ST AN2929 Application note

AN2929

Application note

Wide range [90 V - 265 V] input, 5 V - 12 W output VIPER27LN demonstration board with improved standby performance

Introduction

In consumer applications such as LCD or plasma TVs, some models of DVD recorders, settop boxes with hard disk, as well as desktop computers, the power supply often includes two modules: the main power supply that provides most of the power and is off when the application is in standby mode and the auxiliary power supply that provides energy for specific peripherals such as USB ports, remote receivers, and modems.

The auxiliary power supply is also on when the application is in standby mode and it is often required that its input power be as low as possible. The demonstration board presented in this application note meets the specification of a wide range of auxiliary power supplies for these applications and is optimized for very low standby consumption, helping to meet the most stringent energy-saving requirements.

Figure 1. VIPER27LN demonstration board

April 2011

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www.st.com

Contents	AN2929

Contents

1	Board description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		5
	1.1	Electrical specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	5
	1.2	Schematic and bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	5
	1.3	Transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	7

2	Testing the board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		. 9
	2.1	Typical board waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	9
	2.2	Precision of the regulation and output voltage ripple . . . . . . . . . . . . . . . .	10
	2.3	Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	13
	2.4	Light-load performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	17
	2.5	Overload protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	21
	2.6	Secondary winding short-circuit protection . . . . . . . . . . . . . . . . . . . . . . .	22
	2.7	Output overvoltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	24
	2.8	Brownout protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	26
	2.9	EMI measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	29
3	Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		30
4	References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		30
5	Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		31

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AN2929	List of figures

List of figures

Figure 1.	VIPER27LN demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. 1
Figure 2.	Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. 5
Figure 3.	Transformer size. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	8
Figure 4.	Transformer size and pin diagram [inches (mm)] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	8
Figure 5.	Drain current and voltage at full load 115 VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	9
Figure 6.	Drain current and voltage at full load 230 VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	9
Figure 7.	Drain current and voltage at full load 90 VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	9
Figure 8.	Drain current and voltage at full load 265 VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	9
Figure 9.	Output voltage ripple 115 VINAC full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	11
Figure 10.	Output voltage ripple 230 VINAC full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	11
Figure 11.	Output voltage ripple 115 VINAC at no load (burst mode) . . . . . . . . . . . . . . . . . . . . . . . . . .	12
Figure 12.	Output voltage ripple 230 VINAC 50 mA at no load (burst mode) . . . . . . . . . . . . . . . . . . . .	12
Figure 13.	Efficiency vs. VIN. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	14
Figure 14.	Efficiency vs. load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	14
Figure 15.	Active mode efficiency vs. VIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	15
Figure 16.	Input voltage averaged efficiency vs. load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	16
Figure 17.	ENERGY STAR® efficiency criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	17
Figure 18.	Input power vs. input voltage for different loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	19
Figure 19.	Average switching frequency vs. input voltage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	19
Figure 20.	Output power vs. input voltage with input power of 1 W. . . . . . . . . . . . . . . . . . . . . . . . . . .	20
Figure 21.	Output short-circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	21
Figure 22.	Operation with output shorted. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	22
Figure 23. 2nd OCP tripping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		23
Figure 24.	Operating with secondary winding shorted - restart mode . . . . . . . . . . . . . . . . . . . . . . . . .	23
Figure 25.	OVP circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	24
Figure 26.	OVP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	25
Figure 27.	Jumper J7 setting, brownout disabled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	26
Figure 28.	Jumper J7 setting, brownout enabled. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	26
Figure 29.	Brownout protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	26
Figure 30.	Input AC voltage steps from 90 VAC to 75 VAC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	28
Figure 31.	Input voltage steps from 90 VAC to 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	28
Figure 32.	115 VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	29
Figure 33.	230 VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	29

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List of tables	AN2929

List of tables

Table 1. Electrical specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Table 2. Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Table 3. Transformer characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Table 4. Output voltage and VDD line-load regulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Table 5. Output voltage ripple. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Table 6. Burst mode related output voltage ripple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Table 7. Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Table 8. Active mode efficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Table 9. Line voltage averaged efficiency vs. load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Table 10. Energy efficiency criteria for standard models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Table 11. Energy efficiency criteria for low-voltage models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Table 12. No-load input power (no brownout) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Table 13. Energy consumption criteria for no load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Table 14. Low-load performance POUT = 25 mW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Table 15. Low-load performance POUT = 50 mW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Table 16. Output power when the input power is 1 W . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Table 17. Input and output load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Table 18. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

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AN2929	Board description

1 Board description

1.1Electrical specifications

The electrical specifications of the VIPER27LN demonstration board are listed in Table 1.

Table 1.	Electrical specifications
Symbol	Parameter	Value	Unit
VIN	Input voltage range	[90VRMS; 265VRMS]	V
VOUT	Output voltage	5	V
IOUT	Max output current	2.4	A
VOUT_LF	Precision of output regulation	±5%
VOUT_HF	High-frequency output voltage ripple	50	mV
TA	Max ambient operating temperature	60	°C

1.2Schematic and bill of material

The schematic of the board is shown in Figure 2. Table 2 gives the list of components (bill of material).

Figure 2.

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Board description				AN2929
	Table 2.	Bill of material
	Reference	Part	Description	Manufacturer
	BR1	DF06M	600 V 1 A diodes bridge	Fairchild \ General
				Semiconductor
	C1, C13		22 nF X2 capacitor	Evox Rifa
	C3		450 V 33 µF electrolytic capacitor
	C4		35 V 22 µF electrolytic capacitor
	C5	Not mounted	Not mounted
	C6		25 V ceramic capacitor
	C7		25 V ceramic capacitor
	C8		Y1 2.2 nF capacitor
	C9, C14	16 V ZL 1000 µF 10X20	1000 µF 16 V electrolytic capacitor	Rubycon
	C10	16 V 100 µF YK	100 µF 16 V YK rubycon	Rubycon
	C11, C12	10 nF	25 V ceramic capacitor
	D1	BAT46	Diode	STMicroelectronics
	D2	1N4148	Diode
	D3	STTH1L06	Diode	STMicroelectronics
	D4	STPS745	Diode	STMicroelectronics
	D5	1.5KE250	Transil	STMicroelectronics
	D6	BZX79-C18	Zener diode	NXP
	F1	TR5 250 V 1 A	Fuse
	L1		3.3uH
	NTC1	B57236S160M	16 Ω NTC	EPCOS
	OPTO1	PC817	Opto coupler	Sharp
	R1		3.3 Ω axial resistor
	R16, R17		1600 kΩ 1% axial resistor
	R3		56 kΩ 1% axial resistor
	R6		12 kΩ axial resistor
	R8		120 kΩ 1% axial resistor
	R9		39 kΩ 1% resistor
	R10		270 kΩ axial resistor
	R14		220 kΩ 1% axial resistor
	R12		27 kΩ axial resistor
	R13		1 kΩ axial resistor
	R19		120 Ω axial resistor
	R20		Heatsink

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AN2929				Board description
	Table 2.	Bill of material (continued)
	Reference	Part	Description	Manufacturer
	T1	750871111	Switch-mode power transformer	Würth Elektronik
	T2	BU15-4530R4BL	Common-mode choke	Coilcraft
	U1	VIPER27LN	Offline high-voltage converters	STMicroelectronics
	VR1	TS431AIZ-AP	Voltage reference	STMicroelectronics

1.3Transformer

The transformer characteristics are listed in the table below.

	Table 3.	Transformer characteristics
		Properties	Test condition	Value
	Manufacturer			Würth Elektronik
	Part number			750871111
	Primary inductance		Measured at 10 kHz 0.1 V	1.7 mH ± 10%
	Leakage inductance		Measured at 100 kHz 0.1 V	60 μH
	Primary-to-secondary turn		Measured at 10 kHz 0.1 V	13.5 ± 3%
	ratio (6 - 4)/(7, 9 – 12, 14)
	Primary-to-auxiliary turn		Measured at 10k Hz 0.1 V	5.19 ± 3%
	ratio (6 - 4)/(3 - 1)
		Insulation	Primary to secondary	4 kV

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Board description	AN2929

The figures below show the size and pin distances (inches and [mm]) of the transformer.

Figure 3. Transformer size

(a) Top view	(b) Bottom view

Figure 4. Transformer size and pin diagram [inches (mm)]

(a) Pins distances			(b) Electrical diagram

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AN2929	Testing the board

2 Testing the board

2.1Typical board waveforms

Drain voltage and current waveforms were captured for the two nominal input voltages and for the minimum and the maximum voltage of the converter’s input operating range.

Figure 5 and Figure 6 show the drain current and the drain voltage waveforms at the nominal input voltages of 115 VAC and 230 VAC when the load is the maximum (2.4 A). Figure 7 and Figure 8 show the same waveforms for the same load condition, but for the minimum (90 VAC) and the maximum (265 VAC) input voltages.

The converter is designed to operate in continuous conduction mode (in full-load condition) at low line. CCM (continuous conduction mode) allows reducing the root mean square current values at the primary side in the power switch inside the VIPER27LN and at the secondary side in the output diode (D4) and in the output capacitors (C9 and C14). Reducing RMS currents means reducing the power dissipation (mainly in the VIPER27LN) and the stress on these components.

Figure 5. Drain current and voltage at Figure 6.		Drain current and voltage at
full load 115 VAC		full load 230 VAC

Figure 7. Drain current and voltage at Figure 8.		Drain current and voltage at
full load 90 VAC		full load 265 VAC

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Testing the board	AN2929

2.2Precision of the regulation and output voltage ripple

The output voltage of the board was measured in different line and load conditions (see Table 4). The output voltage is practically not affected by the line condition. The VDD voltage was also measured to verify that it is inside the operating range of the device.

Table 4.	Output voltage and VDD line-load regulation
VINAC (V)		No load		Half load		Full load
		VOUT (V)	VDD (v)	VOUT (V)	VDD (V)	VOUT (V)	VDD (V)
90		5.05	9.79	5.05	18.9	5.04	19.8
115		5.05	9.71	5.05	18.9	5.04	19.7
230		5.05	9.37	5.05	18.8	5.04	19.6
265		5.05	9.22	5.05	18.8	5.04	19.6

In a dual-output flyback converter, when just one output is regulated, the unregulated output does not rigorously respect the turn ratio. The unregulated output voltage value depends not only on the turn ratio but also, approximately, from the output current ratio (output current of the regulated output divided by the output current of the unregulated output).

As confirmed from the results in Table 4, the VDD voltage (unregulated auxiliary output) increases as the load on the regulated output increases. In order to avoid that the VDD voltage exceeds its operating range, an external clamp was used (D6, R19). See schematic in Figure 2.

The ripple at the switching frequency superimposed at the output voltage was also measured and the results are given in Table 5. The board is provided with an LC filter for cleaner output voltage. The high-frequency voltage ripple across capacitor C9 (VOUT_FLY), which is the output capacitor of the flyback converter before the LC filter, was also measured to verify the effectiveness of the LC filter and to provide complete results.

Table 5.	Output voltage ripple
VINAC (VRMS)			Half load			Full load
		VOUT (mV)		VOUT_FLY (mV)	VOUT (mV)		VOUT_FLY (mV)
90		25		275	40		172
115		26		275	37		201
230		26		273	36		194
265		25		272	36		195

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