cd00204388

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
!-V
June 2009
Doc ID 14904 Rev 1
1/25
www.st.com
Contents
AN2811
Contents
1
Safety instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2
Design considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1
3
Selected topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
General circuit description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1
Schematic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2
Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.3
PCB layout view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.4
Transformer design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4
Test results and waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5
Connection of AC line and LED lamp to the demonstration board . . 21
6
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
7
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
8
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2/25
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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
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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.
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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
Doc ID 14904 Rev 1
AN2811
1
Safety instructions
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
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Design considerations
AN2811
2
Design considerations
2.1
Selected topology
This is a 500 mA constant-current source conversion from 176 VAC ~ 264 VAC line input.
The specifications shown in Table 1 are for refrigerator lighting usage.
Table 1.
Specifications
Parameter
Value
AC input
220 VAC ± 20%
Output current
500 mA
Output voltage
7 V max
Dimensions
30 mm x 30 mm
Isolation
Not required
Topology
Constant-current source
According to the specifications the maximum operating power is 3.5 watts. No power factor
correction circuit is required. Therefore, both buck and flyback topologies are suitable for this
application. Figure 2 shows the conventional buck converter while Figure 4 illustrates the
flyback converter. To convert high voltage to low voltage, a conventional buck converter just
requires a few components. Output current ripple is small due to Vout obtained from
inherent filter L1 and C1, thus the voltage and current stresses on these power components
are small. In order to properly drive the MOSFET (Q1), a controller and an additional
transformer are required. Additional winding with L1 to bias Q1 as well as a feedback current
to manage output in constant-current mode are needed.
Figure 2.
Conventional buck converter
!-V
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AN2811
Design considerations
Figure 3.
Modified buck converter
!-V
For ease in driving Q1 using a conventional buck converter, a modified buck converter has
been introduced as shown in Figure 3. Such topology is widely used to drive LEDs. With this
modified solution, the MOSFET is no longer floating. In this case the output (Vout) is not
connected to ground, and it becomes quite difficult to sense the output current in the output
stage directly. Compared to a buck converter, the flyback converter may be the better
choice. Figure 4 shows the typical circuit of a flyback converter.
Figure 4.
Flyback converter
!-V
The auxiliary winding can be added to the transformer (T1) to provide bias for Q1. Unlike the
buck converter, T1 provides isolation between Vin and Vout. Since such isolation is not
required for this application, a current sense resistor can be placed across the primary
ground and negative polarity of Vout. Thus, Vout shares the same primary ground. In this
topology, the MOSFET is not floating. Thanks to VIPer17 the board is built with a highperformance low-voltage controller chip with an 800 V avalanche rugged power MOSFET.
Designed with VIPer17, only a few external components are required which allows a smaller
profile in the design.
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General circuit description
AN2811
3
General circuit description
3.1
Schematic diagram
Figure 5 shows the complete schematic diagram of the demonstration board. It consists of
an input full-bridge rectifier with filtering circuit, flyback converter and output stage.
Figure 5.
Schematic diagram of demonstration board
AM01057v1
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AN2811
General circuit description
Referring to the schematic diagram in Figure 5, fuse1 is the input fuse to prevent hazards if
the system current exceeds the fuse rating. D1 is the bridge rectifier to convert AC to DC.
The filter is formed by C11, L2 and C3 that are used to attenuate the high frequency
harmonic interference. T1 is the flyback transformer and U1 is formed by the PWM controller
and output MOSFET. The auxiliary winding (pin 5 and 6) and diode D5 provide bias supply
for each control circuit. The output stage includes D6, C9 and C13. R9 and R12 are the
output current sense resistors providing current sense signal. These are connected in
parallel to share the power dissipation.
The constant-current control circuit consists of U2, Q1, U1 and some passive components.
The output current sense signal feeds to OP amp in U2. R7 and C7 consist of the
compensation network for the output signal of U2 in order to properly drive Q1. The 0.3 V
reference voltage on pin 6 of U2 is obtained by voltage divider R11 and R10. The collector
junction of Q1 is connected to the feedback pin of U1 and completes the feedback loop.
The output voltage is indirectly monitored by the auxiliary winding (pin 5 and 6 of T1) and
feedback to pin 3 of U1 through R1 and R4. Once the voltage at pin 3 of U1 exceeds 3 V, U1
shuts down, then enters the auto-restart mode. Thanks to U1, which includes an overload
protection function, if the LED is absent in the application (no load), this solution provides a
safeguard. The LED and the application board are both fully protected.
3.2
Bill of material
Table 2.
Bill of material
Name
Value
Rated
Type
C1
1 nF
25 V
Ceramic cap [0603]
C2, C8
100 nF
25 V
Ceramic cap [0603]
C3, C11
2.2 μF
400 V
Al elcap CAPPR3.5-8X12
C4
56 nF
25 V
Ceramic cap [0603]
C5, C12
10 μF
25 V
Al elcap CAPPR2-5X11
C6
2.2 nF
25 V
Ceramic cap [0603]
C7
12 nF
25 V
Ceramic cap [0603]
C9
220 μF
16 V
Al elcap CAPPR3.5-8X11.5
C10
470 pF
25 V
Ceramic cap [0603]
C13
1 μF
25 V
Ceramic cap [0805]
D1
MB6S PKG30 E3
1 A 600 V bridge rectifier
Vishay
D3
BAT46JFILM
Small signal Schottky diode STMicroelectronics [SOD323]
D5
STTH1R06A
1 A 600 V ultrafast rectifier
STMicroelectronics [SMA]
D6
STPS2H100A
2 A 100 V Schottky rectifier
STMicroelectronics [SMA]
Fuse1
500 mA 250 V
Fuse_5_8.5*8_Bel
L2
LPS3314-105ML
1 mH, 0.1 A
Inductor, Coilcraft L_LP3314
Q1
BC817-40
NPN general-purpose
transistor
[SOT-23]
R1
240 kΩ
1%
Resistor [0603]
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General circuit description
Table 2.
AN2811
Bill of material (continued)
Name
Value
Rated
Type
R2
6.8 kΩ
1%
Resistor [0603]
R3
100 kΩ
1%
Resistor [0603]
R4
56 kΩ
1%
Resistor [0603]
R5
10 kΩ
1%
Resistor [0603]
R6
10 Ω
1%
Resistor [0603]
R7
82 kΩ
1%
Resistor [0603]
R8
3 kΩ
1%
Resistor [0603]
R9, R12
1.2 Ω
1%
Resistor [1206]
R10
3.3 kΩ
1%
Resistor [0603]
R11
24 kΩ
1%
Resistor [0603]
R13
2.7 kΩ
1%
Resistor [0603]
R14
1 MΩ
1%
Resistor [0603]
T_EE10/11_TDK
1 mH
TDK flyback transformer
U1
VIPER17HN
Offline high voltage
converter
STMicroelectronics [DIP-7]
U2
TSM103W
Dual OP and voltage
reference
STMicroelectronics [SO-8]
T1
(1)
1. T1, the transformer design, is shown in Section 3.4 on page 11. Table 3 gives the basic electrical
characteristics, Figure 8 shows the winding structure, and Figure 9 illustrates the bobbin outline.
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3.3
General circuit description
PCB layout view
The PCB views are shown in Figure 6 and Figure 7.
Figure 6.
Top view
Figure 7.
Bottom view with SMD parts
!-V
3.4
!-V
Transformer design
Table 3.
Figure 8.
Basic electrical characteristics of flyback transformer (T1)
Name
Value
Core type
EE10/11-PC40
Bobbin type
BE10-118CPSFR
Primary inductance
1 mH +/- 10%
Leakage inductance
10 µH typical
Winding structure
!-V
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General circuit description
Figure 9.
AN2811
Bobbin outline
!-V
Table 4.
12/25
Bobbin dimensions
Dimension
Value
A
7.2 mm
B
3.5 mm
C
6.6 mm
E
3.85 mm
X
10.2 mm
Y
10.2 mm
Z
9 mm
P
0.5 mm
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4
Test results and waveforms
Test results and waveforms
Figure 10 shows the overall efficiency versus a range of AC line voltage loads with one LED
and two LEDs. Under both load conditions, we can observe that the efficiency drops when
input voltage increases. The maximum efficiency occurs at minimum AC line input
(176 VAC). Comparing a load condition of one LED with a load condition of two LEDs in
series, the efficiency increases by 7%. The efficiency with 1 LED is close to 75%.
Figure 10. Efficiency versus input voltage
!-V
Figure 11 shows us the standby power which is measured when the LED is disconnected.
Standby does not mean burst mode under light load. In standby, the overvoltage protection
works. Under various AC line inputs, the maximum standby power is 0.18 W at 264 V input.
Figure 11. Standby power versus input voltage
!-V
With the aid of the filter formed by C11, L2 and C3, no high-frequency interference can be
observed at the input current which definitely helps in meeting the conducted EMI standard.
In Figure 12 and Figure 13 the waveform is captured at 176 VAC. In Figure 14 and Figure 15
the waveform is captured at 264 VAC.
To choose the proper rating of the fuse, we always refer to the inrush current. There are two
inrush current plots at the AC line input 220 V: Figure 16 with one LED and Figure 17 with
two LEDs.
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Test results and waveforms
AN2811
Figure 12. Vin and Iin at 176 VAC, one LED
Figure 13. Vin and Iin at 176 VAC, two LEDs
!-V
!-V
Top trace: Vin (200 V/div)
Top trace: Vin (200 V/div)
Bottom trace: Iin (200 mA/div)
Bottom trace: Iin (200 mA/div)
Time: 4 ms/div
Time: 4 ms/div
Figure 14. Vin and Iin at 264 VAC, one LED
Figure 15. Vin and Iin at 264 VAC, two LEDs
!-V
!-V
Top trace: Vin (200 V/div)
Top trace: Vin (200 V/div)
Bottom trace: Iin (200 mA/div)
Bottom trace: Iin (200 mA/div)
Time: 4 ms/div
Time: 4 ms/div
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Test results and waveforms
Figure 16. Inrush current at LINE IN, one LED Figure 17. Inrush current at LINE IN, two LEDs
!-V
!-V
Iin: 5 A/div, 40 us/div
Iin: 5 A/div, 40 us/div
Max. value: 14.2 A
Max. value: 20.28 A
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Test results and waveforms
AN2811
The VIPer17 integrates one 800 V MOSFET and the drain current is limited at 0.6 A. The
drain-source voltage and drain current waveforms are shown in Figure 18 through 21. In
Figure 18 and Figure 19 the waveform is captured at 176 VAC. In Figure 20 and Figure 21
the waveform is captured at 264 VAC. The peak drain voltage, 496 V, is obtained at 264 V
load with two LEDs (see Figure 21). Under the same condition, the peak drain current is
384 mA.
Figure 18. Vds and Id at 176 VAC, one LED
Figure 19. Vds and Id at 176 VAC, two LEDs
!-V
!-V
Top trace: Vin (200 V/div)
Top trace: Vin (200 V/div)
Bottom trace: Iin (200 mA/div)
Bottom trace: Iin (200 mA/div)
Time: 4 us/div
Time: 4 us/div
Figure 20. Vds and Id at 264 VAC, one LED
Figure 21. Vds and Id at 264 VAC, two LEDs
!-V
!-V
Top trace: Vds (200 V/div)
Top trace: Vin (200 V/div)
Bottom trace: Id (200 mA/div)
Bottom trace: Iin (200 mA/div)
Time: 4 us/div
Time: 4 us/div
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Test results and waveforms
The current sense circuit (R9 and R12 in Figure 5) is one portion of output voltage. The
additional voltage drop is 300 mV. The following figures show the output voltage and current
waveforms for the load (one LED vs. two LEDs). In Figure 22 and Figure 23 the waveform is
captured at 176 VAC. In Figure 24 and Figure 25 the waveform is captured at 264 VAC. We
can observe that the output ripple current always less than 30 mA. Independent of the load
condition, the output current is regulated at precisely 500 mA.
Figure 22. Vo and Io at 176 VAC, one LED
Figure 23. Vo and Io at 176 VAC, two LEDs
!-V
!-V
Top trace: Io (200 mA/div)
Top trace: Io (200 mA/div)
Bottom trace: Vo (2 V/div)
Bottom trace: Vo (2 V/div)
Time: 2 ms/div
Time: 2 ms/div
Figure 24. Vo and Io at 264 VAC, one LED
Figure 25. Vo and Io at 264 VAC, two LEDs
!-V
!-V
Top trace: Io (200 mA/div)
Top trace: Io (200 mA/div)
Bottom trace: Vo (2 V/div)
Bottom trace: Vo (2 V/div)
Time: 2 ms/div
Time: 2 ms/div
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Test results and waveforms
AN2811
During the startup phase the output voltage response is optimized. No output voltage
overshoot nor voltage spike has occurred thanks to the soft-start function and optimum
regulation performance provided by the VIPer17. In Figure 26 and Figure 27 the waveform
is captured at 176 VAC. In Figure 28 and Figure 29 the waveform is captured at 264 VAC.
Figure 26. Startup of Vo and Io at 176 VAC, one Figure 27. Startup of Vo and Io at 176 VAC, two
LED
LEDs
!-V
!-V
Top trace: Io (200 mA/div)
Top trace: Io (200 mA/div)
Bottom trace: Vo (2 V/div)
Bottom trace: Vo (2 V/div)
Time: 10 ms/div
Time: 10 ms/div
Figure 28. Startup of Vo and Io at 264 VAC, one Figure 29. Startup of Vo and Io at 264 VAC, two
LED
LEDs
!-V
!-V
Top trace: Io (200 mA/div)
Top trace: Io (200 mA/div)
Bottom trace: Vo (2 V/div)
Bottom trace: Vo (2 V/div)
Time: 10 ms/div
Time: 10 ms/div
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Test results and waveforms
The load can be open-circuit (LED absent or wrong polarity at installation) or short-circuit
due to the system undergoing installation or an operating anomaly. The LED lamp can be
damaged due to overtemperature, for example. The system should be able to withstand
damage until removal of the anomaly, thanks to the VIPer17 which provides full protection
against output short-circuit as well as output open-circuit. In Figure 30 and Figure 31 the
waveform from the short-circuit load condition is captured at the highest AC line input 264 V,
which is the most hazardous condition to the system board. In Figure 32 and Figure 33 the
waveforms are captured at the highest AC line input 264 V with the output load in opencircuit condition.
Figure 30. Vdd and Vds at 264 VAC, output in
short-circuit
Figure 31. Io at 264 VAC, output in shortcircuit
!-V
!-V
Top trace: Vdd (10 V/div)
Io: 200 mA/div
Bottom trace: Vds (100 V/div)
Time: 100 ms/div
Time: 100 ms/div
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Test results and waveforms
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Figure 32. Vdd and Vds at 264 VAC, output in
open-circuit
Figure 33. Startup of Vdd and Vds at 264 VAC,
output in open-circuit
!-V
!-V
Top trace: Vdd (10 V/div)
Top trace: Vdd (10 V/div)
Bottom trace: Vds (100 V/div)
Bottom trace: Vds (100 V/div)
Time: 200 ms/div
Time: 10 ms/div
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Connection of AC line and LED lamp to the demonstration board
Connection of AC line and LED lamp to the
demonstration board
Figure 34. Completed demonstration board connection
!-V
Figure 35. Connection of AC line
Figure 36. Connection of LED lamp
!-V
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!-V
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Conclusion
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Conclusion
This document introduces a non-isolated offline constant-current LED driver based on the
VIPer17. The input range is 220 VAC +/- 20% and the device is capable of driving two
500 mA white light LEDs. The LED current is sensed and regulated through the TSM103W
and attains a constant output current. By using resistors with 1% precision, the output
current achieves a maximum tolerance less than 5%. The input fuse and input filter are built
on a 30 mm x 30 mm PCB. Overtemperature protection, LED open-circuit and LED shortcircuit protection are all integrated functions which enhance the reliability of the device.
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References
References
●
VIPer17, off-line high voltage converter (datasheet)
●
TSM103W, dual operational amplifier and voltage reference (datasheet)
●
STPS2H100A, power Schottky diode (datasheet)
●
STTH1R06A, turbo 2 ultrafast high voltage rectifier (datasheet)
●
BAT46JFILM, small signal Schottky diode (datasheet)
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Revision history
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Revision history
Table 5.
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Document revision history
Date
Revision
16-Jun-2009
1
Changes
Initial release
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