ST AN2485 Application note

AN2485

Application note

400 W FOT-controlled PFC pre-regulator with the L6563

Introduction

This application note describes an evaluation board based on the Transition-mode PFC controller L6563 and presents the results of the bench evaluation. The board implements a 400 W, wide-range mains input, a PFC pre-conditioner suitable for ATX PSU, or a flat screen display. The chip is operated with Fixed-Off-Time control in order to use a low-cost device like the L6563 which is usually prohibitive at this power level. Fixed-Off-Time control allows Continuous Conduction Mode operation which is normally achieved with more expensive control chips and more complex control architectures.

L6563 400W FOT PFC Demo board (EVAL6563-400W)

March 2007

Rev 1

1/29

www.st.com

Contents	AN2485

Contents

1	Main characteristics and circuit description . . . . . . . . . . . . . . . . . . . .		. 4
2	Test results and significant waveforms . . . . . . . . . . . . . . . . . . . . . . . . .		7
	2.1	Harmonic content measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	7
	2.2	Inductor current in FOT and L6563 THD optimizer . . . . . . . . . . . . . . . . .	10
	2.3	Voltage feedforward . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	11
	2.4	Start-up and RUN pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	14
	2.5	Start-up at light load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	15
	2.6	Open loop protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	16
	2.7	Power management/housekeeping functions . . . . . . . . . . . . . . . . . . . . . .	17
3	Layout hints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		18
4	Audible noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		20
5	Thermal measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		20
6	Conducted emission pre-compliance test . . . . . . . . . . . . . . . . . . . . . .		22
7	Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		23
8	PFC coil specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		26
	8.1	General description and characteristics . . . . . . . . . . . . . . . . . . . . . . . . . .	26
	8.2	Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	26
	8.3	Mechanical aspect and pin numbering . . . . . . . . . . . . . . . . . . . . . . . . . . .	27
9	References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		28
10	Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		28

2/29

AN2485	List of figures

List of figures

Figure 1.	EVAL6563-400W evaluation board: electrical schematic . . . . . . . . . . . . . . . . . . . . . . . . . .		. 6
Figure 2.	EVAL6563-400W compliance to EN61000-3-2 at 230 Vac-full load . . . . . . . . . . . . . . . . .		. 7
Figure 3.	EVAL6563-400W compliance to JEIDA-MITI at 100 Vac-full load . . . . . . . . . . . . . . . . . . . .		7
Figure 4.	EVAL6563-400W compliance to EN61000-3-2 at 230 Vac-70 W load . . . . . . . . . . . . . . . .		7
Figure 5.	EVAL6563-400W compliance to JEIDA-MITI at 100 Vac-70 W load . . . . . . . . . . . . . . . . . .		7
Figure 6.	EVAL6563-400W Input current waveform at 100 V - 60 Hz - 400 W load . . . . . . . . . . . . . .		8
Figure 7.	EVAL6563-400W Input current waveform at 230 V - 50 Hz - 400 W load . . . . . . . . . . . . . .		8
Figure 8.	EVAL6563-400W Input current waveform at 100 V - 60 Hz - 200 W load . . . . . . . . . . . . . .		8
Figure 9.	EVAL6563-400W Input current waveform at 230 V - 50 Hz - 200 W load . . . . . . . . . . . . . .		8
Figure 10.	EVAL6563-400W Input current waveform at 100 V - 60 Hz - 70 W load . . . . . . . . . . . . . . .		8
Figure 11.	EVAL6563-400W Input current waveform at 230 V - 50 Hz - 70 W load . . . . . . . . . . . . . . .		8
Figure 12.	Power Factor vs. Vin and load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		9
Figure 13.	THD vs. Vin and load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		9
Figure 14.	Efficiency	vs. Vin and load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	9
Figure 15.	Static Vout	regulation vs. Vin and load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	9
Figure 16.	EVAL6563-400W Inductor current ripple envelope at 115 Vac - 60 Hz - full load . . . . . . .		10
Figure 17.	EVAL6563-400W Inductor current ripple (detail) at 115 Vac - 60 Hz - full load . . . . . . . . .		10
Figure 18.	EVAL6563-400W Inductor current ripple envelope at 230 Vac - 50 Hz - full load . . . . . . .		11
Figure 19.	EVAL6563-400W Inductor current ripple (detail) at 230 Vac - 50 Hz - full load . . . . . . . . .		11
Figure 20.	EVAL6563-400W Input mains surge from 90 Vac to 140 Vac - full load - CFF = 470 nF . .		12
Figure 21.	L6562 FOT Input mains surge from 90 Vac to 140 Vac - full load - NO VFF input . . . . . . .		12
Figure 22.	EVAL6563-400W Input mains dip from 140 Vac to 90 Vac - full load - CFF = 470 nF . . . .		13
Figure 23.	L6562 FOT Input mains dip from 90 Vac to 140 Vac - full load - NO VFF input . . . . . . . . .		13
Figure 24.	EVAL6563-400W Input current shape at 100 Vac-60 Hz vs. VFF ripple - CFF = 470 nF . . 14
Figure 25.	EVAL6563-400W Input current shape at 100 Vac-60 Hz vs. VFF ripple - CFF = 1.5 uF . . .		14
Figure 26.	EVAL6563-400W start-up at 90 Vac-60 Hz - full load . . . . . . . . . . . . . . . . . . . . . . . . . . . .		14
Figure 27.	EVAL6563-400W start-up at 265 Vac-50 Hz - full load . . . . . . . . . . . . . . . . . . . . . . . . . . .		14
Figure 28.	EVAL6563-400W start-up at 80 Vac-60 Hz - full load . . . . . . . . . . . . . . . . . . . . . . . . . . . .		15
Figure 29.	EVAL6563-400W Start-up at 265 V -50 Hz - 30 mA load. . . . . . . . . . . . . . . . . . . . . . . . . .		15
Figure 30.	EVAL6563-400W start-up at 265 V -50 Hz - no load . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		15
Figure 31.	EVAL6563-400W open loop at 115 Vac-60 Hz - full load. . . . . . . . . . . . . . . . . . . . . . . . . .		16
Figure 32.	L6563 On/Off control by a cascaded converter controller via PFC_OK or RUN pin . . . . .		17
Figure 33.	Interface circuits that let the L6563/A switch on or off a PWM controller . . . . . . . . . . . . . .		18
Figure 34.	EVAL6563-400W PCB layout (not 1:1 scaled) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		19
Figure 35.	Thermal map at 115 Vac-60 Hz - full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		21
Figure 36.	Thermal map at 230 Vac-50 Hz - full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		21
Figure 37.	115 Vac and full load - phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		22
Figure 38.	115 Vac and full load - neutral . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		22
Figure 39.	230 Vac and full load - phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		22
Figure 40.	230 Vac and full load - neutral . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		22
Figure 41.	Electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		26
Figure 42.	Pin side view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		27
Figure 43.	Mechanic aspect. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		27

3/29

Main characteristics and circuit description	AN2485

1 Main characteristics and circuit description

The main characteristics of the SMPS are:

●Line voltage range: 90 to 265 Vac

●Minimum line frequency (fL): 47 Hz

●Regulated output voltage: 400 V

●Rated output power: 400 W

●Maximum 2fL output voltage ripple: 10 V pk-pk

●Hold-up time: 22 ms (VDROP after hold-up time: 300 V)

●Maximum switching frequency: 85 kHz (@Vin=90 Vac, Pout=400 W)

●Minimum estimated efficiency: 90% (@Vin=90 Vac, Pout=400 W)

●Maximum ambient temperature: 50 °C

●EMI: in acc. with EN55022 Class-B

●PCB type and size: Single side, 70 um, CEM-1, 148.5 x 132 mm

●Low profile design: 35 mm component maximum height

The evaluation board implements a Power Factor Correction (PFC) pre-regulator delivering 400 W continuous power on a regulated 400 V rail from a wide range mains voltage. The board provides for the reduction of the mains harmonics which allows meeting the standards of the European norm EN61000-3-2 or the Japanese norm JEIDA-MITI. This rail is the input for the cascaded isolated DC-DC converter that provides the output rails required by the load.

The board is equipped with enough heat sinking to allow full-load operation in still air. With an appropriate airflow, and without any change in the circuit, the evaluation board can easily deliver up to 450 W.

The controller is the L6563 (U1), integrating all the functions needed to control the PFC stage and to interface with the downstream converter. The L6563 controller chip is designed for Transition-Mode (TM) operation, where the boost inductor works next to the boundary between Continuous (CCM) and Discontinuous Conduction Mode (DCM). However, with a slightly different usage, the chip can operate so that the boost inductor works in CCM, surpassing the limitations of TM operation in terms of power handling capability. The gatedrive capability of the L6563 is also adequate to drive the MOSFETs used at higher power levels. This approach, which couples the simplicity and cost-effectiveness of TM operation with the high-current capability of CCM operation, is the Fixed-Off-Time (FOT) control. The control modulates the ON-time of the power switch, while its OFF-time is kept constant. More precisely, the Line-Modulated FOT (LM-FOT), where the OFF-time of the power switch is not rigorously constant but is modulated by the instantaneous mains voltage, will be used. Please refer to AN1792 (“Design of Fixed-Off-Time-Controlled PFC Pre-regulators with the L6562”) for a detailed description of this technique as indicated in Section 9: References (point 2).

The power stage of the PFC is a conventional boost converter, connected to the output of the rectifier bridge D2. It includes the coil L4, the diode D3 and the capacitors C6 and C7. The boost switch is represented by the power mosfets Q1 and Q2. The NTC R2 limits the inrush current at switch on. It has been connected on the DC rail, in series to the output electrolytic capacitor, in order to improve efficiency during low line operation. Additionally, the splitting in two of output capacitors (C6 and C7) provides for managing the AC current

4/29

AN2485	Main characteristics and circuit description

mainly by the film capacitor C7 which allows for a less costly electrolytic to bear only the DC part.

At start-up the L6563 is powered by the Vcc capacitor (C12) that is charged via the resistors R3 and R4. The L4 secondary winding (pins #8-11) and the charge pump circuit (R5, C10, D5 and D4) generate the Vcc voltage powering the L6563 during normal operations.

The divider R32, R33 and R34 provides the L6563 multiplier with the information of the instantaneous voltage that is used to modulate the boost current. The instantaneous voltage information is also used to get the average value of the AC line by the VFF (Voltage FeedForward) pin. Divider R9, R10, R11, R12, and R13 is dedicated to sense output voltage while divider R6, R7, R8, and R24 is dedicated to protect the circuit in case of voltage loop failures. The Line-Modulated FOT is obtained by the timing generator components D6, C15, R15, C16, R16, R31, and Q3.

The board is equipped with an input EMI filter designed for a 2-wire input mains plug. It is composed of two stages, a Common Mode Pi-filter connected at the input (C1, L1, C2, C3) and a Differential Mode Pi-filter after the input bridge (C4, L3, C5). The board also offers the possibility to easily connect a downstream converter and test the interface signals managed by the L6563.

5/29

6/29

Main

JP101

.1 Figure

characteristics

JUMPER

D1

L3

+400Vdc

1

2

D2

DM-51uH-6A

L4

1N5406

PQ40-500uH

D15XB60

F1

CM-1.5mH-5A

5-6

1-2

D3

R2

L2

~

+

J2

J1

L1

RES

1

8A/250V

STTH8R06

NTC 2R5-S237

1

+400Vdc

R1

C1

C2

C3

C4

C5

8

11

C6

2

+400Vdc

description circuit and

2

3

NC

1M5

470nF-X2

470nF-X2

680nF-X2

470nF-630V

470nF-630V

470nF-630V

C7

4

RTN

~

-

330uF-450V

5

RTN

evaluation 400W-EVAL6563

1

2

90 - 265Vac

C8

C9

+400Vout

RES

RES

JP102

JUMPER

R3

180K

R5

+400Vdc

47R

R9

R10

680k

680k

R4

C10

R102

180K

18N

R6

0R0

D4

2M2

LL4148

R11

R7

680k

D5

2M2

C11

C12

BZX85-C15

470nF/50V

47uF/50V

R8

R12

R13

C13

2M2

100nF

82K

15k

C14

R14

U1

board:

1uF

56k

L6563

1

14

INV

VCC

2

13

COMP

GD

LL4148

electrical

3

12

C15

D6

MULT

GND

100pF

4

11

CS

ZCD

D7

R36

LL4148

5

10

3R9

VFF

RUN

R28

RES

R15

6

9

3K3

R17

Q1

TBO

PWM-STOP

J3

R16

6R8

STP12NM50FP

R29

1

C16

15K

7

8

RES

220pF

schematic

2

PFC-OK

PWM-LATCH

R35

3

3R9

D8

R24

C17

RES

R31

LL4148

36K

10nF

1k5

R30

Q2

RES

STP12NM50FP

R18

6R8

R26

R19

C18

150k

R27

C19

1K0

470nF

240k

2nF2

C20

330pF

R20

R21

R22

R23

0R39-1W

0R39-1W

0R39-1W

0R39-1W

R32

R33

Q3

BC857C

620k

620k

R101

AN2485

R34

C21

0R0

10k

10nF

AN2485	Test results and significant waveforms

2 Test results and significant waveforms

2.1Harmonic content measurement

One of the main purposes of a PFC pre-conditioner is the correction of input current distortion, decreasing the harmonic contents below the limits of European and Janapese regulations. The board has been tested according to European norm EN61000-3-2 Class-D and Japanese norm JEIDA-MITI Class-D, at full load and 70 W output power, at both the nominal input voltage mains.

As shown in Figure 2, 3, 4, and 5, the circuit is able to reduce the harmonics well below the limits of both regulations from full load down to light load. 70 W of output power has been chosen because it is almost the lower power limit at which the harmonics must be limited according to these international norms.

Figure 2. EVAL6563-400W compliance to								Figure 3. EVAL6563-400W compliance to
			EN61000-3-2 at 230 Vac-full load								JEIDA-MITI at 100 Vac-full load
			Measured value				EN61000-3-2 Class-D limits				Measured value JEIDA-MITI Class-D limits
	10								10
[A]	1							[A]	1
Current	0.1							Current	0.1
Harmonic	0.01							Harmonic	0.01
0.001									0.001
									1	3	5	7	9	11 13 15 17 19 21 23 25 27 29 31 33 35 37 39
	1	3	5	7	9	11 13 15 17 19 21 23 25 27 29 31 33 35 37 39
						Harmonic Order [n]								Harmonic Order [n]
Figure 4. EVAL6563-400W compliance to								Figure 5. EVAL6563-400W compliance to
			EN61000-3-2 at 230 Vac-70 W load								JEIDA-MITI at 100 Vac-70 W load

Measured value EN61000-3-2 Class-D limits

	1						1
[A]						[A]
Current	0.1					Current	0.1
Harmonic	0.01					Harmonic	0.01
0.001							0.001
	1	3	5	7	9	11 13 15 17 19 21 23 25 27 29 31 33 35 37 39
						Harmonic Order [n]

Measured value JEIDA-MITI Class-D limits

1

3

5

7

9

11 13 15 17 19 21 23 25 27 29 31 33 35 37 39

Harmonic Order [n]

For user reference, waveforms of the input current and voltage at the nominal input voltage mains and different load conditions are given in Figure 6, 7, 8, 9, 10, and 11.

7/29

Test results and significant waveforms	AN2485
Figure 6. EVAL6563-400W Input current	Figure 7. EVAL6563-400W Input current
waveform at 100 V - 60 Hz - 400 W	waveform at 230 V - 50 Hz - 400 W
load	load

Figure 8. EVAL6563-400W Input current	Figure 9. EVAL6563-400W Input current
waveform at 100 V - 60 Hz - 200 W	waveform at 230 V - 50 Hz - 200 W
load	load

Figure 10. EVAL6563-400W	Input current	Figure 11. EVAL6563-400W Input current
waveform at 100	V - 60 Hz - 70 W	waveform at 230 V - 50 Hz - 70 W
load		load

8/29

AN2485	Test results and significant waveforms

The Power Factor (PF) and the Total Harmonic Distortion (THD) have been measured too and the results are reported in Figure 12. and Figure 13. As shown, the PF at full load and half load remains close to unity throughout the input voltage mains range while it decreases at high mains range when the circuit is delivering 70 W. THD is low, remaining within 25% at maximum input voltage.

Figure 12. Power Factor vs. Vin and load							Figure 13. THD vs. Vin and load
PF							THD [%]
1.05							30
1							25				400W
0.95											200W
							20				70W
0.9
				400W			15
0.85				200W
0.8				70W			10
0.75							5
0.7							0
90	100	115	130	180	230	265	90	100	115	130	180	230	265
			VIN [VRMS]							VIN [VRMS]

Efficiency is very good at all load and line conditions. At full load it is always significantly higher than 90%, making this design suitable for high efficiency power supply.

The measured output voltage variation at different line and load conditions is given in Figure 15. As shown, the voltage is perfectly stable over the input voltage range due to the Voltage Feed-Forward function embedded in the L6593. Only at 265 Vac and light load, there is a negligible deviation of 1 V due to the intervention of the burst mode (for the "static OVP") function.

Figure 14. Efficiency vs. Vin and load	Figure 15. Static Vout regulation vs. Vin and
	load

Eff [%]							VOUT [VDC]
100%							404
							403.5	400W
95%								200W
							403	70W
90%							402.5	15W
							402
85%				400W			401.5
				200W
				70W			401
80%
				15W			400.5
75%							400
90	100	115	130	180	230	265	90	100	115	130	180	230	265
			VIN [VRMS]							VIN [VRMS]

9/29