ST AN2264 APPLICATION NOTE

AN2264

APPLICATION NOTE

Three-Phase SMPS for low power applications with VIPer12A

Introduction

Some industrial applications require a so called 'ultra-wide' input voltage range (between 90 and 450Vac). Due to the variations of the main, input voltages up to 450Vac are typical in threephase applications. A maximum input voltage of 450Vac requires the use of very high voltage components, increasing cost, size, the weight and the overall complexity of the power supply. Hence, the market is looking for solutions with low cost and good performance.

Thi document introduces a cost effective solution for low power high voltage power supplies. The proposed solution consists of in an off-line SMPS and a low cost front-end regulation circuit for input voltage limiting. Such a circuit allows proper operation of the power converter avoiding the use of voltage over-rated components, both passive and active. The circuit is suitable for any off-line SMPS topology since it includes a switching transistor connected between the input rectifier and the DC bulk capacitor (STMicroelectronics patent pending). The series switch limits the DC input voltage of the power converter by means of a suitable driving circuit; thus the SMPS primary transistor can be selected as a standard part as well as a smart power primary IC.

Typical end applications of this solution can be found in the industrial market in the range below 5W, such as three-phase and single phase power meter, industrial bias power supply and auxiliary SMPS for high voltage street-lighting, where the input voltage can range between 90Vac and 450Vac and 1000V power MOSFETs are currently used.

As an example of industrial applications, a flyback converter for supplying an electronic power meter is considered. The use of the proposed approach in a power converter designed for 265Vac maximum input voltage allows the operating input voltage to be extended up to 450Vac or higher with no damages to the converter components. Thus, the major benefit of such solution is a significant cost saving thanks to the reduction of components voltage rating.

Figure 1. Board Prototype

	Rev 1.0
AN2264/1105	1/42

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AN2264

Contents

1 Application Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2 Circuit Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.1	Input Voltage Limiting Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	13
3.2	Steady State Behaviour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	14
3.3	Line And Load Regulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	28
3.4	Hold-up Time Capability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	29
3.5	Additional Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	30
3.6	Measurements At The Start-Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	31

4 Conducted Emissions Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

5 Thermal Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

7 Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

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AN2264

Figures

Figure 1. Board Prototype . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Figure 2. Circuit Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Figure 3. PCB Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Figure 4. Flyback Transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Figure 5. MOSFET STD3NK50Z Operation at FULL LOAD and Vin = 450 Vrms . . 13 Figure 6. VIPer12AS Vds & Id at FULL LOAD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Figure 7. VIPer12AS Vds & Id at HALF LOAD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Figure 8. VIPer12AS Vds & Id at MINIMUM LOAD . . . . . . . . . . . . . . . . . . . . . . . . . 22 Figure 9. STD3NK50Z Vds & Id at FULL LOAD. . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Figure 10. Line Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Figure 11. Load Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Figure 12. Hold-up Time Capability at FULL LOAD . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Figure 13. Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Figure 14. VIPer12AS and Outputs-Start-up at FULL LOAD . . . . . . . . . . . . . . . . . . . 31 Figure 15. STD3NK50Z-1 Start-up at FULL LOAD . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Figure 16. Start-up at MINIMUM LOAD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Figure 17. Conducted Emissions - at Vin=230Vac - FULL LOAD . . . . . . . . . . . . . . . 34 Figure 18. Conducted Emissions - at Vin=380Vac - FULL LOAD . . . . . . . . . . . . . . . 35 Figure 19. Thermal Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

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AN2264

Tables

Table 1. Operating conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Table 2. Three-Phase Electricity Meter Voltage Marking . . . . . . . . . . . . . . . . . . . . . 5 Table 3. Bill of Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Table 4. Full Load (Iout ≈100mA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Table 5. Half Load (Iout≈50mA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Table 6. Minimum Load (Iout=10mA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

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AN2264	1 Application Description

1 Application Description

The present SMPS has been designed according to the following specifications:

Table 1.	Operating conditions
	Parameter	Value
Input Voltage Range		90 to 450 Vac
Input Frequency Range		50/60 Hz
Output Voltage 1		V1=5V
Output Voltage 2		V2=3.3V
Output Current 1		I1=10mA
Output Current 2		I2=100mA
Output Power (peak)		550mW
Line Regulation		+/- 1%
Load Regulation		+/- 1%
Output Ripple Voltage 1		50mV
Hold-up capability		> 40 ms (*)
Safety		EN60950
EMI		EN55022 class B

(*) Considering the STPM01 roll over time (31ms) and the Memory M95040 write time per data (5ms).

In addition to the previous specs, the power supply has to be compliant also with the standards of electricity meters, i.e. IEC 62052-11 and IEC 62053-21, since it has been specifically developed for such an application. The main prescriptions are listed here below:

● Input connection and voltage marking (EN62052-11):

Table 2.	Three-Phase Electricity Meter Voltage Marking
	Meter		Rated System Voltage (V)
Single-phase 2 wire 120V			120
Single-phase 3 wire 120V (120V to the mid-wire)			240
Three-Phase 3 wire 2-element (230		V between phases)	400
Three-Phase 4 wire 3-element (230		V phase to neutral)	400

●Pulse Voltage Test (EN62052-11):

-Pulse waveform: according IEC 60060-1

-Voltage rise time: ±30%

-Voltage fall time: ±20%

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1 Application Description	AN2264

-Source impedance: 500Ω ± 50Ω

-Source Energy: 0.5J ±0.05J

-Rated Pulse Voltage: 4000V

-Test Voltage Tolerance: +0 -10%

●Mean input power : 2W according to EN62053-21 (Switching power supplies with peak power values exceeding the specified value are also permitted)

●Temperature Range: -25°C ± 3°C ÷ +70°C ± 2°C (EN 62052-11)

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AN2264	2 Circuit Description

2 Circuit Description

The schematic of the board is shown in Figure 2.

A 3-phase 4-wire bridge is used for mains rectification because the neutral rectification is needed to ensure proper operation in case of missing neutral connection or neutral mis-wiring.

A varistor is connected between each line and neutral to guarantee pulse voltage test immunity according to the EN62052-11 standard.

The input EMI filter is a simple undamped LC-filter for both differential and common mode noise suppression.

The circuit for input voltage limiting is connected between the input EMI filter and the bulk capacitor C4. Such a circuitry includes a Power MOSFET and a self driven control section. The MOSFET Q1 is a standard N-Channel 500V 3.3Ω in D-PAK package, mounted on a small copper area to improve thermal performance. The self driven control section consists of a voltage divider and zener diodes. The resistors R1, R2 and R3 ensure the gate-source charge for the switch, while the zener diodes D3 and D4 set the maximum voltage value (360V) across the bulk capacitor.

An NTC limits the inrush current and ensures Q1 operation inside its safe operating area.

The flyback converter is based on VIPer12AS, a member of the VIPerX2A family, which combines a dedicated current mode off-line PWM controller with a high voltage power MOSFET on the same silicon chip. The switching frequency is fixed at 60kHz by the IC internal oscillator allowing, to optimize the transformer size and cost. The transformer reflected voltage has been set to 60V, providing enough margin for the leakage inductance voltage spike and no snubber circuit is needed with a consequent cost saving.

As soon as the voltage is applied on the input of the converter the high voltage start-up current source connected to the drain pin is activated and starts to charge the Vdd capacitor C8 through a constant current of 1mA. When the voltage across this capacitor reaches the Vddon threshold (about 14V) the VIPer12AS starts to switch. During normal operation the smart power IC is powered by the auxiliary winding of the transformer via the diode D7. No spike killer for the auxiliary voltage fluctuations is needed thanks to the wide range of the Vdd pin (9-38V). The primary current is measured using the integrated current sensing for current mode operation.

The output rectifier D6 has been chosen in accordance with the maximum reverse voltage and power dissipation; in particular a 0.5A-80V Schottky diode, type TMBAT49, has been selected.

The output voltage regulation is performed by secondary feedback on the 5V output dedicated to the display, while the 3.3V output, dedicated to the logic part and the microcontroller, is linearly post-regulated from the 5V output. This operation is performed by a very low drop voltage regulator, L4931ABD33, in SO-8 package. The voltage regulator delivers up to 100mA, ensuring good reliability with no heat sink. The feedback network ensures the required insulation between the primary and secondary sections. The optotransistor directly drives the VIPer12AS feedback pin which controls the IC operation.

A small LC filter has been added to the 5V output in order reduce the high frequency ripple with reasonable output capacitors value.

The flyback transformer is a layer type based on E13 core and N27 ferrite, manufactured by Pulse Eldor, and ensures safety insulation in accordance with the EN60950. Figure 4. shows the main features of the transformer.

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8/42

RF1

L1

NTC1

Q1

C1

P1

22E 0.75W

1mH

50E

STD3NK50Z

2.2nF/2kV (Y1)

RV1

2

3

2

D1

D6

L2

SO5K275/275V

5V@10mA

VDD

R1

1

T1

TMBAT49

10uH 100mA SMD

D5

RV2

4

-

+

3

C2

330K SMD

1

10

ZMM 15

SO5K275/275V

220nF

R2

SOD-80

C5

+

C6

+

630V

C4

2

6

330uF 25V

22uF 25V

RF2

SMD

330K SMD

P2

1

BRIDGE

2.2uF450V

22E 0.75W

3.3V

+

P3

C3

R3

RF3

2

330K SMD

220nF

22E 0.75W

D2

4

U2

L4931ABD33

630V

3.3V@100mA

RV3

4

-

+

3

SMD

D3

R4

8

VIN

VOUT

1

SO5K275/275V

180V

5

GND

GND GND GND

SMD

NC INH

10E

C7

+

RF4

D4

2.2uF 25V

N

22E 0.75W

1

BRIDGE

180V

D7

2 3 6 7

4 5

R7

LL4148

R5

R6

4.7K

220E SMD

1K

SMD

SMD

U4

R9

PC817

GND

C8

4

1

5.6K SMD

10uF 50V

+

U1

3

2

4

5 6 7 8

C9

Vdd

D D D D

1U3

100nF

Note:

3

50V

FB

TS2431

SMD

VIPer12AS

3

Layout Hints: Q1 mounted on 1cm x 0.8cm copper

S S

area. C8&C10 have to be closed to the VIPer12AS.

2

R8

2 1

GND Pins for U2 have to be soldered to a unique

4.7K SMD

copper area.

C10

47nF

50V

SMD

.2 Figure	whole The .mm 38 x	Description Circuit2
Schematic Circuit	been has supply power
	78 measuring 4,-FR in PCB 35um side double a on realized	AN2264

AN2264	2 Circuit Description

Figure 3. PCB Layout

Top side-silk screen (in scale)

Bottom sidesilk screen (in scale)

Top side-copper tracks (in scale)

Bottom side-copper tracks (in scale)

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2 Circuit Description	AN2264

Figure 4. Flyback Transformer

2.2mH ±20% < 2% 11 3

):
p
Primary Inductance: Primary Leakage Inductance (%L	Primary to secondary turn ratio: Auxiliary to secondary turn ratio:

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AN2264			2 Circuit Description
	Table 3. Bill of Materials
	Reference	Value	Description
	CON1, CON2		Hartmann/ptr, 2 poles, type PK 7402, 380VAC 16A
	CON3		Hartmann/ptr, 3 poles, type PK 3503, 380VAC 16A
	C1	2.2nF/2kV	Cera-Mite Corporation 44LD22 Y1 Ceramic Capacitor 20%
	C2, C3	220nF 630V	TDK C5750X7R2J224M SMD Ceramic Capacitor 20%
	C4	2.2uF450V	Rubycon Aluminium Radial Lead Electrolytic Capacitor YK
			Series 29mA 20%
	C5	330uF 25V	Rubycon Aluminium Radial Lead Electrolytic Capacitor ZL
			Series 56mR 995mA 20%
	C6	22uF 16V	Rubycon Aluminium Radial Lead Electrolytic Capacitor ZA
			Series 270mR 350mA 20%
	C7	2.2uF 50V	Panasonic ECA1HHG2R2 NHG-A Radial Lead Electrolytic
			Capacitor 18mA 20%
	C8	10uF 50V	Panasonic ECA1HHG100 NHG-A Radial Lead Electrolytic
			Capacitor 39mA 20%
	C9	100nF 50V	muRata GRM40X7R104Z50 SMD Ceramic Capacitor 20%
	C10	47nF 50V	muRata GRM40X7R473Z50 SMD Ceramic Capacitor 20%
	D1, D2	BRIDGE	General Instruments DF10S SMT Diode Bridge 1000V 1A
	D3, D4	ZY180V	DO-41 Zener Diode 180V 2W 5%
	D5	ZMM 15/SOD-80	Mini-Melf Zener Diode 15V 0.5W 5%
	D6	TMBAT49	STMicroelectronics Small Signal Schottky Diode 80V 0.5A
	D7	LL4148/SOD-80	SOD-80 General Purpose Rectifier 75V 200mA
	L1	1mH	Epcos B78108-S1105J , Bobbin Core BC 130mA 13R 10%
	L2	10uH	TDK GLF2012T100M SMD Signal-Use SMD Inductor 125mA
			20%
	NTC1	50E	UEI 10SP050L Inrush Current Suppressor 50R 2A 10%
	Q1	STD3NK50Z	STMicroelectronics N-Channel Mosfet 500V 2.3A 3.3R
	RF1, RF2, RF3,	22E 0.75W	Yageo Resistor, wire wound, fusible, 22R 0.75W 5%
	RF4
	RV1, RV2, RV3	SO5K275/275V	Epcos B72650M271K72 SMD Varistor 275VAC 8.6J
	R1, R2, R3	330K SMD	Resistor, Metal Film 0.25W 5%
	R4	10E SMD	Resistor, Metal Film 0.25W 5%
	R5	220E SMD	Resistor, Metal Film 0.25W 5%
	R6	1K SMD	Resistor, Metal Film 0.25W 5%
	R7	4.7K SMD	Resistor, Metal Film 0.25W 5%
	R8	4.7K SMD	Resistor, Metal Film 0.25W 5%
	R9	5.6K SMD	Resistor, Metal Film 0.25W 5%

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2 Circuit Description			AN2264
	Table3. Bill of Materials (Continued)
	Reference	Value	Description
	T1	2432.0015C	E13 TIW Pulse Eldor Switch Mode Transformer
	U1	VIPer12AS	STMicroelectronics Off Line SMPS Primary IC 730V 0.4A
			27R
	U2	L4931ABD33	STMicroelectronics Very Low Drop Voltage Regulator
			3.3V 300mA 1%
	U3	TS2431	STMicroelectronics Programmable Shunt Voltage
			Reference 1%
	U4	PC817	Sharp Optocoupler 5kV

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AN2264	3 Experimental Results

3 Experimental Results

3.1Input Voltage Limiting Circuit

The main waveforms of the input voltage limiting circuit are shown in Figure 5. In particular the waveforms refer to the start-up and the steady-state operations at 450Vac and full load ,which are the worst conditions for the device. The advantages of this solution are evident. It limits the DC voltage at the given reference value, in this case 360V, and avoides the use of over-rated components compared to the standard off-line power supply.

Figure 5. MOSFET STD3NK50Z Operation at FULL LOAD and Vin = 450 Vrms

Start-Up

CH1: INPUT VOLTAGE (Blue)

CH2: DRAIN CURRENT (Red)

CH3: DRAIN-SOURCE VOLTAGE (Green)

Steady State

CH1: DRAIN VOLTAGE (Blue)

CH2: DRAIN CURRENT (Red)

CH3: SOURCE VOLTAGE (Green)

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