ST AN1897 Application note

AN1897

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®

- APPLICATION NOTE

VIPower: LOW COST UNIVERSAL INPUT

DVD SUPPLY WITH VIPer22A

Jun-fen g Zhang

INTRODU CTI ON

In the past few years, many consumer products have been provid ed to the end user, such as DVD or VCD players. Generally their power supply require multiple outputs to supply a variety of control circuits: MCU, Motor, Amplifier, VFD.

ST VIPer series of off-line switch mode power supply regulators c ombines an optimized, high voltage, avalanche rugged Vertical Power MOSFET with current mode c ontrol PWM circuitry. The result is truly innovative AC to DC conversion that is simpler, quicker and - with component count halved - less expensive.

The VIPer family al so represents th e ea sies t s olution to com ply with the "Blue Angel" and "Energy Star" Eco norms, with extremely low total power consumption at stand-by mode, thanks to the burst operation.

This document would present the ap plication on DVD player pow er supply with VI Per22A satisfying the specification See table 1 below.

Table 1: Output Specification

INPUT OUTPUT 1 OUTPUT 2 OUTPUT 3 OUTPUT 4 OUTPUT 5 OUTPUT 6

Universal

mains lin e

Min: 85Vac

Max:

265Vac

Note 1: The accuracy of + /- 5% is reached only for a cer tain range of loads combination. See paragraph 3. 2 for cross regulation results.

5 V +/- 5%

(See note 1)

Imin: 20mA Imax: 1.5 A

+12 V +/- 5%

(See note 1)

Imax: 30 mA Imax: 30 mA Imax: 50mA Imax: 150mA Imax: 100mA

-12 V +/- 5% (See note 1)

-26 V + /- 5% (See note 1)

3.3 V +/- 5% (See note 1)

+/- 5%

5V

stb

(See note 1)

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AN1897 - APPLICATION NOTE

1. APPLICATION DESCRIPTION AND DESIGN

1.1 Schematics

The overall schematic is shown in figure 2.

1.1.1 Start-up Phase

As any member of the VIPer family, VIPer22A has an integrated high voltage current source linked to Drain pin . At the startup converter, it will charge the V

(14.5V), and then the VIPer22A starts switching.

1.1.2 Auxiliary Supply

VIPer22A has a wide operating voltage range from 8V to 42V, respectively minimum and maximum values for under-voltage and over-voltage protections.

This function is very useful for achievin g low stand-by total power consum ption. During norma l working, the feedback loop is connected to 5V output by D12 to regulate 5V output. At the mean time, +5Vstb output is blocked by Q3, so +5Vstb regulation is neglected. When the stand-by signal is present, the Vce of Q3 can not provide enough voltage to maintain D12 conducted, so the 5V output is blocked, and the +5Vstb output is connected to the feedback loop. In this condition the +5 Vstb is regulated. Thanks to the transformer structure, all the other secondary outputs and the auxiliary voltages are pulled down to a very low level, also pulling down the total power consumption.

All these contents can be summarized by the following list:

• in normal full load, the V

• in short circuit, the V

to the well known hiccup mode in practice;

• in no load condition, the V

voltage of the device must be lower than the over-voltage protection;

DD

voltage must be lower than the shutdown vol tage. Actually, this condition leads

DD

voltage must be higher than the shutdown voltage.

DD

capacitor until it reaches VIPer startup level

DD

1.1.3 Burst Mode

The Viper22A integrates a current mode PWM with a Power MOSFET and includes the leading edge blanking function. The burst mode is a feature which allows VIPer22A to skip some switching cycles

when the energy drained by the output load goes be low E =(T input voltage, f

It has the consequence to redu ce the switching losses when working in low load cond ition by reducing the switching frequency.

1.1.4 Feedback Loop

The 5V output voltage is regulated with a TL-431 (U3) via an optocoupler (U2) to the feedback pin. If the output voltage is high, the TL-431 will draw more current through its cat hode to t he anode and the current increases in the optocoupler diode. The current in optocoupler NPN increases accordingly and the current into the VIPer22A FB pin increases. When the FB current increases, the VIPer22A will skip some cycles to decrease turn on time and lower the output voltage to the proper level (see figure 1).

The 5V output voltage is regulated thanks to the reference voltage of TL-431 and the resistive divider R8 and R9.

2/11

=Switching frequency, Lp=Primary Inductance).

sw

)2 * fsw/2Lp (Tb=blanking time, Vin=DC

b*Vin

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Figure 1: VIPer22A FB pin internal structure

60kHz

OSCILLATOR

AN1897 - APPLICATION NOTE

DRAIN

Id

Secondary feedback

+Vdd

I

FB

C

0.23V

1 kΩ

S

PWM

Q

LATCH

R

Is

R1

230 Ω

R2

SOURCE

1.1.5 Primary Driver

In a fly-back power supply, the transformer is used as an energy tank fuelled during the ON time of the MOSFET. When the MOSFET turns off, its drain voltage rises from a low value to the input voltage plus the reflected voltage while the secondary diode conducts, transferring on the secondary side the magnetic energy stored in the transformer. Because primary and secondary windin gs are not perfectly magnetically coupled, there is a serial leakage inductance that behaves like an open inductor charged at

that causes the voltage spikes on the MOSFET drain. These voltage spikes must be clamped to keep

I

pk

the VIPer22A Drain voltage below the BVds s (730Vmin) rating. If the peak voltage is higher than this value, the device will be destroyed. The most used solution is the RCD clamp (see figure 3). This is a very simple and chea p solution, but it impacts on the efficiency and even on the power dissipation in stand-by condition. Also the clamping voltage varies with load current. RCD clamp circuits may allow the drain voltage to exceed the data sheet breakdown rating of VIPer22A during overload operation or during turn on with high line AC input voltage. So, a zener clamp is recommended (see figure 4). However such a solution gives higher power dissipation at full load, even if the clamp voltage is exactly defined.

1.2 Transformer Consideration

On the electrical specification of a multiple output transformer (cross regulation, leakage inductance), the main efforts focused on the proper coupling between the windings. A lower leakage inductance transformer will allow a lower power clamp to reduce the input power. It will lead to lower power dissipation on the primary side.

Auxiliary and secondary windings are swapped in order to decrease the coupling to the primary one. The secondary windings act as a shielding layer to reduce the capacitive coupling. Fewer spikes are generated on the auxiliary windings, the primary and secondary windings have better coupling.

Designing transformers for low leakage inductance involves several considerations:

•Minimize number of turns

•Keep winding build (ratio of winding height to width) small

•Increase width of windings

•Minimize insulation between windings

•Increase coupling between windings

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AN1897 - APPLICATION NOTE

Figure 2: Application schematic

J4

CON4

--12V / 0.03A

470uF/25V

C19

D13

BYW 100/ 2 00

CON5

F- (3.3Vac) / 0.15A

J3

12345

C25

100uF/10V

D11

1N5818

F+ (3.3Vac)

+12V / 0.03A

C17

D9

BYW 100/ 200

470uF/25V

123

4

--26V / 0.05A

C20

220uF/50V

C20

220uF/50V

C20

220uF/50V

D10

BYW 100/ 200

+5V / 1.5A

D8

STPS5L60

3.3V

GND

Vout

3

Vin

1

C15

100uF/10V

2

U4

LD33V

U4

LD33V

U4

LD33V

C13

470uF16V

C12

1000uF/16V

D12

D12 1N5818

1N5818

J5

123456789

1234567

123456789

CON9

+5Vstb / 0.1A

R11

680 ohm

C9

220uF/50V

D7

BYW 100/ 200

Q3

8550

8

9

STB

R9

R8

R9

R8

R9

R8

5.1K

R6

1K

C10

47pF

U1A

U3

817

R5

1K

U3

TL431

R4

1K

Q1

9014

151411131298

1

2

1

2

1

2

C5

47pF/1KV

D5

FR157

R3

C4

100k/1W

47uF/400V

1N4007D21N4007D11N4007

1N4007

D4

D3

D4

D3

D4

D3

RT1

NTC5D-9

2200pF Y1C12200pF Y1

C2

34

CH1

2.2mH

1 2

C3

0.1uF X2

2

1

CON2

0.1uF X2

1

2

1

2

1

2

CON2

J2

F1

250V 1A

F1

250V 1A

J1

10

7

10

7

D6

1N4937

R3

9.1K

DRAIN

VDD

U1B

817

TX1

TFO EC28---VER3

C7

47uF/50V

U2

SOURCE

CONTROL

VIPER22A

C6

47nF

2JP1

1

JUMPER

C8

1nF / 1KV

Auxilia ry Volt 10 Vmin

+ 5V 1.5A

Auxilia ry Volt 10 Vmin

+ 5Vstb 0.1A

- 12V 0.03A

+ 12V 0.03A

- 26V 0.05A

3.3Vac 0.15A

+ 5Vstb 0.1A

- 12V 0.03A

+ 12V 0.03A

- 26V 0.05A

3.3Vac 0.15A

+ 5Vstb 0.1A

- 12V 0.03A

+ 12V 0.03A

- 26V 0.05A

3.3Vac 0.15A

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AN1897 - APPLICATION NOTE

Figure 3: RCD clamp topology Figure 4: Zener clamp topology

For a transformer m eeting international insul ation a nd s afet y requi reme nts, a practical value for leak age inductance is about 1-3% of the open circuit primary inductance.

A high efficiency transformer should have low inter-winding capacitance to decrease the switching losses. Energy stored in the parasitic capacitance of the transformer is absorbed by VIPer cycle by cycle during the turn-on transition. Excess capacitance will also ring with stray inductance during switch transitions, causing noise prob lems. Capacitance effects are usually the m ost important in the primary winding, where the operating voltage (and consequent energy storage) is high. The primary winding should be the first winding on the transformer. This allows the primary winding to have a low mean length per turn, reducing the internal capacitance. The d riven end of the primary winding (the e nd c onne cted to the Drain pin) should be the beginning of the winding rather than the end.

This takes advantage of the shielding effect of the second half of the primary winding and reduces capacitive coupling to adjacent windings. A layer of insulation between adjacent primary windings can cut the internal capacitance of the primary winding by as much as a factor of four, with consequent reduction of losses. A common technique for winding multiple secondaries with the same polarity sharing a common return, is to stack the secondaries (see figure 5). This arrangement will improve the load regulation, and reduce the total number of secondary turns.

Commonly a clamper based on an RCD network or a diode with a zene r to clamp the rise of the dr ain voltage is used.

Figure 5: Multiple output winding

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AN1897 - APPLICATION NOTE

+12V/30mA, -12V/30mA, -26V/50mA,

2. LAYOUT RECOMMENDATION

Since EMI issues are strongly related to layout, a basic rule has to be taken into account in high current path routing, i.e. the current loop area has to be minimized. If a heat-sink is used it has to be connected to ground too, in order to reduce common mode emissions, since it is close to the floating drain tab.

One more consideration has to be made regarding the control ground connection: in fact in order to avoid any noise interference on VIPer logic pin the control ground has to be separated from power ground.

3. EXPERIMENTAL RESULT

3.1 Efficiency

Figure 6: Efficiency at 230Vac (Load on 5V) Figure 7: Efficiency at 260Vac (Load on 5V)

80.00%

70.00%

60.00%

50.00%

40.00%

30.00%

Efficiency

20.00%

10.00%

0.00%

+12V/30mA, -12V/30mA, -26V/50mA,

3.3V/0.15A

0.1A 0.5A 1A 1.5A 2A

Efficiency at 230Vac Mains Input

80.00%

70.00%

60.00%

50.00%

40.00%

30.00%

Efficiency

20.00%

10.00%

0.00%

0.1A 0.5A 1A 1.5A 2A

Efficiency at 260Vac Input

3.3V/0.15A

Figure 8: Efficiency at 85Vac (Load on 5V) Figure 9: Load Regulation (load on +5V)

Voltage

5.20

5.15

5.10

5.05

5.00

4.95

4.90

4.85

4.80 0A 0.1A 0.5A 1A 1.5A 2A

Load (A)

+5V Load Regualtion

76.00%

74.00%

72.00%

70.00%

68.00%

66.00%

Efficiency

64.00%

62.00%

60.00%

+12V/30mA, -12V/30mA, -26V/50mA,

3.3V/0.15A

0.1A 0.5A 1.0A 1.5A 2.0A

Efficiency at 85Vac Input

3.2 Re gulati on Table 2: Line regulation

Output 85Vac 230Vac 260Vac

5V/ 0.1A 5.15V 5.15V 5.15V 5Vstb/ 0A 5.15V 5.15V 5.15V 12V/ 0A 12.08V 12.11V 12.12V

-12V/ 0A -11.98V -11.99V -12.00V

-26V/ 0A -25.82V -25.85V -25.86V

3.3V/ 0A 3.87V 3.87V 3.88V

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Figure 10: Cross regulation

15.00

10.00

5.00

0.00

-5.00

-10.00

Voltage

-15.00

-20.00

-25.00

-30.00

AN1897 - APPLICATION NOTE

+5V/0.5A

0m A 10mA 30mA 50mA 100m A 150mA

Load (mA)

+12V -12V -26V 3.3V

Table 3: Stand by model

Output 85Vac 230Vac 260Vac

5V 5Vstb (100mA) 12V

-12V

-26V

3.3V Pdis

2.05V 2.05V 2.07V

5.08V 5.11V 5.14V

4.00V 3.99V 3.98V

3.99V 3.99V 3.98V

9.12V 9.10V 9.08V

1.70V 1.50V 1.51V

0.8W 1W 1.1W

Table 4: Full Load Regulation

Output 85Vac 230Vac 260Vac

5V/ 1.5A 5Vstb/ 0A 12V/30mA

-12V/30mA

-26V/50mA

3.3V/0.15A VIPer Temp

5.02V 5.09V 5.08V

12.03V 12.06V 12.05V

-12.01V -12.05V -12.05V

-26.06V -26.16V -26.15V

3.77V 3.80V 3.78V

53°C 47°C 45°C

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AN1897 - APPLICATION NOTE

4. TRANSFORMER SPECIFICATION

Figure 11: Transformer Structure

Primary inductance: Lp = 2.8 mH 1KHz, 0.3V Leakage inductance: Lk < 28uH at Seconda ry

and auxiliary winding short (1KHz, 0.3V)

Core: EER28L Bobbin: ER28 (6 + 9 Pin) Vendor: YuanDongDa electronics Co., Ltd

Table 5: Winding Parameters

Layers description Symbol Start Pin End Pin Number of Layer Turns Wire Size

(mm)

Primary Out1 (5V/1.5A) Out2 (12V/0.03A) Out3 (-12V/0.03A) Out4 (-26V/0.05A) Out5 (5Vstb/0.1A) Out6 (3.3V/0.15A) Auxiliary

B

O

B B

I

N

Wp

2 1

Wp Pin2 Pin1 2 65 0.3 W5 Pin7 Pin12 1 4 2*0.6

W12 Pin11 Pin7 1 5 0.3 W-12 Pin12 Pin10 1 9 0.45 W-26 Pin10 Pin13 1 10 0.3

Wstb Pin9 Pin8 1 12 0.3 W3v3 Pin14 Pin15 1 3 0.3 Waux Pin6 Pin5 1 24 0.3

Barrier (3mm)

12

W5

7

W12

11

10

W-12

12

Barrier (3mm)

13

W-26

10

15

W3v3

14

8

Wstb

9

5

Waux

6

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5. PCB LAYOUT

Figure 12: Bottom v iew of the demo board (not in scale)

AN1897 - APPLICATION NOTE

Figure 13: PCB Art Work (not in scale)

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AN1897 - APPLICATION NOTE

5. BILL OF MATERIALS Ref. Description Note

U1 U2 U3 U4 Q1 Q3

D1, D2, D3, D4

D5

D6, D7, D9, D10, D13

D8

D11, D12

C1, C2

C3 C4

C5, C8

C6 C7

C9 C10 C12 C13 C15 C17 C19 C20 C25 RT1

R2

R3

R4, R5, R6

R8, R9

R11

CH1

TX1

F1

J1, J2

J3 J4 J5

Photocoupler PC81 7 SHA RP VIPer22A DIP STMicroelectronics TL431 ACZ STMicroelectronics L4931 ABV33 STMicroelectronics SS9014 SS8550 1N4007 FR157 STTH102 STMicroelectronics STPS5L60 STMicroelectronics 1N5818 STMicroelectronics Y1 Capacitor 2200pF X2 Capacitor 0.1uF Electrolytic Capacitor 100uF/400V 1nF/1KV Ceramic Capacitor 47nF/ 50V Electrolytic Capacitor 47uF/50V Electrolytic Capacitor 220uF/50V Ceramic Capacitor 47pF/ 50V Electrolytic Capacitor 1000uF/16V Electrolytic Capacitor 470uF/16V Electrolytic Capacitor 100uF/10V Electrolytic Capacitor 470uF/25V Electrolytic Capacitor 470uF/25V Electrolytic Capacitor 220uF/50V Electrolytic Capacitor 220uF/16V Not fit

9.1KΩ ¼ W

100KΩ 1W 1KΩ ¼ W

5.1KΩ ¼ W 680Ω ¼ W

2.2mH Common choke EER28 transformer Fuse 1A 2pin connector 5pin connector 4pin connector 9pin connector

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AN1897 - APPLICATION NOTE

Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such i nformat ion nor f or any infr ingement of patents or other rig hts of third par ties w hich may res ults from i ts use. No license is granted by i m pl i cation or ot herwise under any pate nt or patent ri ghts of STMicroelectr oni cs. Specifications mentioned i n this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical compone nts in lif e support de vi ces or syste m s without express writt en approval of STMicr oelectronics.

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