ST AN2509 Application note

AN2509

Application note

Wide range 400W (+200 V@1.6 A / +75 V@1 A)

L6599-based HB LLC resonant converter

Introduction

This note describes the performances of a 400W reference board, with wide-range mains operation and power-factor-correction (PFC) and presents the results of its bench evaluation. The electrical specification refers to a power supply for general purpose application, with two main output voltages (200 V and 75 V).

The main features of this design are the very low no-load input consumption (<0.5 W) and the very high global efficiency, better than 90% at full load and n ominal mains v o ltage (115 230 V

The circuit consists of three main bloc ks. The first is a front-end PFC pre-re gulator based on the L6563 PFC controller. The second stage is a multi-resonant half-bridge converter with two output volta ges of +200 V/300 W a nd 75 V/75 W, whose control is implemented through the L6599 resonant controller. A further auxiliary flyback converter based on the VIPer12A off-line primary switcher completes the architecture. This third block, deliv ering a total power of 7 W on two output voltages (+3.3 V and +5 V), is mainly intended for microprocessor supply and display power management operations

L6599 & L6563 400W demonstration board

April 2007 Rev 3 1/37

www.st.com

Contents AN2509

Contents

1 Main characteristics and circuit description . . . . . . . . . . . . . . . . . . . . . 4

2 Electrical test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.1 Harmonic content measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.2 Efficiency measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.3 Resonant stage operating waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.4 Standby and no-load power consumption . . . . . . . . . . . . . . . . . . . . . . . . 17

2.5 Short-circuit protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.6 Overvoltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

3 Thermal tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

4 Conducted emission pre-compliance test . . . . . . . . . . . . . . . . . . . . . . 21

5 Bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

6 PFC coil specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

6.1 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

6.2 Mechanical aspect and pin numbering . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

7 Resonant power transformer specification . . . . . . . . . . . . . . . . . . . . . 30

7.1 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

8 Auxiliary flyback power transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

8.1 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

9 Board layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

10 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

11 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

2/37

AN2509 List of figures

List of figures

Figure 1. PFC pre-regulator electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Figure 2. Resonant converter electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Figure 3. Auxiliary converter electrical diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Figure 4. Compliance to EN61000-3-2 standard for harmonic reduction: full load . . . . . . . . . . . . . . . 9

Figure 5. Compliance to EN61000-3-2 standard for harmonic reduction: 70 W load. . . . . . . . . . . . . . 9

Figure 6. Compliance to JEIDA-MITI standard for harmonic reduction: full load . . . . . . . . . . . . . . . . . 9

Figure 7. Compliance to JEIDA-MITI standard for harmonic reduction: 70 W load . . . . . . . . . . . . . . . 9

Figure 8. Power factor vs. Vin & load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 9. Total harmonic distortion vs. Vin & load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 10. Overall efficiency versus output power at nominal mains voltages. . . . . . . . . . . . . . . . . . . 12

Figure 11. Overall efficiency versus input mains voltage at various output power levels . . . . . . . . . . 12

Figure 12. Resonant circuit primary side waveforms at full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 13. Resonant circuit primary side waveforms at light load (about 45 W output power) . . . . . . 14

Figure 14. Resonant circuit primary side waveforms at no load condition. . . . . . . . . . . . . . . . . . . . . . 14

Figure 15. Resonant circuit secondary side waveforms: +200 V output . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 16. Resonant circuit secondary side waveforms: +75 V output . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 17. Low frequency (100 Hz) ripple voltage on +200 V and + 75 V outputs . . . . . . . . . . . . . . . 16

Figure 18. Load transition (0.16 A - 1.6 A) on +200 V output voltage . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 19. +200 V output short-circuit waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Figure 20. Thermal map @115 V Figure 21. Thermal map at 230 V Figure 22. Peak measurement on LINE at 115 V Figure 23. Peak measurement on Neutral at 115 V Figure 24. Peak measurement on LINE at 230 V Figure 25. Peak measurement on Neutral at 230 V

Figure 26. Electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Figure 27. Pin side view. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Figure 28. Electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Figure 29. Mechanical aspect and pin numbering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Figure 30. Winding position on coil former. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Figure 31. Electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Figure 32. Auxiliary transformer winding position on coil former . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Figure 33. Copper tracks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Figure 34. Thru-hole component placing and top silk screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Figure 35. SMT component placing and bottom silk screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

- full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

- full load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

and full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

and full load. . . . . . . . . . . . . . . . . . . . . . . . . . . 21

and full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

and full load. . . . . . . . . . . . . . . . . . . . . . . . . . . 22

3/37

Main characteristics and circuit description AN2509

1 Main characteristics and circuit description

● The main characteristics of the SMPS are listed below:

● Universal input mains range: 90 to 264 V

● Output voltages: 200 V @ 1.5 A - 75 V @ 1 A - 3.3 V @ 0.7 A - 5 V @ 1 A

● Mains harmonics: compliance with EN61000-3-2 specifications

● Standby mains consumption: less than 0.5 W @230 V

●

Overall efficiency: better than 87% at full load, 90-264 V

●

EMI: Compliance with EN55022-class B specifications

● Safety: Compliance with EN60950 specifications

● PCB single layer: 132x265 mm, mixed PTH/SMT technologies

The circuit consists of three stages. A front-end PFC pre-regulator implemented by the controller L6563 (Figure 1), a half-bridge resonant DC/DC conve rter based on the reson ant controller L6599 (Figure 2), and a 7 W flyback converter intended for standby management (Figure 3) utilizing the VIPer12A off-line primary switcher.

The PFC stage delivers a stable 400 VDC supply to the do wnstream con v erters (resonant + flyback) and provides for the reduction of the current harmonics drawn from the mains, in order to meet the requirements of the Euro pe a n no rm EN61000-3-2 and the JEIDA-MITI norm for Japan.

- 45 to 65 Hz:

The PFC controller is the L6563 (U1), integrating all functions needed to operate the PFC and interface the downstream resonant converter. Although this controller chip is designed for Transition-Mode (TM) operation, where the boost inductor wo rks next to the boundary between Continuous (CCM) and Discontin uous Conduction Mode (DCM), by adding a simple external circuit, it can be operated in LM-FOT (line-modulated fixed off-time). This mode allows for CCM o perat ion, normally achie v ab le with more e x pensiv e contro l chips and more complex architectures . The LM-F O T mode allows the use of a lo w-cost de vice lik e the L6563 at a high power level, usually covered by CCM topologies. For a detailed and complete description of the LM-FOT operating mode see the application note AN1792. The external components to configure the circuit in LM-FOT mode are: C15, C17, D5, Q3, R14, R17 and R29.

The power stage of the PFC is a conventional boost converter, connected to the output of the rectifier bridge through a differential mode filtering cell (C5, C6 and L3) for EMI reduction. It includes a coil (L4), a diode (D3) and two capacitors (C7 and C8). The boost switch consists of two power MOSFETs (Q1 and Q2), connected in parallel, which are directly driven by the L6563 output drive thanks to the high current capability of the IC.

The divider (R30, R31 and R32), connected to MULT pin 3, provides the information of the instantaneous voltage that is used to modulate the boost current and to derive further information like the average value of the AC line used by the V

(voltage feed-forward)

function. This function is used to keep the output voltage almost independent of the mains. The divider (R3, R6, R8, R10 and R11) is dedicated to detecting the output voltage while a further divider (R5, R7, R9, R16 and R25) is used to protect the circuit in case of voltage loop failure.

The second stage is an LLC resonant converter, with half-bridge topology implementation, working in ZVS (zero voltage switching) mode.

4/37

AN2509 Main characteristics and circuit description

The controller is the L6599 integrated circuit that incorporates the necessary functions to properly drive the two half-bridge MOSFETs b y a 50 % fix ed duty cycle with fixed dead-time, changing the frequency according to the feedback signal in order to regulate the output voltages against load and input voltage variations. The main features of the L6599 are a non-linear soft-start, a current protection mode used to program the hiccup mode timing, a dedicated pin for sequencing or brown-out (LINE) and a standby pin (STBY) for burst mode operation at light loads (not used in this design).

The transformer (T1) uses the magne tic integration approach, incorporating the resonant series and shunt inductances of the LLC resonant tank. Thus, no additional external coils are needed for the r esonance. F or a detaile d analysis of the LLC r esonant con v erter , please refer to the application note AN2450.

The secondary side power circuit is configured with center- tap windings and two diodes rectification for each outpu t (diod es D8A, D8B, D10A, D10B). The two center tap windings are connected in series on the DC side (r efer to Figure 2). The +75 V rail is connected to the center tap of the higher voltage winding (the one connected to the anodes of D8A and D8B diodes). Therefore the higher v oltage windin g only has to provide a v oltage equal to the difference of the two output voltages: 200 V - 75 V = 125 V. This winding arrangement has the advantage of a better cross regulation with respect to the case of two completely separated outputs. F urthermore, due to the fact that the +200 V diodes only have to withstand a voltage of about 25 0 V (2 x 125 V), inst ead of about 400 V in case of complet ely separated windings, the designer can select a diode with a lower junction capacitance minimizing the effect of this capacitance refle ct ed at transformer primary side. This may affect the behavior of the resonant tank, changing the circuit from LLC to LLCC type, with the risk that the conv erter, in light-load/n o-load condition ( when the f e edbac k loop increa ses the operating frequency), can no longer control the output voltage.

The feedbac k loop is implemented b y means of a classical con figuration using a TL431 (U4) to adjust the current in the optocoupler diode (U3). The optocoupler transistor modu lates the current from controller Pin 4, so the frequency will change accordingly, thus achieving the output voltage regulation. Resistors R46 and R54 set the maximum operat ing frequency.

In case of a short circuit, the current entering the primary winding is detected by the lossless circuit (C34, C39, D11, D12, R43, and R45) and the resulting signal is fed into L6599 Pin 6. In case of overload, the voltage on Pin 6 exceeds an internal threshold that triggers a protection sequence via Pin 2, keeping the current flowing in the circuit at a safe level.

The third stage is a small flyback converter based on the VIPer12A, a current mode controller with integrated power MOSFET, capable of delivering about 7 W total output power on the output voltages (5 V and 3.3 V). The regulated output voltage is the 3.3V output and, also in this case, the feedback loop uses the TL431 (U7) and optocoupler (U6) to control the output volta ge.

This converter is able to operate in the whole mains voltage range, even when the PFC stage is not working. From the auxiliary winding on the primary side of the flyback transformer (T2), a voltage Vs is available, intended to supply the other controllers (L6563 and L6599) in addition to the VIPer12A itself.

The PFC stage and the resonant converter can be switched on and off through the circuit based mainly on components Q7, Q8, D22 and U8, which, depending on the level of the signal ST-BY, supplies or removes the auxiliary voltage (VAUX) necessary to start-up the controllers of the PFC and resonant stages. When the AC input voltage is applied to the power supply, the small flyback converter switches on first. Then, when the ST-BY signal is asserted low, the PFC p re-regulator becomes oper ative , and last the resonant conv erter can deliver the output power to the load. Note that if Pin 9 of Connector J3 is left floati ng (no

5/37

Main characteristics and circuit description AN2509

signal ST-BY present), the PFC and resonant converter will not operate, and only +5 V and +3.3 V supplies are availa ble on the output. In order to enable the +200 V and +75 V outputs, Pin 9 of Connector J3 must be pulled down to ground.

Figure 1. PFC pre-regulator electrical diagram

Vdc

+400V

2nF2-Y 1

330uF/450V

NTC 2R5-S237

470nF/630V

STTH8R06

1-2

1N5406

PQ40-500uH

5-6

LL4148

STP12NM50FP

LL4148

R18

R15

6R8

R24

0R39

R23

0R39

R22

0R39

R21

0R39

R19

1k0

C18

330pF

Vrect

470nF/630V

DM-51uH-6A

470nF/630V

Vaux

D15XB60

C11

680nF-X2

Jumper

330nF-X2

470nF-X2

1M5

2nF2-Y2

C10

2nF2-Y2

CON2-IN

Jumper

CM-1.5mH-5A

8A/250V

C13

10uF/50V

C12

100nF

680kR8680k

680k

Vdc

2M2

R11

R10

2M2

C15

100pF

R14

3k3

R17

C17

15k

L6563

100k

R13

56k

C14

100nF

C16

1uF

2M2

CSCS

LL4148

15k

220pF

VCC

INV

COMP

ZCD

GND

MULTCSVFF

PWM-Latch

R29

1k5

BC857C

R20

1k0

C21

2nF2

R28

RUN

PWM-STOP

TBO

PFC-OK PWM-LATCH

R16

5k1

LINE

240k

R26

150k

C20

470nF

C19

10nF

R25

30k

C22

10nF

R32

10k

R31

620k

R30

620k

Vrect

6/37

AN2509 Main characteristics and circuit description

Figure 2. Resonant converter electrical diagram

1234567

+200V

CON8

C25

22uF/250V

C29

10uH

C30

D8A

T-RE S-ER 49- 400 W

D8B

BYT08P-400

C28

47nF/630V

+75V

C38

C35

100uF/250V

47uF/100V

22uH

D10B

D10A

STTH1002C

220uF/100V

C37

220uF/100V

R50

56k

R49

56k

R48

56k

R86

C59

R53

C41

D13

R52

470R

47nF

R61

75k

R58

75k

10uF/50V

C-12V

R56

1k0

3k3

U3A

SFH617A-2

2k7

R60

6k2

R59

1k0

C44

47nF

TL431

R43

150

C34

220pF/630V

Vdc

R33

R88

560k

Q12

BC557

C61

470nF

STP14NK50Z

R35

LL4148

C23

100nF

STP14NK50Z

R39

R40

LL4148

C27 100nF

L6599

R36

R34

2k7

C24

470nF

R37

2M2

VBOOT

CSS

C26

OUT

HVG

DELAYCFRFMIN

270pF

R41

Vaux

C32

100nF

R38

C31

10uF/50V

LVG

VCC

STBY

ISEN

LINE GND

DIS PFC-STOP

C33

4nF7

R42

16k

D11

LL4148

D12

LL4148

R45

100R

C39

1uF0

U3B

C40

10nF

R47

10k

R46

1k5

SFH617A-2

R87

220R

C60

470nF

R54

1k5

LINE

PWM-Latch

7/37

Main characteristics and circuit description AN2509

Q10

BC847C

C54

100nF

TL431

C53

2nF2

U6A

SFH617A-2

U6B

SFH617A-2

+200V

R67

1k0

SSFB

Vdd D

VIPER-12A

R82

100k

R79

2k2

D15

1N5822

D16

1N5821

D20

BAV103

C56

100nF

C45

1000uF/10V

C47

1000uF/10V

C50

10uF/50V

C46

100uF/10V

C49

100uF/10V

BC857C

C48

10uF/50V

R76

150k

U8A

SFH617A-2

R75

150k

U8B

SFH617A-2

R74

10k

R77

4k7

D19

C-30V

St-By

D18

B-10V

123456789

CON10

R69

Vdc

C52

47nF

R68

22k

C51

100nF

R71

10k

BC847C

R72

10k

C55

10uF/50V

R66

1k0

T-FLY -AUX-E20

+400V

R70

22R

Vdc

+400V

R83

1M0

R84

150k

C58

10nF

Q11

BC557C

+5Vst -by

R81

30k

R80

30k

+3V3

+5Vst-by

BC547C

D22

C-15V

33uH

D17

LL4148

+75V

D21

B-15V

D23

B-15V

R62

R64

1k6

C57

1nF0

Vaux

+5Vst -by

D14

PKC-136

St-By

R73

8k2

Figure 3. Auxiliary converter electrical diagram

8/37

AN2509 Electrical test results

2 Electrical test results

2.1 Harmonic content measurement

The current harmonics drawn from the mains have been measured according to the European rule EN61000-3-2 Class-D and Japanese rule JEIDA-MITI Class-D, at full load and 70 W output power, at both nominal input voltages (230 V in Figure 4 to Figure 7 show that the measured current harmonics are well below the limits imposed by the regulations , both at full-load and at 70 W load.

and 100 VAC). The graphs

Figure 4. Compliance to EN61000 -3 -2

standard for harmonic reductio n :

0.1

0.01

0.001

0.0001

full load

Measurements @ 230Vac Full load EN61000-3-2 class D limit s

1234567891011121314151617181920

Harmoni c Order (n)

Figure 6. Compliance to JEIDA-MITI standard

for harmonic reduction: full load

Measurements @ 100Vac Full load J EIDA- M ITI c la ss D l im it s

Figure 5. Compliance to EN61000-3-2

standard for harmonic reduction: 70 W load

Measurement s @ 230Vac 70W EN61 000-3-2 cl ass D limits

0.1

0.01

0.001

0.0001 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Harmoni c Order (n)

Figure 7. Compliance to JEIDA-MITI standard

for harmonic reduction: 70 W load

Measurement s @ 100V ac 70W JEI DA -MIT I cla s s D limits

0.1

0.01

0.001

0.0001 1234567891011121314151617181920

Harmoni c Order (n)

The Power Factor (PF) and the Total Harmonic Distortion (THD) are reported in Figure 8 and Figure 9. It is evident from the graph that th e PF stays close to unity in the whole mains voltage range at full load and at half load, while it decreases at high mains at low load (70 W). The THD has similar behavior, remaining within 25% overall the mains voltage range and increasing at low load (70 W) at high mains voltage.

0.1

0.01

0.001

0.0001 1234567891011121314151617181920

Harmoni c Orde r (n )

9/37

Electrical test results AN2509

Figure 8. Power factor vs. Vin & load Figure 9. Total harmonic distortion vs. Vin &

1.00

0.98

0.95

0.93

0.90

0.88

0.85 80 120 160 200 240 280

400W 200W 70W

Vin [Vrms]

THD [%]

25.00

20.00

15.00

10.00

5.00

0.00 80 120 160 200 240 280

load

400W 200W 70W

Vin [Vrms]

2.2 Efficiency measurements

Table 1 and Table 2 show the output voltage measurements at the nominal mains voltages

of 115 V load and at light load operations, the input power is measured using a Yokogawa WT-210 digital power meter. Particular attention has to be paid when measuring input power at full load in order to avoid measurement errors due to the voltage drop on cables and connections.

and 230 VAC, with different load condi tions. For all measurements, both at full

Figure 10 shows the overall circuit efficiency, measured at each load condition, at both

nominal input mains voltages of 115 V

and 230 VAC. The values were measured af ter 30

minutes of warm-up at maximum load. The high efficiency of the PFC pre-regulator working in FOT mode and the very high efficiency of the resonant stage working in ZVS (i.e. with negligible switching losses), provides for an overall efficiency better than 87% at full load in the complete mains voltag e r a ng e. This is a significant high value for a two-stage converter , especially at low input mains voltage where the PFC conduction losses increase. Even at lower loads, the efficiency still remains high.

Table 1. Efficiency measurements @VIN = 115 V

+200 V @load(A) +75 V@load(A) +5 V @load(A) +3.3 V@load(A) POUT(W) PIN(W) Eff. %

200.29 1.591 77.77 1.020 4.88 0.975 3.33 0.695 405.06 433.30 93.48%

200.29 1.441 77.78 0.894 4.88 0.975 3.33 0.695 365.23 390.68 93.48%

200.31 1.281 77.78 0.801 4.88 0.975 3.33 0.695 325.97 348.98 93.41%

200.31 1.120 77.79 0.694 4.88 0.975 3.33 0.695 285.41 306.05 93.25%

200.32 0.962 77.79 0.600 4.88 0.502 3.33 0.352 243.00 260.90 93.14%

200.34 0.802 77.80 0.506 4.88 0.502 3.33 0.352 203.66 219.52 92.78%

200.34 0.642 77.80 0.399 4.88 0.502 3.33 0.352 163.28 177.37 92.06%

200.34 0.481 77.81 0.306 4.88 0.502 3.33 0.352 123.80 136.39 90.77%

200.40 0.321 77.83 0.199 4.86 0.144 3.33 0.097 80.84 91.34 88.50%

200.43 0.161 77.83 0.105 4.86 0.146 3.33 0.099 41.48 50.48 82.17%

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AN2509 Electrical test results

Table 2. Efficiency measurements @V

+200 V @load(A) +75 V @load(A) +5 V @load(A) +3.3 V @load(A) POUT(W) PIN(W) Eff. %

200.32 1.593 77.78 1.022 4.88 0.977 3.33 0.695 405.68 449.65 90.22%

200.32 1.442 77.79 0.896 4.88 0.977 3.33 0.695 365.64 404.46 90.40%

200.32 1.282 77.80 0.802 4.88 0.977 3.33 0.695 326.29 360.10 90.61%

200.32 1.120 77.80 0.694 4.88 0.977 3.33 0.695 285.43 314.90 90.64%

200.35 0.962 77.80 0.600 4.88 0.502 3.33 0.351 243.04 267.18 90.96%

200.32 0.802 77.79 0.508 4.88 0.502 3.33 0.351 203.79 224.33 90.84%

200.31 0.641 77.79 0.399 4.88 0.503 3.33 0.351 163.06 180.53 90.32%

200.34 0.480 77.80 0.305 4.88 0.503 3.33 0.351 123.52 138.06 89.47%

200.40 0.321 77.83 0.197 4.86 0.144 3.33 0.097 80.68 91.83 87.86%

200.43 0.160 77.84 0.050 4.86 0.146 3.33 0.099 405.68 49.72 74.42%

= 230 V

The global efficiency at full load has been measured even at the limits of the input voltage range, with good results:

At VIN = 90 V At VIN = 264 V

- full load, the efficiency is 87.27%

- full load, the efficiency is 93.49%

Also at light load, at an output power of about 10% of the maximum level, the overall efficiency is very good, reaching a v alue of about 75% a t nominal main s v oltag es. Figure 11 shows the efficiency measured at various output power levels versus input mains voltage.

The cross regulation of the resonant converter stage is very good as shown in Table 3, where the +200 V and +75 V output v o ltages are measur ed in different load conditions, with minimum output current equa l to 10% of maximum current for both the output volta ges.

Table 3. Cross regulation

230 V

200 V load 75 V load 200 V 75 V 200 V 75 V

max max 200.26 77.77 200.32 77.78 max min 200.35 77.92 200.35 77.94

min max 200.35 77.58 200.35 77.58 min min 200.42 77.82 200.45 77.84

no-load no-load 200.76 77.66 200.76 77.65

115 V

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Electrical test results AN2509

Figure 10. Overall efficiency versus output power at nominal mains voltages

230Vac 115Vac

95%

90%

85%

Eff. (%)

80%

75%

70%

0 50 100 150 200 250 300 350 400 450

Output Power (W)

Figure 11. Overall efficiency versus input mains voltage at various output power

levels

400W 200W 70W

Eff[%]

94% 93% 92% 91% 90% 89% 88% 87% 86% 85%

80 120 160 200 240 280

Vin [Vrms]

2.3 Resonant stage operating waveforms

Figure 12 shows some waveforms during steady state operation of the resonant circuit at full

load. The Ch1 waveform is the half-bridge square voltage on Pin 14 of L6599, driving the resonant circuit. In the picture it is not e vident, but the switching frequency is normally slightly modulated following the PFC pre-regulator 100-Hz ripple that is rejected by the

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