AN2950
Application note
EVLVIPER28L-10W: 5 V/10 W, 60 kHz isolated flyback
with extra power management
Introduction
This document describes a 5 V, 2 A application with 3.3 A peak current capability of 1.9 sec,
using VIPer28, a new offline high-voltage converter from STMicroelectronics.
In some applications, an SMPS sometimes undergoes load peaks that can be two or more
times as much as the power it is supposed to deliver, though only for a short time interval
compared to the thermal time constants of the power components. Typical examples of such
loads are printers and audio systems.
In such cases, it is more cost-effective to thermally design the system for the maximum
continuous power and not for the peak power demand, which is sustained only for a limited
time window.
Such a design is possible thanks to the EPT function of the VIPer28, which allows the
designer to fix the maximum time window during which the converter is able to manage the
peak power and still maintain output voltage regulation. If the overload lasts for longer than
this time window, the converter is automatically shut down and enters auto-restart mode
until the overload is removed, so as to prevent damage to the power components.
The device has many other features such as an 800 V avalanche rugged power section,
PWM operation at 60 kHz with frequency jittering for lower EMI, a limiting current with
adjustable setpoint, an on-board soft-start, a safe auto-restart after a fault condition, and a
low standby power (< 50 mW at 265 V
AC
).
The available protections include adjustable and accurate overvoltage protection, thermal
shutdown with hysteresis and delayed overload protection.
Figure 1.
Demonstration board
April 2010
Doc ID 15494 Rev 1
1/37
www.st.com
Contents
AN2950
Contents
1
Adapter features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.1
1.2
Circuit description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2
Testing the board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
2.10
2.11
2.12
Typical board waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Regulation precision and output voltage ripple . . . . . . . . . . . . . . . . . . . . 12
Burst mode and output voltage ripple . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Light load performances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Overload protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Second OCP protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Output overvoltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
EPT function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Thermal measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
EMI measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Board layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Appendix A Test equipment and measurement of efficiency and low load
performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
A.1
Notes on input power measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
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Doc ID 15494 Rev 1
AN2950
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.
Table 14.
Table 15.
Table 16.
Table 17.
Table 18.
Table 19.
Table 20.
Electrical specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1338.0019 transformer characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Transformer pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Output voltage and VDD line-load regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Output voltage ripple. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Burst mode related output voltage ripple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Active mode efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Input voltage averaged efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Energy efficiency criteria for standard models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Energy efficiency criteria for low-voltage models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
No load input power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Energy consumption criteria for no load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Low load performance - POUT = 25 mW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Low load performance - POUT = 50 mW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Output power when the input power is 1 W . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Output overvoltage threshold at different input/output conditions. . . . . . . . . . . . . . . . . . . . 25
Temperature of key components at 115 VAC full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Doc ID 15494 Rev 1
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List of figures
AN2950
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.
Figure 45.
Figure 46.
Figure 47.
Figure 48.
Demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Application schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Transformer size and pin diagram - bottom view (pin side) . . . . . . . . . . . . . . . . . . . . . . . . . 9
Transformer size and pin diagram - electrical diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Transformer size - side view 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Transformer size - side view 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Drain current and voltage at maximum load 115 VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Drain current and voltage at maximum load 230 VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Drain current and voltage at maximum load 90 VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Drain current and voltage at maximum load 265 VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Drain current and voltage at peak load 90 VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Drain current and voltage at peak load 265 VAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Output voltage ripple 115 VIN_AC full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Output voltage ripple 230 VIN_AC full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Output voltage ripple at 115 VIN_AC no load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Output voltage ripple at 230 VIN_AC no load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Output voltage ripple at 115 VIN_AC 50 mA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Output voltage ripple at 230VIN_AC 50 mA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Efficiency vs VIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Efficiency vs load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Active mode efficiency vs VIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Input voltage averaged efficiency vs load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
ENERGY STAR® efficiency criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Pin vs VIN at low load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Pout vs VIN at Pout = 1 W . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
OLP: output short and protection tripping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
OLP: output short and protection tripping (zoom on FB pin voltage) . . . . . . . . . . . . . . . . . 21
OLP: steady state (autorestart mode). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
OLP: steady state (zoom on FB pin voltage) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
OLP: steady-state, short removal and restart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
OLP: restart after short removal (zoom) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Second OCP protection tripping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Operating with secondary winding shorted. Restart mode . . . . . . . . . . . . . . . . . . . . . . . . . 22
Operating with secondary winding shorted. Steady state . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Operating with secondary winding shorted. Steady state (zoom). . . . . . . . . . . . . . . . . . . . 23
OVP circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Output overvoltage protection at 115 VIN_AC 0.2 A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Output voltage ripple at 230 VIN_AC no load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Auto-restart mode of the overvoltage protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Auto-restart mode of the overvoltage protection (zoom) . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Normalized output OVP threshold vs load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Extra power applied and removed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Extra power applied indefinitely . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
EPT thresholds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Thermal measurements at 90 VAC full load, Tamb = 25 °C . . . . . . . . . . . . . . . . . . . . . . . 27
Average measurement of background noise (board disconnected from mains). . . . . . . . . 28
Average measurement at 115 Vac, full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Average measurements at 230 Vac, full load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4/37
Doc ID 15494 Rev 1
AN2950
Figure 49.
Figure 50.
Figure 51.
Figure 52.
Figure 53.
List of figures
Top layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Bottom layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Connection of the UUT to the wattmeter for power measurements . . . . . . . . . . . . . . . . . . 32
Suggested connection for low power measurements (switch in position 1) . . . . . . . . . . . . 33
Suggested connection for high power measurements (switch in position 2) . . . . . . . . . . . 33
Doc ID 15494 Rev 1
5/37
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