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 Vac).

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

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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 Vac - full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Figure 17. Thermal map at 230 Vac - full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Figure 18. CE quasi peak measurement at 115 Vac and full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Figure 19. CE quasi peak measurement at 230 Vac and full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 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

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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 Vac and frequencies between 45 and 65 Hz

●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 Vac

●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.
	The PFC stage delivers a stable 400 VDC 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 VFF (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,

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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 (VAUX) necessary to start-up the 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.

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6/35

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7/35

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AN2393

AN2393	Electrical test results

2 Electrical test results

2.1Efficiency measurements

Table 1 and Table 2 show the output voltage measurements at the nominal mains voltages of 115 Vac and 230 Vac, with different load conditions. For all measurements, both at full load 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 @VIN = 115 Vac
+24 V(V) @load(A)		+12 V(V) @load(A)	+5 V(V) @load(A)	+3.3 V(V) @load(A)	POUT (W)	PIN (W)	Efficiency

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%

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 @VIN = 230 Vac
+24 V(V) @load(A)		+12 V(V) @load(A)	+5 V(V) @load(A)	+3.3 V(V) @load(A)	POUT (W)	PIN (W)	Efficiency

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%

In Table 1, Table 2 and Figure 5 the overall circuit efficiency is measured at each load condition, at both nominal input mains voltages of 115 Vac 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 VIN = 90 Vac - full load, the efficiency is 86.88% (POUT = 208.8 W and PIN = 240.3 W)

●At VIN = 264 Vac - full load, the efficiency is 90.90% (POUT = 208.7 W and PIN = 229.6 W)

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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%
efficiency	86.00%																					eff% @ 115 Vac
	85.00%																					eff% @ 115 Vac
	85.00%																					eff% @ 230 Vac
	84.00%																					eff% @ 230 Vac
	84.00%
	83.00%
	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
										Output power (W)

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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%
efficiency	86.00%
	85.00%
	84.00%
	83.00%
	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

Output power (W)

	95.00%
	94.00%
	93.00%
	92.00%
	91.00%
	90.00%
	89.00%
	88.00%
(%	87.00%
(%	86.00%
efficiency	86.00%
	85.00%
	84.00%
	83.00%
	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

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

2.2Resonant 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,

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