ST AN2393 Application note

AN2393

Application note

Reference design: wide range 200W L6599-based

HB LLC resonant converter for LCD TV & flat panels

Introduction

This note describes the performances of a 200 W reference board, with wide-range mains operation and power-factor-correction (PFC). Its electrical specification is tailored to a typical high-end application for LCD TV or monitor applications.

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 87% at full load and nominal mains voltage (115 230 V

The circuit consists of three main blocks; the first is a front-end PFC pre-regulator based on the L6563 PFC controller. The second stage is a multi-resonant half-bridge converter whose control is implemented through the STMicroelectronics L6599 resonant controller. A further auxiliary flyback converter based on the VIPer12A-E off-line primary switcher completes the architecture. This third block is mainly intended for microprocessor supply and display power management operations.

Figure 1. L6599 and L6563 200W evaluation board (EVAL6599-200W)

October 2007 Rev 5 1/35

www.st.com

Contents AN2393

Contents

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

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

2.1 Efficiency measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.2 Resonant stage operating waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.3 Stand-by and no load power consumption . . . . . . . . . . . . . . . . . . . . . . . . 14

2.4 Short-circuit protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.5 Overvoltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3 Thermal tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

4 Conducted emission pre-compliance test . . . . . . . . . . . . . . . . . . . . . . 20

5 Bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

6 PFC coil specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

6.1 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

6.2 Mechanical aspect and pin numbering . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

7 Resonant power transformer specification . . . . . . . . . . . . . . . . . . . . . 27

7.1 Electrical characteristics and mechanical aspect . . . . . . . . . . . . . . . . . . . 28

8 Auxiliary flyback power transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

8.1 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

9 Reference design board layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

10 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

2/35

AN2393 List of figures

List of figures

Figure 1. L6599 and L6563 200W evaluation board (EVAL6599-200W). . . . . . . . . . . . . . . . . . . . . . . 1

Figure 2. PFC pre-regulator electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Figure 3. Resonant converter electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Figure 4. Auxiliary converter electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Figure 5. Overall efficiency versus output power at nominal mains voltages. . . . . . . . . . . . . . . . . . . 10

Figure 6. Overall efficiency versus output power at several input voltage values . . . . . . . . . . . . . . . 11

Figure 7. Resonant circuit primary side waveforms at full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Figure 8. Resonant circuit primary side waveforms at no-load condition. . . . . . . . . . . . . . . . . . . . . . 12

Figure 9. Resonant circuit secondary side waveforms: +24 V output . . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 10. Resonant circuit secondary side waveforms: +12 V output . . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 11. Low frequency (100 Hz) ripple voltage on the output voltages . . . . . . . . . . . . . . . . . . . . . . 13

Figure 12. Load transition (0 - 100%) on +24 V output voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Figure 13. Load transition (0 - 100%) on +12 V output voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Figure 14. +24 V output short-circuit waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 15. +12 V output short-circuit waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 16. Thermal map @115 V Figure 17. Thermal map at 230 V Figure 18. CE quasi peak measurement at 115 V Figure 19. CE quasi peak measurement at 230 V

Figure 20. PFC coil electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Figure 21. PFC coil pin side view. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Figure 22. Mechanical aspect and pin numbering of resonant transformer . . . . . . . . . . . . . . . . . . . . . 28

Figure 23. Resonant transformer electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Figure 24. Resonant transformer winding position on coil former . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Figure 25. Auxiliary transformer electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Figure 26. Auxiliary transformer winding position on coil former . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Figure 27. Copper tracks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Figure 28. Thru-hole component placing and top silk screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Figure 29. SMT component placing and bottom silk screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

- full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

and full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

3/35

Main characteristics and circuit description AN2393

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:

– 24 V@6 A continuous operation

– 12 V@ 5 A continuous operation

– 3.3 V@ 0.7 A continuous operation

– 5 V@ 1 A continuous operation

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

● St-by mains consumption: Typical 0.5 W @230 V

●

Overall efficiency: better than 88% at full load

● 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 2), a half-bridge resonant DC/DC converter based on the resonant controller L6599 (Figure 3) and a 7 W flyback converter intended for stand-by management (Figure 4) utilizing the VIPer12A-E off-line primary switcher.

and frequencies between 45 and 65 Hz

The PFC stage delivers a stable 400 V

supply and provides for the reduction of the mains

harmonics, in order to meet the requirements of the European norm EN61000-3-2 and the JEIDA-MITI norm for Japan.

The PFC controller is the L6563 (U1), working in FOT (fixed off-time) mode and integrating all functions needed to operate the PFC and interface the downstream resonant converter.

Note: The FOT control is implemented through components C15, C17, D5, Q3, R14, R17 and R29

(see AN1792 for a complete description of a FOT PFC pre-regulator).

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), diode (D3) and two capacitors (C7 and C8).

The boost switch is represented by the Power MOSFET (Q2) which is directly driven by the L6563 output drive thanks to the high current capability of the IC.

The divider (R30, R31 and R32) provides the L6563 (MULT Pin 3) with the information of the instantaneous voltage that is used to modulate the boost current and to derive some 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 one.

The first divider (R3, R6, R8, R10 and R11) is dedicated to detecting the output voltage while the second divider (R5, R7, R9, R16 and R25) is used to protect the circuit in case of voltage loop fail.

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

The controller is the L6599 integrated circuit that incorporates the necessary functions to drive properly the two half-bridge MOSFETs by a 50 percent fixed duty cycle with dead-time,

4/35

AN2393 Main characteristics and circuit description

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 stand-by pin (STBY) for burst mode operation at light loads (not used in this design).

The transformer uses the magnetic integration approach, incorporating the resonant series and shunt inductances. Thus, no additional external coils are needed for the resonance. The transformer configuration chosen for the secondary winding is center-tap, and the output rectifiers are Schottky type diodes, in order to limit the power dissipation. The feedback loop is implemented by means of a classical configuration using a TL431 (U4) to adjust the current in the optocoupler diode (U3). A weighted resistive divider (R53, R57, R58, R60 and R61) is used to detect both output voltages in order to get a better overall voltage regulation. The optocoupler transistor modulates the current from Pin 4, so the frequency will change accordingly, thus achieving the output voltage regulation. Resistors R46 and R54 set the maximum operating 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 Pin 6.

In case of overload, the voltage on Pin 6 will overpass 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-E, a current mode controller with integrated Power MOSFET, capable of delivering (approximately) 7 W output power on the output voltages (5 V and 3.3 V). The regulated output voltage is the 3.3 V output and, also in this case, the feedback loop bases on the TL431 (U7) and optocoupler (U6) to control the output voltage.

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-E 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 (V

) necessary to start-up the

AUX

controllers of the PFC and resonant stages. In this way, 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 low, the PFC pre-regulator becomes operative, and last the resonant converter can deliver the output power to the load.

Note that if Pin 9 of Connector J3 is left floating (no signal ST-BY present), the PFC and resonant converter will be not operating, and only +5V and +3.3V supplies are available on the output. In order to enable the +24 V and +12 V outputs, Pin 9 of Connector J3 must be pulled down to ground.

5/35

Main characteristics and circuit description AN2393

Figure 2. PFC pre-regulator electrical diagram

Vdc

+400V

2nF2-Y1

220uF/450V

NTC 2R5-S237

470nF/630V

STTH8R06

1-2

1N5406

PQ35-900uH

4-5

STP12NM50FP

LL4148

R18

6R8

R24

0R68

R23

0R68

R22

0R68

R21

2R2

R19

C18

330pF

Vrect

680nF/630V

DM-LSR-72uH-3A

330nF/630V

Vaux

D15XB60

C11

Jumper

CM-TF2628V-5mH-3A

6.3A/250V

2nF2-Y2

680nF-X2

C10

2nF2-Y2

Jumper

330nF-X2

100nF-X2

1M5

CON2-IN

C13

10uF/50V

C12

100nF

680kR8680k

680k

Vdc

2M2

R11

R10

2M2

C15

100pF

R14

1k5

R17

C17

15k

L6563

100k

R13

56k

C14

100nF

C16

1uF

2M2

LL4148

15k

220pF

CSCS

PWM-Latch

R29

1k5

BC857C

R20

1k0

C21

2nF2

R28

ZCD

VCC

RUN

GND

PWM-STOP

INV

COMP

MULTCSVFF

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

6/35

AN2393 Main characteristics and circuit description

Figure 3. Resonant converter electrical diagram

1234567

+24V

CON8

C25

470uF/35V

C30

+12V

R61

R53

33k

R58

R51

2k2

R57

C38

C35

2200uF/35V

470uF/25V

2200uF/25V

15k

3k9

R60

3k9

2uH2

D8A

Vdc

R33

D8B

STPS20H100CF

R35

LL4148

STPS20H100CF

T-RE S-ER4 9

C28

22nF/630V

STP14NK50Z

R39

R40

LL4148

C29

2200uF/35V

2uH2

D10A

STPS20L40CF

Vaux

R38

C37

2200uF/25V

D10B

STPS20L40CF

91011

R43

150

C34

220pF/630V

C32

100nF

C31

10uF/50V

D11

LL4148

D12

LL4148

R45

75R

C39

220nF

C41

10uF/50V

D13

C-12V

R59

R56

1k0

R52

5k6

U3A

SFH617A-2

27k

C44

47nF

TL431

C27 100nF

LVG

OUT

VCC

HVG

VBOOT

L6599

CSS

DELAYCFRFMIN

STBY

ISEN

LINE GND

CC by rework

16k

DIS PFC-STOP

C33

4nF7

R42

LINE

R36

R34

2k7

C23

2uF2

C24

470nF

C26

270pF

R37

1M0

R41

C40

10nF

R47

10k

R46

5k6

PWM-Latch

U3B

SFH617A-2

R54

5k6

7/35

Main characteristics and circuit description AN2393

Q10

BC847C

C54

100nF

TL431

C53

2nF2

U6A

SFH617A-2

U6B

SFH617A-2

+24V

R67

1k0

SSFB

Vdd D

VIPER-12A

R82

1k5

R79

1k0

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

1k5

U8A

SFH617A-2

R75

U8B

SFH617A-2

Vdc

R74

10k

R77

4k7

D19

C-30V

St-By

D18

B-10V

+400V

C57

1nF0

R69

Vdc

C52

47nF

R68

22k

C51

100nF

R71

10k

9 - 10

R83

1M0

BC847C

R84

150k

R72

10k

C55

10uF/50V

R66

1k0

C58

10nF

T-FLY-AUX-E20

+400V

Q11

BC557C

R70

22R

+5Vst-by

+3V3

+5Vst-by

BC547C

D22

C-15V

33uH

D17

LL4148

123456789

CON10

+12V

D21

B-27V

D23

B-15V

R62

R64

1k6

Vaux

+5Vst-by

D14

PKC-136

St-By

R73

8k2

Figure 4. Auxiliary converter electrical diagram

8/35

AN2393 Electrical test results

2 Electrical test results

2.1 Efficiency measurements

Ta bl e 1 and Tabl e 2 show the output voltage measurements at the nominal mains voltages

of 115 V and at light load operation, 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. Therefore please connect the WT210 voltmeter termination to the board input connector. For the same reason please measure the output voltage at the output connector or use the remote sense option of your active load for a correct output voltage measurement.

Table 1. Efficiency measurements @

+24 V(V) @load(A) +12 V(V) @load(A) +5 V(V) @load(A) +3.3 V(V) @load(A) P

23.81 - 6.00 11.86 - 4.94 4.93 - 0.98 3.35 - 0.71 208.66 235.00 88.79%

24.04 - 3.04 11.80 - 4.91 4.93 - 0.98 3.35 - 0.71 138.23 155.50 88.89%

23.84 - 3.02 11.91 - 1.98 4.93 - 0.98 3.35 - 0.71 102.79 115.47 89.02%

and 230 Vac, with different load conditions. For all measurements, both at full load

VIN = 115 V

(W) PIN (W) Efficiency

OUT

23.79 - 2.01 11.96 - 0.49 4.96 - 0.31 3.35 - 0.31 56.25 63.55 88.52%

23.94 - 0.53 11.92 - 0.49 4.97 - 0.31 3.35 - 0.31 21.11 25.56 82.58%

Table 2. Efficiency measurements @V

+24 V(V) @load(A) +12 V(V) @load(A) +5 V(V) @load(A) +3.3 V(V) @load(A) P

23.82 - 6.00 11.86 - 4.94 4.94 - 0.98 3.35 - 0.71 208.73 229.96 90.77%

24.05 - 3.04 11.80 - 4.91 4.94 - 0.98 3.35 - 0.71 138.27 152.85 90.46%

23.85 - 3.02 11.91 - 1.98 4.94 - 0.98 3.35 - 0.71 102.83 114.05 90.16%

23.80 - 2.01 11.96 - 0.49 4.96 - 0.31 3.35 - 0.31 56.27 63.47 88.66%

23.94 - 0.53 11.92 - 0.49 4.96 - 0.31 3.35 - 0.31 21.11 26.47 79.73%

= 230 V

(W) PIN (W) Efficiency

OUT

In Ta bl e 1 , Table 2 and Figure 5 the overall circuit efficiency is measured at each load condition, at both nominal input mains voltages of 115 V

and 230 Vac. The values were

measured after 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 88%. This is a significant high value for a two-stage converter with two output voltages delivering an output current in excess of 5 amps, especially at low input mains voltage where the PFC conduction losses increase. Even at lower loads, the efficiency still remains high.

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

● At V

= 90 Vac - full load, the efficiency is 86.88% (P

= 264 Vac - full load, the efficiency is 90.90% (P

= 208.8 W and PIN = 240.3 W)

OUT

= 208.7 W and PIN =

OUT

229.6 W)

9/35

Electrical test results AN2393

Also at light load, at an output power of about 10% of the maximum level, the overall efficiency is very good, reaching a value better than 79% over the entire input mains voltage range.

Figure 6 shows the efficiency measured at various input voltages versus output power.

Figure 5. Overall efficiency versus output power at nominal mains voltages

95.00%

94.00%

93.00%

92.00%

91.00%

90.00%

89.00%

88.00%

87.00%

86.00%

85.00%

84.00%

efficiency (

83.00%

82.00%

81.00%

80.00%

79.00%

78.00%

77.00%

76.00%

75.00% 0 102030405060708090100110120130140150160170180190200210

Output power (W)

eff% @ 115 V a c eff% @ 230 V a c

10/35

AN2393 Electrical test results

Figure 6. Overall efficiency versus output power at several input voltage values

95.00%

94.00%

93.00%

92.00%

91.00%

90.00%

89.00%

88.00%

87.00%

86.00%

85.00%

84.00%

efficiency (

83.00%

82.00%

81.00%

80.00%

79.00%

78.00%

77.00%

76.00%

75.00%

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210

95.00%

94.00%

93.00%

92.00%

91.00%

90.00%

89.00%

88.00%

87.00%

86.00%

85.00%

84.00%

efficiency (

83.00%

82.00%

81.00%

80.00%

79.00%

78.00%

77.00%

76.00%

75.00% 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210

Outp u t po w e r (W)

Output power (W)

eff% @ 90 Vac eff% @ 100 Vac eff% @ 115 Vac eff% @ 135 Vac

eff% @ 170 Vac eff% @ 200 Vac eff% @ 230 Vac eff% @ 264 Vac

2.2 Resonant stage operating waveforms

Figure 7 shows some waveforms during steady state operation of the resonant circuit at full

load. The Ch3 waveform is the half-bridge square voltage on Pin 14 of L6599, driving the resonant circuit. In the picture it is not evident, but the switching frequency is normally slightly modulated following the PFC pre-regulator 100-Hz ripple that is rejected by the resonant control circuitry. The switching frequency has been selected approximately at 95-kHz in order to have a good trade off between transformer losses and dimensions.

The Ch4 waveform represents the transformer primary current flowing into the resonant tank. As shown, it is almost sinusoidal because the operating frequency is close to the resonance of the leakage inductance of the transformer and the resonant capacitor (C28). In this condition, the circuit has a good margin for ZVS operation, providing good efficiency,

11/35

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