCUITSFOR S.M.P.S

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376-37.EPS

Figure37

For this reason the time constant must be higher

than the maximum conduction time in normal

mode.

Hence the primary inductance Lp must be calcu-

lated as follows: Lp > 3.R.Ton(max)

Numericalapplication

with :

TON(max) =28µs

R=270Ω

p> 3 x 270 x 28 10-6 =22mH

a) When the TEA5170is usedVIN =7V

np =VS(min)

VIN x(1−TON(max)

np =1.5

7x(

1−0.45)=0.389

b) When the TEA2028 is usedVIN =12V

np =1.5

12 x (1−0.45)=0.227

Note : The R1.C1 filteris used to damposcillation

on the secondarysideof thefeedbacktransformer.

The time constant R1 x C1 ≅0.1µs.

III.2.8 - Start up resistor

After switching on the power supply the filtering

capacitor on VCC of TEA2260/61 is charged

through a resistor connected to the mains input

voltage. Do not connect this resistor to the high

voltagefilteringcapacitorbecausethere isenough

energy in this capacitor to cause three attempted

restarts and to cut off the TEA2260/61 on fault

detection when the power supply is switched off.

Hence it is recommended to connect the start-up

resistor as follows :

376-38.EPS

Figure 38

Start up delay time

IMOY =√2xV

IN AC(min)

∏xRST

Start-updelay time = Tst = VCC START

IMOY −ICC START xC

ST =√2xVIN AC(min)

∏x(CxV

CC START

TST )+ I

CC START

Power dissipated in start up resistor

P=VIN AC(max)2

2.R

Numericalapplication

with :

start up delay time = 1s

VIN(max) = 370V DC (VIN AC(max) = 265V)

VIN AC(min) = 175V

Vccstart = 10.3V

Iccstart = 0.7mA

C =220µF

RST =2x175

∏x(220 10−6x 10.3 +0.7 10−3)=26kΩ

Value choosen = 22kΩ

Powerdissipated

P=(265)2

2x22 103=1.6W

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III.2.9 - Determination of high voltage filtering capacitor

376-39A.EPS/ 376-39B.EPS

Figure39

Hypothesis :

∆V : rippleon the filtering voltage

VIN.AC(min) : minimal value of A.C. input voltage

T : periodof the mainsvoltage

Pout :output power of the powersupply

η: efficiency of the power supply

C=T

2πx

2+ArcSin(1−∆V

VIN AC(min)x√2)

∆VIN AC(min)x√2xPOUT

Numericalapplication

∆V =40V

VIN AC(min) = 170 VAC

T = 20ms

POUT = 120W

η= 0.85

C=20 10−3

2πx

2+ArcSin(1−40

250)

40 x 250 x120

0.85 =115µF

value choosen : C = 120µs

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III.3 - ElectricalDiagram

Power primary ground

Secondaryground(isolatedfrom mains)

Small signal secondary ground

170VAC

270 VAC

4 x 1N4007

120µF

385V

BY218-600

PLR811

BY218-100

470µF

25V

1000µF

25V

1000µF

25V

220µF

25V

BA157

1N4148

100pF

2.7nF

1kV

BY299

47µF

BZX85-3V0

2.2µH

220

nF 220

1nF

2.2µF

16V

SGSF

344

313

717

12V

135V

7.5V

Stand-by

control

47nF

1.2

1N4148 150pF Sync.

input

10µF

16V

1873

2465

7645

12 13 16 15

11 10 298314 1

BC547C

3.3nF

TEA2260/61

Ω

120k

Ω

2.2k

Ω

10k

Ω

ΩΩ105k

1% 6.8k

Ω

560k

Ω

0.170 /1W

Ω

22k

100k

100

Ω

22k

Ω1k

Ω

18k

4.7k

OUT

2.2 /0.5W

47kΩ

P : 120W

f : 16kHz

25V

270

TEA5170

100µF

250V

330 Ω

376-40.EPS

Figure40

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IV - TV APPLICATION 140W- 220 VAC - 32kHz

SYNCHRONIZABLE

All detailsconcerningthe determinationof external

componentsare described in section III.

IV.1 - Application Characteristics

- Discontinuousmode flybackSMPS

- Stand-by function using the burst mode of TEA

2260.

- Switchingfrequencyin burstmode : 16kHz

- Switchingfrequencyin normalmode: 32kHz

- Nominal mains voltage : 220VAC

- Mains voltage range: 170 VAC to 270VAC

- Output power range in normal mode 25W < Po

140W

- Outputpower range in stand-by mode 2W < Po

45W

- Efficiencyat full load > 80%

- Efficiencyin stand-bymode (Po = 7W) > 50%

- Short circuit protection

- Longduration overload protection

- Complete shut down after 3 restarts with fault

detectionfor TEA2260

- Complete shut down when VC2 reaches2.6V for

TEA2261

Load regulation

(VDC= 310V)

Output 135V (+/- 0.18%) →(I135 : 0.01A to 0.8A;

I25 =1A)

Output 25V (+/- 2%) →(I135 : O.8A; I25 = 0.5A to

1A)

Line regulation

(I135 : 0.8A; I25 : 1A)

Output135V (+/- 0.13%)→(210V< VDC < 370V)

Output 25V (+/- 0.17%)

IV.2 - Transformer Specification

- Reference: OREGA.SMT5.G4576-03

- ElectricalData :

Winding Pin Inductance

nP3-6 790µH

nAUX 7-9 5.4µH

n2 19-13 338µH

n3 19-20 4.8µH

n4 14-17 3.4µH

n5 22-21 13µH

376-41.EPS

Figure 41

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IV.3 - ElectricalDiagram

Power primary ground

Secondary ground (isolated from mains)

Smallsignal secondary ground

170 VAC

270 VAC

4x 1N4007 BY218-600

PLR811

BY218-100

470µF

25V

1000µF

25V

1000µF

25V

BA157

1N4148

100pF

2.7nF

1kV

BY299

47µF

BZX85-3V0

2.2µH

1nF

2.2µF

16V

SGSF

344

313

717

Stand-by

control

47nF

1N4148 150pF Sync.

input

10µF

16V

187

2465

7645

12 13 16 15

11 10 298314 1

BC547C

TEA2260/61

TEA5170

Ω

120k

Ω

2.2k

Ω

10k

Ω

ΩΩ6.8k

ΩΩ

Ω

22k

100

Ω

4.7k

OUT

2.2 /0.5W

47kΩ

135V

0.8A

7.5V

12V

0.5A

25V

1.2nF

560

100k

220

16W

0.135 /1W

330

22k

3.3

150µF

385V 22k

330µF

25V

P : 140W

f : 32kHz

82k

270

100µF

250V

330Ω

376-42.EPS

Figure42

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V - TV APPLICATION 110W-220 VAC - 40kHz

REGULATED WITH OPTOCOUPLER

This application worksin asynchronousmode. The

regulation characteristics are very attractive (out-

put powervariation range from 1W to 110W due to

automatic burst mode (see II.6). In this configura-

tion higher is the regulationloop gain, lower is the

output voltage ripple in burst mode (e.g. ouput

voltage ripple0.8% with a loop gain of 15).

V.1 - Frequency Soft Start

The nominalswitchingfrequencyis40kHzbut dur-

ing the start-up phase the switching frequency is

shiftedto10kHzinordertoavoidthemagnetization

of the transformer.

Otherwise the second current limitation will be

reachedathighinput voltage and hencethepower

supply will not start.

V.2 - Application Characteristics

- Discontinousmode Flyback SMPS

- Switchingfrequency: 40kHz

- Nominal mains voltage : 220VAC

- Mains voltage range: 170 VAC to 220VAC

- Outputpowerin normalmode : 30W<Po <110W

- Output power in burst mode :

1W < Po < 30W.The transient phase between

normal mode and burst mode is determinated

automaticallyas a function of the output power.

Hence the regulation of the output voltage is

effective for an output power variation of

1W < Po < 110W

- Efficiencyas full load > 80%

- Efficiencyin burstmode (Po = 8W) > 50%

- Short circuit protection

- Open load protection

- Longduration overload protection

- Complete shutdown after 3 restarts with fault

detectionfor TEA2260

- Complete shut down when VC2 reaches2.6V for

TEA2261

Load regulation (VDC = 310V)

Output 135V (+/- 0.15%) →(I135 : 0.05Ato 0.6A;

I25 = 1A)

Output 25V (+/- 2.5%) →(I135 = 0.6A; I25 : 0.25 to

1A)

Line regulation (I

135

: 0.6A;I

25 :

1A)

Output135V(+/- 0.30%) →(210V< VDC <, 370V)

Output 25V (+/- 0.30%)

Influence of the audio output on the video out-

put

Output135V(+/- 0.1%) →(I135 =0.6A;I25 :0→1A)

Output135V(+/-0.05%)→(I135 =0.3A;I25 :0→1A

V.3 - TransformerSpecification

- Reference: OREGA.SMT5.G4576-02

- MechanicalData :

- Ferrite : B50

- 2 cores: 53 x 18 x 18(mm) THOMSON LCC

- ElectricalData :

Winding Pin Inductance

nP3-6 790µH

nAUX 7-9 5.4µH

n2 19-13 338µH

n3 19-20 4.8µH

n4 14-17 3.4µH

n5 22-21 13µH

376-43.EPS

Figure 43

HIGH PERFORMANCE DRIVER CIRCUITSFOR S.M.P.S

32/33

V.4 - ElectricalDiagram

Power primary ground

Secondaryground(isolatedfrommains)

Smallsignal secondaryground

170 VAC

270 VAC

4 x 1N4007 BY218-600

PLR811

BY218-100

470µF

25V

BA157

2.7nF

1kV

BY299

47µF

BZX85-3V0

2.2µHSGSF

344

313

717

764512 13 16 15

11 10 2983

14 1

TEA2260/61

Ω120k

Ω

100

Ω

OUT

2.2 /0.5W

25V

220

16W

330µF

25V

135V

0.7A

12V

0.5A

nF 560

2.2k

120µF

385V 22k

1µF1µF

680

Ω220k

Ω56k

2.2M

BC547

nF 0.120 /1W

4.7k

Ω

4.7k

7.5V

BC547A

CNX62

2.2

BZX55C6V2

10nF

470µF

25V

470µF

40V

P : 110W

f :40kHz

100µF

250V

330 Ω

376-44.EPS

Figure44

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33/33

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