AN2811
Application note
3.5 W non-isolated offline constant-current LED driver
based on VIPER17
Introduction
High brightness LEDs are becoming a prominent source of lighting. Compared to
conventional incandescent bulbs, high brightness LEDs (light emitting diodes) have
advantages in higher light efficacy, much longer life and faster reaction time in a smaller
profile. Since LEDs cannot sustain high voltage stress directly from an AC source, providing
a reliable constant-current source to drive LEDs becomes fundamental. This solution
provides even luminosity, reliability, the highest efficacy and the longest operating life for
LEDs.
This application note describes the non-isolated offline constant-current driver based on the
VIPER17HN (high frequency version). This solution operates with an AC line input range
from 176 V to 264 VAC and provides 500 mA constant current from a 7 VDC source. It can
illuminate two LEDs in series.
This device is an offline converter with an 800 V rugged power section, a PWM control,
twice the level of overcurrent protection, overvoltage and overload protections, hysteretic
thermal protection, soft-start and also safe auto-restart after any fault condition removal.
The embedded brownout function protects this switch mode power supply in case the main
input voltage falls below the specified minimum level for this system.
Figure 1.
STEVAL-ILL017V1 demonstration board
June 2009
Doc ID 14904 Rev 1
1/25
www.st.com
Contents
AN2811
Contents
1
2
Safety instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Design considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1
Selected topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3
General circuit description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1
3.2
3.3
3.4
Schematic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
PCB layout view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Transformer design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4
5
6
7
8
Test results and waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Connection of AC line and LED lamp to the demonstration board . . 21
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2/25
Doc ID 14904 Rev 1
AN2811
List of tables
List of tables
Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Basic electrical characteristics of flyback transformer (T1). . . . . . . . . . . . . . . . . . . . . . . . . 11
Bobbin dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Doc ID 14904 Rev 1
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List of figures
AN2811
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.
STEVAL-ILL017V1 demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Conventional buck converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Modified buck converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Flyback converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Schematic diagram of demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Top view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Bottom view with SMD parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Winding structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Bobbin outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Efficiency versus input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Standby power versus input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Vin and Iin at 176 VAC, one LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Vin and Iin at 176 VAC, two LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Vin and Iin at 264 VAC, one LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Vin and Iin at 264 VAC, two LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Inrush current at LINE IN, one LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Inrush current at LINE IN, two LEDs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Vds and Id at 176 VAC, one LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Vds and Id at 176 VAC, two LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Vds and Id at 264 VAC, one LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Vds and Id at 264 VAC, two LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Vo and Io at 176 VAC, one LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Vo and Io at 176 VAC, two LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Vo and Io at 264 VAC, one LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Vo and Io at 264 VAC, two LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Startup of Vo and Io at 176 VAC, one LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Startup of Vo and Io at 176 VAC, two LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Startup of Vo and Io at 264 VAC, one LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Startup of Vo and Io at 264 VAC, two LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Vdd and Vds at 264 VAC, output in short-circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Io at 264 VAC, output in short-circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Vdd and Vds at 264 VAC, output in open-circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Startup of Vdd and Vds at 264 VAC, output in open-circuit . . . . . . . . . . . . . . . . . . . . . . . . 20
Completed demonstration board connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Connection of AC line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Connection of LED lamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
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Doc ID 14904 Rev 1
AN2811
Safety instructions
1
Safety instructions
Warning:
The demonstration board must be used in a suitable
laboratory by only qualified personnel who are familiar with
the installation, use, and maintenance of electrical systems.
Intended use
The demonstration board is a component designed for demonstration purposes only, and
shall be used neither for domestic installation nor for industrial installation. The technical
data as well as the information concerning the power supply and working conditions shall be
taken from the documentation included with the demonstration board and strictly observed.
Installation
The installation of the demonstration board shall be taken from the present document and
strictly observed. The components must be protected against excessive strain. In particular,
no components are to be bent, or isolating distances altered during the transportation,
handling or usage. The demonstration board contains electro-statically sensitive
components that are prone to damage through improper use. Electrical components must
not be mechanically damaged or destroyed (to avoid potential risks and health injury).
Electrical connection
Applicable national accident prevention rules must be followed when working on the mains
power supply. The electrical installation shall be completed in accordance with the
appropriate requirements (e.g. cross-sectional areas of conductors, fusing, and PE
connections).
Board operation
A system architecture which supplies power to the demonstration board shall be equipped
with additional control and protective devices in accordance with the applicable safety
requirements (e.g. compliance with technical equipment and accident prevention rules).
Doc ID 14904 Rev 1
5/25
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