dm00053857

AN4106
Application note
EVLVIP26L-12WFN: 12 V/12 W, 60 kHz non-isolated flyback
By Mirko Sciortino
Introduction
This document describes a 12 V-1 A power supply set in non-isolated flyback topology with
the VIPER26, a new offline high-voltage converter by STMicroelectronics.
The features of the device include an 800 V avalanche rugged power section, PWM
operation at 60 kHz with frequency jittering for lower EMI, current limiting with adjustable set
point, onboard soft-start, a safe auto-restart after a fault condition and low standby power.
The available protection includes thermal shutdown with hysteresis, delayed overload
protection, and open loop failure protection. All protection is auto-restart mode.
Figure 1.
EVLVIP26L-12WFN demonstration board
EVLVIP26L-12WFN
October 2012
Doc ID 023156 Rev 1
1/39
www.st.com
Contents
AN4106
Contents
1
Adapter features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2
Circuit description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3
Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4
Transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5
Testing the board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.1
Typical waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6
Line/load regulation and output voltage ripple . . . . . . . . . . . . . . . . . . 14
7
Burst mode and output voltage ripple . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8
Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
9
Light load performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
10
Functional check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
11
10.1
Soft-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
10.2
Overload protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
10.3
Feedback loop failure protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Feedback loop calculation guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . 25
11.1
Transfer function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
11.2
Compensation procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
12
Thermal measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
13
EMI measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
14
Board layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
15
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2/39
Doc ID 023156 Rev 1
AN4106
Contents
Appendix A Test equipment and measurement of efficiency and light load
performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
A.1
Measuring input power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
16
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
17
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Doc ID 023156 Rev 1
3/39
List of figures
AN4106
List of figures
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.
Figure 15.
Figure 16.
Figure 17.
Figure 18.
Figure 19.
Figure 20.
Figure 21.
Figure 22.
Figure 23.
Figure 24.
Figure 25.
Figure 26.
Figure 27.
Figure 28.
Figure 29.
Figure 30.
Figure 31.
Figure 32.
Figure 33.
Figure 34.
Figure 35.
Figure 36.
Figure 37.
Figure 38.
Figure 39.
Figure 40.
Figure 41.
Figure 42.
Figure 43.
Figure 44.
4/39
EVLVIP26L-12WFN demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Application schematic - complete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Application schematic - simplified for VOUT ≥ 12 V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Transformer size and pin diagram, bottom view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Transformer size, side view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Transformer, pin distances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Transformer, electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Drain current and voltage at VIN = 115 VAC, full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Drain current and voltage at VIN = 230 VAC, full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Drain current and voltage at VIN = 90 VAC, full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Drain current and voltage at VIN = 265 VAC, full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Line regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Load regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Output voltage ripple at VIN = 115 VAC, full load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Output voltage ripple at VIN = 230 VAC, full load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Output voltage ripple at VIN = 115 VAC, no load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Output voltage ripple at VIN = 230 VAC, no load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Output voltage ripple at VIN = 115 VAC, IOUT = 25 mA . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Output voltage ripple at VIN = 230 VAC, IOUT = 25 mA . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Active mode efficiency vs. VIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
PIN vs. VIN at no load and light load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Efficiency at PIN = 1 W . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
PIN at POUT = 0.25 W . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Soft-start at startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Soft-start at startup (zoom) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Output short-circuit applied: OLP tripping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Output short-circuit maintained: OLP steady-state . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Output short-circuit maintained: OLP steady-state, zoom . . . . . . . . . . . . . . . . . . . . . . . . . 23
Output short-circuit removal and converter restart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Feedback loop failure protection: tripping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Feedback loop failure protection: steady-state . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Feedback loop failure protection: steady-state, zoom . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Feedback loop failure removal: converter restart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Control loop block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Thermal map at TAMB = 25 ×C, VIN = 85 VAC, full load . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Thermal map at TAMB = 25 ×C, VIN = 115 VAC, full load . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Thermal map at TAMB = 25 ×C, VIN = 230 VAC, full load . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Background noise measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Average measurement at VIN = 115 VAC, full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Average measurement at VIN = 230 VAC, full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Bottom layer & top overlay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Connections of the UUT to the wattmeter for power measurements . . . . . . . . . . . . . . . . . 34
Switch in position 1 - setting for standby measurements . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Switch in position 2 - setting for efficiency measurements . . . . . . . . . . . . . . . . . . . . . . . . . 35
Doc ID 023156 Rev 1
AN4106
List of tables
List of tables
Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Table 6.
Table 7.
Table 8.
Table 9.
Table 10.
Table 11.
Table 12.
Table 13.
Electrical specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Bill of material (simplified schematic) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Transformer characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Output voltage line-load regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Output voltage ripple at half and full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Output voltage ripple at no/light load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
No load input power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Energy consumption criteria for no load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Light load performance at POUT = 25 mW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Light load performance at POUT = 50 mW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
POUT @ PIN = 1 W . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Key components temperature @ VIN = 85 VAC /230 VAC, full load (TAMB = 25 ° C) . . . . . 29
Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Doc ID 023156 Rev 1
5/39
Adapter features
1
AN4106
Adapter features
The electrical specifications of the demonstration board are listed in Table 1.
Table 1.
Electrical specifications
Symbol
VIN
Parameter
Input voltage range
Value
90 VAC - 265 VAC
VOUT
Output voltage
12 V
IOUT
Max. output current
1A
Δ VOUT_LF
Precision of output regulation
± 5%
Δ VOUT_HF
High frequency output voltage ripple
50 mV
TAMB
Max. ambient operating temperature
60 ºC
6/39
Doc ID 023156 Rev 1
AN4106
2
Circuit description
Circuit description
The power supply is set in flyback topology. The complete schematic is given in Figure 2; a
simplified schematic for VOUT ≥12 V and the relevant BOM are given in Figure 3 and in
Table 2 respectively. The input section includes a resistor R1 and an NTC for inrush current
limiting, a diode bridge (D0) and a Pi filter for EMC suppression (C1, L2, C2). The
transformer core is a standard E20. A Transil™ clamp network (D1, D4) is used for leakage
inductance demagnetization. The output voltage value is set in a simple way through the
R3-R4 voltage divider between the output terminal and the FB pin, according to the following
formula:
Equation 1
R3 ⎞
⎛
VOUT = 3.3V ⋅ ⎜ 1 +
⎟
⎝ R4 ⎠
In fact, the FB pin is the input of an error amplifier and is an accurate 3.3 V voltage
reference. In the schematic the resistor R4 has been split into R4a and R4b in order to allow
better tuning of the output voltage value. The compensation network is connected between
the COMP pin (which is the output of the error amplifier) and the GND pin and is made up of
C7, C8 and R7. The output rectifier D3 has been selected according to the calculated
maximum reverse voltage, forward voltage drop and power dissipation and is a power
Schottky type. A resistor has been connected between the LIM and GND pins in order to
reduce the IDLIM to the value needed to supply the required output power, limiting the
stress on the power components.
At power-up the DRAIN pin supplies the internal HV startup current generator which
charges the VDD capacitor, C4, up to VDDon. At this point the Power MOSFET starts
switching, the generator is turned off and the IC is powered by the energy stored in C4. If the
nominal value of VOUT exceeds the VDDcson threshold of the VIPER26 by a small signal
diode forward voltage drop, the IC can be supplied directly from the output selecting jumper
J2 in Figure 2. In this case jumper J1 is open because the auxiliary winding of the
transformer is not needed and the schematic can be simplified, as in Figure 3. Since
VDDcsonmax = 11.5 V, the minimum value of VOUT allowing this connection is 12 V. If VOUT <
12 V, the VIPER26 must be supplied through the auxiliary winding of the transformer (J1
selected, J2 open in Figure 2), delivering to the VDD pin a voltage higher than VDDcson. The
voltage generated by the auxiliary winding increases with the load on the regulated output.
An external clamp (D5, R1) can be added in this case, in order to avoid the VDD operating
range being exceeded.
The figures and measurements in this document refer to a case in which VDD is supplied
from the output, i.e. to the simplified schematic shown in Figure 3.
Doc ID 023156 Rev 1
7/39
8/39
Doc ID 023156 Rev 1
D5
R1
C6
F
R4b
R4a
R3
NTC
t
+
C4
J1
C5
-
R7
C7
D0
FB
R2
COMP
C8
+
+
LIM
R5
CONTROL
VDD
C1
L2
D2
C2
GND
DRAIN
+
D1
D4
J2
T1
VIPER26
IC1
2
1
3
C9
5
8,9
6,7
D6
D3
C10
+
C11
+
L1
C12
+
GROUND
VOUT
Figure 2.
AC IN
AC IN
Circuit description
AN4106
Application schematic - complete
AM11547v1
Doc ID 023156 Rev 1
C6
R4b
R4a
R3
F
C4
+
NTC
C5
t
-
R7
C7
FB
+
C8
COMP
D0
+
LIM
R5
CONTROL
VDD
C1
L2
C2
GND
DRAIN
+
D1
D4
D6
VIPER26
3
1
3
5
T2
8,9
6,7
D3
C10
+
C11
+
GROUND
VOUT
Figure 3.
AC IN
AC IN
AN4106
Circuit description
Application schematic - simplified for VOUT ≥ 12 V
AM11548v1
9/39
Bill of material
AN4106
3
Bill of material
Table 2.
Bill of material (simplified schematic)
Reference
Part
NTC
2.2 Ω NTC
NTC thermistor
F
T2A 250V
2 A, 250 VAC fuse, TR5 series
Wickmann
C1
10 µF, 400 V NHG series electrolytic capacitor
Panasonic
C2
22 µF, 35 V SMG series electrolytic capacitor
Panasonic
C4
2.2 µF, 63 V electrolytic capacitor
C5
100 nF, 50 V ceramic capacitor
C6
1 nF, 50 V ceramic capacitor
C7
47 nF, 50 V ceramic capacitor
C8
2.2 nF, 50 V ceramic capacitor
C9
Manufacturer
EPCOS
Not mounted
C10
1000 µF, 16 V ultra low ESR electrolytic capacitor ZL
series
Rubycon
C11
680 µF, 16 V ultra low ESR electrolytic capacitor ZL series
Rubycon
C12
Not mounted
D0
DF06M
D1
STTH1L06
D2
Not mounted
D3
STPS3150
3 A-150 V power Schottky (output diode)
D4
1.5KE300A
Transil
D5
Not mounted
D6
1N4148
R1
Not mounted
R2
Not mounted
1 A - 600 V diode bridge
1 A - 600 V ultrafast diode
Vishay
ST
ST
ST
Small signal diode
R3
47k Ω 1% 1/4 W resistor
R4a
15k Ω 1% 1/4 W resistor
R4b
2.7k Ω 1% 1/4 W resistor
R5
33k Ω 1/4 W resistor
R7
3.3k Ω 1/4 W resistor
L1
10/39
Description
Short-circuit
Doc ID 023156 Rev 1
Fairchild
AN4106
Table 2.
Bill of material
Bill of material (simplified schematic) (continued)
Reference
Part
Description
L2
RFB0807-102
T1
1715.0049
IC1
VIPER26LN
High-voltage 60 kHz PWM
J1
Not mounted
Jumper
J2
Short-circuit
Jumper
Input filter inductor (L=1 mH, ISAT=0.3 A; DCRmax=3.4 Ω)
60 kHz switch mode transformer
Doc ID 023156 Rev 1
Manufacturer
Coilcraft
Magnetica
ST
11/39
Transformer
4
AN4106
Transformer
The characteristics of the transformer are listed in the table below:
Table 3.
Transformer characteristics
Parameter
Value
Test conditions
Manufacturer
Magnetica
Part number
1715.0049
Primary inductance
1.6 mH ±15%
Measured at 1 kHz, TAMB = 20 oC
Leakage inductance
0.74%
Measured at 10 kHz, TAMB = 20 oC
Primary to secondary turn ratio (3 - 5)/(6,7- 8,9)
5.89 ± 5%
Measured at 10 kHz, TAMB = 20 oC
Primary to auxiliary turn ratio (3 - 5)/(1 - 2)
5.89 ± 5%
Measured at 10 kHz, TAMB = 20 oC
The figures below show electrical diagram, size and pin distances (in mm) of the
transformer.
Figure 4.
Transformer size and pin diagram,
bottom view
Figure 5.
Transformer size, side view
18 MAX
3.5 MIN
AM11550v1
AM11549v1
Figure 6.
Transformer, pin distances
Figure 7.
AM11551v1
12/39
Doc ID 023156 Rev 1
Transformer, electrical diagram
AM11552v1
AN4106
Testing the board
5
Testing the board
5.1
Typical waveforms
Drain voltage and current waveforms in full load condition are shown for the two nominal
input voltages in Figure 8 and 9, and for minimum and maximum input voltage in Figure 10
and 11 respectively.
Figure 8.
Figure 9.
Drain current and voltage at
VIN = 115 VAC, full load
Drain current and voltage at
VIN = 230 VAC, full load
AM11553v1
Figure 10. Drain current and voltage at
VIN = 90 VAC, full load
AM11554v1
Figure 11. Drain current and voltage at
VIN = 265 VAC, full load
AM11555v1
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AM11556v1
13/39
Line/load regulation and output voltage ripple
6
AN4106
Line/load regulation and output voltage ripple
The output voltage of the board has been measured in different line and load condition. The
results are shown in Table 4. The output voltage is practically not affected by the line
condition.
Table 4.
Output voltage line-load regulation
VOUT
VIN [VAC]
No load
50% load
75% load
100% load
90
12.18
12.16
12.17
12.19
115
12.18
12.17
12.17
12.19
150
12.18
12.17
12.18
12.18
180
12.18
12.17
12.18
12.18
230
12.18
12.18
12.18
12.17
265
12.18
12.18
12.18
12.18
Figure 13. Load regulation
12.3
12.3
12.2
12.2
0
12.1
25%
50%
75%
12
Vout[V]
Vout[V]
Figure 12. Line regulation
90
12.1
115
230
12
265
100%
11.9
11.9
80
105
130
155
180
205
230
255
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
1
Iout[A]
VIN [VAC]
AM11557v1
AM11558v1
The ripple at the switching frequency superimposed at the output voltage has also been
measured and the results are reported in Table 5.
14/39
1.1
Doc ID 023156 Rev 1
AN4106
Table 5.
Line/load regulation and output voltage ripple
Output voltage ripple at half and full load
VOUT (mV)
VIN [VAC]
Half load
Full load
90
17
23
115
16
21
230
18
25
265
17
24
Figure 14. Output voltage ripple at
VIN = 115 VAC, full load
Figure 15. Output voltage ripple at
VIN = 230 VAC, full load
AM11559v1
Doc ID 023156 Rev 1
AM11560v1
15/39
Burst mode and output voltage ripple
7
AN4106
Burst mode and output voltage ripple
When the converter is lightly loaded, the COMP pin voltage decreases. As it reaches the
shutdown threshold, VCOMPL (1.1 V, typical), the switching is disabled and no more energy is
transferred to the secondary side. So, the output voltage decreases and the regulation loop
makes the COMP pin voltage increase again. As it rises 40 mV above the VCOMPL
threshold, the normal switching operation is resumed. This results in a controlled on/off
operation (referred to as “burst mode”) as long as the output power is so low that it requires
a turn-on time lower than the minimum turn-on time of the VIPER26. This mode of operation
keeps the frequency-related losses low when the load is very light or disconnected, making
it easier to comply with energy-saving regulations. The figures below show the output
voltage ripple when the converter is no/lightly loaded and supplied with 115 VAC and with
230 VAC respectively.
Figure 16. Output voltage ripple at
Figure 17. Output voltage ripple at
VIN = 115 VAC, no load
VIN = 230 VAC, no load
AM11562v1
AM11561v1
Figure 18. Output voltage ripple at
VIN = 115 VAC, IOUT = 25 mA
Figure 19. Output voltage ripple at
VIN = 230 VAC, IOUT = 25 mA
AM11563v1
16/39
Doc ID 023156 Rev 1
AM11564v1
AN4106
Burst mode and output voltage ripple
Table 6 shows the measured value of the burst mode frequency ripple measured in different
operating conditions. The ripple in burst mode operation is very low.
Table 6.
Output voltage ripple at no/light load
VOUT [mV]
VIN [VAC]
No load
25 mA load
90
2
3
115
2
3
230
2
4
265
3
4
Doc ID 023156 Rev 1
17/39
Efficiency
8
AN4106
Efficiency
The active mode efficiency is defined as the average of the efficiencies measured at 25%,
50%, 75% and 100% of maximum load, at nominal input voltage (VIN = 115 VAC and VIN =
230 VAC).
External power supplies (the power supplies which are contained in a separate housing
from the end-use devices they are powering) need to comply with the Code of Conduct,
version 4 "Active mode efficiency" criterion, which states an active mode efficiency higher
than 77.7% for a power throughput of 12 W.
Another standard to be applied to external power supplies in the coming years is the DOE
(Department of energy) recommendation, whose active mode efficiency requirement for the
same power throughput is 82.96%.
The presented demonstration board is compliant with both standards, as can be seen from
Figure 20, where the average efficiencies of the board at 115 VAC (87%) and at 230 VAC
(86.7%) are plotted with dotted lines, together with the above limits. In the same figure the
efficiency at 25%, 50%, 75% and 100% of load for both input voltages is also shown.
Figure 20. Active mode efficiency vs. VIN y
87
eff [%]
85
DOE limit
83
115
230
av @ 115 Vac
av @ 230 Vac
81
79
CoC4 limit
77
75
0.2
0.4
0.6
Iout[A]
0.8
1
AM11567v1
18/39
Doc ID 023156 Rev 1
AN4106
9
Light load performance
Light load performance
The input power of the converter has been measured in no load condition for different input
voltages and the results are reported in Table 7.
Table 7.
No load input power
VIN [VAC]
PIN [mW]
90
12.8
115
13.6
150
15.0
180
16.6
230
19.9
265
22.9
In version 2.0 of the Code of Conduct, version 4 program the power consumption of the
power supply when it is not loaded is also considered. The criteria for compliance are given
in the table below:
Table 8.
Energy consumption criteria for no load
Nameplate output power (Pno)
Maximum power in no load for AC-DC EPS
0 W ≤Pno ≤50 W
< 0.3 W
50 W < Pno < 250 W
< 0.5 W
The power consumption of the presented board is about ten times lower than the Code of
Conduct, version 4 limit. Even if this performance seems to be disproportionally better than
the requirements, it is worth noting that often AC-DC adapter or battery charger
manufacturers have very strict requirements about no load consumption and when the
converter is used as an auxiliary power supply, the line filter is often the main line filter of the
entire power supply which considerably increases standby consumption.
Even if the Code of Conduct, version 4 program does not have other requirements regarding
light load performance, in order to give more information the input power and efficiency of
the demonstration board also in two other light load cases is shown. Table 9 and Table 10
show the performances when the output load is 25 mW and 50 mW respectively.
Table 9.
Light load performance at POUT = 25 mW
VIN [VAC]
POUT [mW]
PIN [mW]
Efficiency (%)
90
25
47.2
53.0
115
25
48.7
51.4
150
25
51.2
48.7
180
25
54.4
45.9
230
25
59.2
42.2
265
25
65.0
38.5
Doc ID 023156 Rev 1
19/39
Light load performance
Table 10.
AN4106
Light load performance at POUT = 50 mW
VIN [VAC]
POUT [mW]
PIN [mW]
Efficiency (%)
90
50
76.4
65.4
115
50
78.4
63.8
150
50
81.7
61.2
180
50
85.1
58.7
230
50
91.6
54.6
265
50
98.0
51.0
The input power vs. input voltage for no load and light load condition (Table 7, 9 and 10) are
shown in the figure below.
Figure 21. PIN vs. VIN at no load and light load
200
0
175
25mW
Pin [mW]
150
50mW
125
100
75
50
25
0
80
105
130
155
180
205
230
255
VIN [VAC]
AM11570v1
Depending on the equipment supplied, it’s possible to have several criteria to measure the
standby or light load performance of a converter. One criterion is the measurement of the
output power when the input power is equal to one watt. In Table 11 the output power
needed to have 1 W of input power in different line conditions is given. Figure 22 shows the
output power corresponding to PIN = 1 W for different values of the input voltage.
Table 11.
20/39
POUT @ PIN = 1 W
VIN [VAC]
PIN (W)
POUT (W)
Efficiency (%)
90
1
0.837
83.7
115
1
0.827
82.7
150
1
0.826
82.6
Doc ID 023156 Rev 1
AN4106
Light load performance
Table 11.
POUT @ PIN = 1 W
VIN [VAC]
PIN (W)
POUT (W)
Efficiency (%)
180
1
0.801
80.1
230
1
0.766
76.6
265
1
0.753
75.3
Figure 22. Efficiency at PIN = 1 W
90
85
80
eff [%]
75
70
65
60
55
50
80
110
140
170
200
230
260
VIN[VAC]
AM11571v1
Another requirement (EuP lot 6) is that the input power should be less than 500 mW when
the converter is loaded with 250 mW. The converter can satisfy even this requirement, as
shown in Figure 23.
Figure 23. PIN at POUT = 0.25 W
0.5
0.45
PIN [W]
0.4
0.35
0.3
0.25
80
110
140
170
Vin[V]
Doc ID 023156 Rev 1
200
230
260
AM11571v2
21/39
Functional check
10
Functional check
10.1
Soft-start
AN4106
At startup the current limitation value reaches IDLIM after an internally set time, tSS, whose
typical value is 8.5 msec. This time is divided into 16 time intervals, each corresponding to a
current limitation step progressively increasing. In this way the drain current is limited during
the output voltage increase, therefore reducing the stress on the secondary diode. The softstart phase is shown in Figure 24 and 25.
Figure 24. Soft-start at startup
Figure 25. Soft-start at startup (zoom)
AM11572v1
10.2
AM11573v1
Overload protection
In case of overload or short-circuit (see Figure 26), the drain current reaches the IDLIM
value (or the one set by the user through the RLIM resistor). Every cycle that this condition
is met, a counter is incremented. If the fault is maintained continuously for the time tOVL (50
msec typical, set internally), the overload protection is tripped, the power section is turned
off and the converter is disabled for a tRESTART time (1 s typical). After this time has elapsed,
the IC resumes switching and, if the short is still present, the protection occurs indefinitely in
the same way (Figure 27). This ensures restart attempts of the converter with low repetition
rate, so that it works safely with extremely low power throughput and avoids overheating of
the IC in case of repeated overload events.
Moreover, every time the protection is tripped, the internal soft-start function (Figure 25) is
invoked, in order to reduce the stress on the secondary diode.
After the short removal, the IC resumes working normally. If the short is removed during tSS
or tOVL, i.e. before the protection tripping, the counter is decremented on a cycle-by-cycle
basis down to zero and the protection is not tripped.
If the short-circuit is removed during tRESTART, the IC waits for the tRESTART period to elapse
before resuming switching (Figure 29).
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AN4106
Functional check
Figure 26. Output short-circuit applied: OLP
tripping
Figure 27. Output short-circuit maintained:
OLP steady-state
Output is shorted here
tRESTART
Normal
operation
AM11575v1
AM11574v1
Figure 28. Output short-circuit maintained:
OLP steady-state, zoom
tSS
Figure 29. Output short-circuit removal and
converter restart
tOVL
tRESTART
Normal
operation
Output short is
removed here
AM11576v1
10.3
AM11577v1
Feedback loop failure protection
As the loop is broken (R4 = R4a+R4b shorted or R3 open), the output voltage VOUT
increases and the VIPER26 runs at its maximum current limitation. The VDD pin voltage
increases as well, because it is linked to the VOUT voltage either directly or through the
auxiliary winding, depending on the cases.
If the VDD voltage reaches the VDDclamp threshold (23.5 V min.) in less than 50 msec, the IC
is shut down by open loop failure protection (see Figure 30 and 31), otherwise by OLP, as
described in the previous section. The breaking of the loop has been simulated by shorting
the low-side resistor of the output voltage divider, R4 = R4a+R4b. The same behavior can
be induced opening the high-side resistor, R3.
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Functional check
AN4106
The protection acts in auto-restart mode with tRESTART = 1 s (Figure 31). As the fault is
removed, normal operation is restored after the last tRESTART interval has been completed
(Figure 33).
Figure 30. Feedback loop failure protection:
Figure 31. Feedback loop failure protection:
tripping
steady-state
Fault is applied here
VDD reaches VDDCLAMP
< tOVL
Normal
operation
tRESTART
AM11578v1
Figure 32. Feedback loop failure protection:
steady-state, zoom
AM11579v1
Figure 33. Feedback loop failure removal:
converter restart
Fault is removed here
tRESTART
Normal
operation
< tOVL
AM11580v1
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AM11581v1
AN4106
Feedback loop calculation guidelines
11
Feedback loop calculation guidelines
11.1
Transfer function
The set PWM modulator + power stage is indicated with G1(f), while C(f) is the “controller”,
i.e. the network which is in charge to ensure the stability of the system.
Figure 34. Control loop block diagram
AM11582v1
The mathematical expression of the power plant G1(f) is the following:
Equation 2
j ⋅2⋅π ⋅ f
j⋅ f
VOUT ⋅ (1 +
)
VOUT ⋅ (1 +
)
ΔVOUT
fz
z
=
G 1 (f) =
=
j ⋅ 2 ⋅π ⋅ f
j⋅ f
ΔI pk
Ipkp ( fsw,Vdc) ⋅ (1 +
) Ipkp ( fsw, Vdc ) ⋅ (1 +
)
p
fp
where VOUT is the output voltage, Ipkp is the primary peak current, fp is the frequency of the
pole due to the output load:
Equation 3
fp =
1
π ⋅ C OUT ·(R OUT + 2ESR)
and fz the frequency of the zero due to the ESR of the output capacitor:
Equation 4
fz =
1
2 ⋅π ⋅ C OUT ·ESR
The mathematical expression of the compensator C(f) is:
Doc ID 023156 Rev 1
25/39
Feedback loop calculation guidelines
AN4106
Equation 5
C(f )=
ΔI pk
ΔV OUT
=
C0
⋅
H COMP
1+
f ⋅j
fZc
⎛
f ⋅j⎞
2 ⋅ π ⋅ f ⋅ j ⋅ ⎜⎜1 +
⎟
fPc ⎟⎠
⎝
where (with reference to the schematic of Figure 2):
Equation 6
C0 = −
Gm
R4
⋅
C 7 + C 8 R3 + R 4
Equation 7
fZc =
1
2 ⋅ π ⋅ R7 ⋅ C7
Equation 8
fPc =
C7 + C 8
2 ⋅ π ⋅ R7 ⋅ C7 ⋅ C8
are to be chosen with the purpose to ensure the stability of the overall system. Gm = 2 mA/V
(typical) is the VIPER26 transconductance.
11.2
Compensation procedure
The first step is to choose the pole and zero of the compensator and the crossover
frequency, for instance:
●
fZc = fp/2
●
fPc = fz
●
fcross = fcross_sel ≤fsw/10.
G1(fcross_sel) can be calculated from equation (2) and, being by definition
| C(fcross_sel)*G1(fcross_sel)| = 1, C0 can be calculated as follows:
Equation 9
2 ⋅ π ⋅ fcross _ sel ⋅ j ⋅ 1 +
C0 =
1+
fcross _ sel ⋅ j
fPc
fcross _ sel ⋅ j
fZc
⋅
HCOMP
G1( fcross _ sel )
At this point the Bode diagram of G1(f)*C(f) can be plotted, in order to check the phase
margin for the stability. If the margin is not high enough, another choice should be made for
26/39
Doc ID 023156 Rev 1
AN4106
Feedback loop calculation guidelines
fZc, fPc and fcross_sel, and the procedure repeated. When the stability is ensured, the next
step is to find the values of the schematic components, which can be calculated, using the
above formulas, as follows:
Equation 10
R5 =
R6
V OUT
−1
3. 3V
Equation 11
C8 =
fZc Gm
R4
⋅
⋅
fPc C 0 R 4 + R 3
Equation 12
⎛ fPc ⎞
C7 = C8 ⋅ ⎜⎜
− 1⎟⎟
⎝ fZc ⎠
Equation 13
R7 =
C 7 + C8
2 ⋅ π ⋅ fPc ⋅ C7 ⋅ C8
Doc ID 023156 Rev 1
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Thermal measurements
12
AN4106
Thermal measurements
A thermal analysis of the board at full load condition,@ TAMB = 25 ° C has been performed
using an IR camera. The worst case is VIN = 85 VAC, but also the nominal input voltage
cases (VIN = 115 VAC and VIN = 230 VAC) have been considered. The results are shown in
Figure 35, 36 and 37 and summarized in Table 12.
Figure 35. Thermal map at TAMB = 25 ° C, VIN = 85 VAC, full load
AM11583v1
Figure 36. Thermal map at TAMB = 25 ° C, VIN = 115 VAC, full load
AM11584v1
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Doc ID 023156 Rev 1
AN4106
Thermal measurements
Figure 37. Thermal map at TAMB = 25 ° C, VIN = 230 VAC, full load
AM11585v1
Table 12.
Key components temperature @ VIN = 85 VAC /230 VAC, full load (TAMB = 25 ° C)
T [° C ]
Reference
Point
VIN = 85 VAC
VIN = 230 VAC
A
72.2
55.2
VIPER26
B
66.6
63.4
Output diode
C
46.6
46.4
Transformer
D
51.5
34.9
Diode bridge
E
50.0
32.6
Thermistor
F
41.9
33.4
Transil
Doc ID 023156 Rev 1
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EMI measurements
13
AN4106
EMI measurements
A pre-compliance test to EN55022 (Class B) European normative has been performed
using an EMC analyzer and an LISN. First of all, a measurement of the background noise
(board disconnected from the mains) was performed and is reported in Figure 38.
Then the average EMC measurements at 115 VAC/full load and 230 VAC/full load were
performed and the results are shown in Figure 39 and 40.
Figure 38. Background noise measurement
Figure 39. Average measurement at VIN = 115 VAC, full load
30/39
Doc ID 023156 Rev 1
AN4106
EMI measurements
Figure 40. Average measurement at VIN = 230 VAC, full load
Doc ID 023156 Rev 1
31/39
Board layout
14
AN4106
Board layout
Here below the board layout:
Figure 41. Bottom layer & top overlay
32/39
Doc ID 023156 Rev 1
AN4106
15
Conclusions
Conclusions
The VIPER26 allows a simple design of a non-isolated converter with few external
components. In this document a non-isolated flyback has been described and
characterized. Special attention has been given to light load performance, confirmed as very
good by bench analysis. Efficiency has been compared to the requirements of the Code of
Conduct, version 4 program (version 2.0) for an external AC-DC adapter with very good
results in that the measured active mode efficiency is always higher with respect to the
minimum required.
Doc ID 023156 Rev 1
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Test equipment and measurement of efficiency and light load performance
Appendix A
AN4106
Test equipment and measurement of
efficiency and light load performance
The converter input power has been measured using a wattmeter. The wattmeter measures
simultaneously the converter input current (using its internal ammeter) and voltage (using its
internal voltmeter). The wattmeter is a digital instrument so it samples the current and
voltage and converts them to digital forms. The digital samples are then multiplied giving the
instantaneous measured power. The sampling frequency is in the range of 20 kHz (or higher
depending on the instrument used). The display provides the average measured power,
averaging the instantaneous measured power in a short period of time (1 sec typ.).
Figure 42 shows how the wattmeter is connected to the UUT (unit under test) and to the AC
source and the wattmeter internal block diagram.
Figure 42. Connections of the UUT to the wattmeter for power measurements
Switch
1
WATT METER
U.U.T
(Unit Under test)
Voltmeter
V
+
Multiplier
A
X
2
Ammeter
AC
SOURCE
INPUT
OUTPUT
AVG
DISPLAY
AM11590v1
An electronic load has been connected to the output of the power converter (UUT), allowing
the converter load current to be set and measured, while the output voltage has been
measured by a voltmeter. The output power is the product between load current and output
voltage. The ratio between the output power, calculated as previously stated, and the input
power, measured by the wattmeter, is the converter’s efficiency, which has been measured
in different input/output conditions.
A.1
Measuring input power
With reference to Figure 42, the UUT input current causes a voltage drop across the
ammeter’s internal shunt resistance (the ammeter is not ideal as it has an internal
resistance higher than zero) and across the cables connecting the wattmeter to the UUT.
If the switch of Figure 42 is in position 1 (see also the simplified scheme of Figure 43), this
voltage drop causes an input measured voltage higher than the input voltage at the UUT
input that, of course, affects the measured power. The voltage drop is generally negligible if
the UUT input current is low (for example when we are measuring the input power of UUT in
light load condition).
34/39
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AN4106
Test equipment and measurement of efficiency and light load performance
Figure 43. Switch in position 1 - setting for standby measurements
Wattmeter
Ammeter
AC
SOURCE
~
V
A
+
U.U.T.
AC
INPUT
-
UUT
Voltmeter
AM11591v1
In the case of high UUT input current (i.e. for measurements in heavy load conditions), the
voltage drop can be relevant compared to the UUT real input voltage. If this is the case, the
switch in Figure 42 can be changed to position 2 (see simplified scheme of Figure 44) where
the UUT input voltage is measured directly at the UUT input terminal and the input current
does not affect the measured input voltage.
Figure 44. Switch in position 2 - setting for efficiency measurements
Wattmeter
A
AC
SOURCE
Ammeter
~
V
+
-
U.U.T.
AC
INPUT
UUT
Voltmeter
AM11592v1
On the other hand, the position of Figure 44 may introduce a relevant error during light load
measurements, when the UUT input current is low and the leakage current inside the
voltmeter itself (which is not an ideal instrument and doesn't have infinite input resistance) is
not negligible. This is the reason why it is better to use the setting of Figure 43 for light load
measurements and Figure 44 for heavy load measurements.
If it is not clear which measurement scheme has the lesser effect on the result, try with both
and register the lower input power value.
As noted in IEC 62301, instantaneous measurements are appropriate when power readings
are stable. The UUT is operated at 100% of nameplate output current output for at least 30
Doc ID 023156 Rev 1
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Test equipment and measurement of efficiency and light load performance
AN4106
minutes (warm-up period) immediately prior to conducting efficiency measurements. After
this warm-up period, the AC input power is monitored for a period of 5 minutes to assess the
stability of the UUT. If the power level does not drift by more than 5% from the maximum
value observed, the UUT can be considered stable and the measurements can be recorded
at the end of the 5-minute period. If AC input power is not stable over a 5-minute period, the
average power or accumulated energy is measured over time for both AC input and DC
output.
Some wattmeter models allow integration of the measured input power in a time range and
then measure the energy absorbed by the UUT during the integration time. The average
input power is calculated dividing by the integration time itself.
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AN4106
16
References
References
–
Code of Conduct on Energy Efficiency of External Power Supplies, Version 4.
–
VIPER26 datasheet.
Doc ID 023156 Rev 1
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Revision history
17
AN4106
Revision history
Table 13.
38/39
Document revision history
Date
Revision
16-Oct-2012
1
Changes
Initial release.
Doc ID 023156 Rev 1
AN4106
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