RICHTEK(立錡)发光管选择指南 [ETC]
RICHTEK(立錡)发光管选择指南(2011.2).;
| 型号： | RICHTEK(立錡)发光管选择指南 |
| 厂家： | 
ETC |
| 描述： | RICHTEK(立錡)发光管选择指南(2011.2). |
| 文件： | 总8页 (文件大小：1067K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
February 2011
As the luminous efficiency of LED continues to grow, and the awareness of energy saving raises up within recent years,
the LED lighting applications are getting more and more popular. After successful delivery of LED backlight solutions,
Richtek launches a series of high power LED driver ICs for LED lighting. These products have been widely designed in
different applications, such as MR16, AR111, E27, T8, Par lamps, Light Bars, Ceiling lights, Street lights, and Car lights.
For DC input to constant current applications, Richtek introduces RT8450/2/3 and RT8480/2/8 series. These LED driver
ICs provide customers several different design options, including buck, boost, and buck-boost topology for different
loading currents. The current-mode constant current design which is different from the hysteretic solution, delivers
stable and precise LED current with small LC values. True current sense technology will maintain the current accuracy
regardless the change of input voltage, output voltage or inductance tolerance. This improves LED luminous consis-
tency and design flexibility. The ability of using multi-topology and wide input/output voltage range allow customers to
use the same IC or even same power boards for different applications.
RT8450 is typical out of this product line. With a built-in NPN power switch and being able to support Buck, Boost and
Buck-Boost modes, RT8450 is suitable for many types of applications. On the other hand, RT8482 is for high LED
current designs and is functionally compatible with RT8450 but has to be combined with an external MOSFET. These
two chips can cover most of the single string LED lighting applications. RT8452 is another good product which can
provide sharp PWM dimming support and operate with high speed PWM dimming signal up to 50KHz, and it is a good
fit for high resolution LED projector applications.
RT8470 and RT8471 provide very low cost MR16 solutions with high electronic transformer compatibility. A simple
circuit design can eliminate most of the flickers and provide very high efficiency.
For AC input to constant current applications, Richtek offers RT8454/6/7 secondary-side constant current controllers to
generate highly accurate current over wide input/output voltage range and also wide temperature range without suffer-
ing from the transformer accuracy. RT8456 can work with many different primary side topologies to improve the output
current accuracy. This will unify the luminance of E27 LED light bulbs when a lot of them line up together. RT8454/7
support different kinds of dimming functions including Triac Dimming. The secondary side modulation provides a more
precise current control than the primary side dimming scheme. The secondary-side dimming chip, RT8457, is used
widely not only for Triac dimming but also many of other dimming technologies.
The multi-channel designs of RT8454 allow a single chip to provide well-balanced constant current to up to 6 strings of
LED. This will benefit the high power applications such as street lights to save cost. RT8454 also provide interfaces to
link multi-chip together. This design makes single primary side can control up to hundreds of LED strings.
As the understanding of LED lighting regulation is improved, the non-isolated design starts to be popular. A good isola-
tion design on mechanical makes the non-isolated design on power module become possible. This will bring the system
higher efficiency and lower cost and these are two key points to decide whether a product can be successful or not.
RT8458 is announced to introduce a high efficiency and low cost PAR lights or T5, T8 solution. A special floating-buck
topology improves the efficiency and also provides very simple methods of OVP and OCP. The true current sense
technology keeps precision current over universal input range. RT8459 is a PFC version of RT8458. With proper output,
designing PAR lights or T8 with RT8458 and RT8459 can keep efficiency > 90% and PF>0.9 easily. (PS: RT8459 is
expected to be announced on March 2011.)
High efficiency, low cost PAR lights, T8
design with RT8458 and RT8459
innovative self-biasing design that reduces power loss
and eliminates the need for any complex external
transformers or start-up circuitry in non-isolated applica-
tions. Instead, these devices require only a few simple
low-cost components. An integrated high-side floating
gate driver controls an external MOSFET that may be
selected to support all popular AC line voltages. The
programmable LED DC current is regulated by a precise
averaging current feedback loop that keeps LED current
constant over large line voltage variations, and will
compensate for poorly controlled system component
tolerances. The RT8458/9 integrate protection for fault
conditions, including open and shorted LED strings,
Under Voltage Lockout (UVLO), Over Current Protection
circuit (OCP) and Over Voltage Protection (OVP).
factor (PF) compensatio
circuitry to optimize AC
utilization.
Features-RT8458, RT8
■
Low Cost and Efficient Buck Converter Solution
■
Universal Input Voltage Range with Off-Line Topology
■
Programmable Constant LED Current
■
Dimmable LED Current by ACTL
■
Output LED String Open Protection
■
Output LED String Short Protection
■
Output LED String Over Current Protection
■
Built-in Thermal Protection
■
Built-in High Power Factor Correction Circuit (RT8459)
RT8458 efficiency measurement
Eff. vs. LED pcs (350mA)
100%
95%
90%
85%
80%
110VAC
75%
220VAC
70%
3
4
5
6
7
8
9
10
LED pcs
With the RT8458 you get precise,
constant LED current
An eꢀciency >90%, PF>0.9 PAR light design with RT8459
8459 Vout=44V//200mA/15LEDs
Vin.ac (V)
90
Vo (V)
43.33
43.37
43.35
43.31
43.36
43.41
Io (mA)
194
Pin (W)
9.3
Po (W)
8.41
8.50
8.45
8.27
8.41
8.51
PF
Eꢀ. (%)
90.39
91.80
91.98
91.61
91.14
90.32
current oꢀset (%)
-1.02%
0.980
0.981
0.985
0.972
0.955
0.932
110
196
9.26
9.19
9.03
9.23
9.42
0.00%
130
195
-0.51%
180
191
-2.55%
220
194
-1.02%
264
196
0.00%
RT8456, RT8457 Secondary Side
Constant Current LED Driver and
Dimming Controller
The RT8456 is an isolated secondary LED current
controller designed specifically for lighting fixtures such
as E27, GU10, T5 and T8. The IC is suitable for applica-
tions that require power line isolation for safety and
reliability, high conversion efficiency, as well as high LED
current accuracy.
and an opto-coupler driver to control the primary side of
the transformer to complete the system loop.
RT8457 provides dimming function on secondary side.
Precise dimming is achieved by controlling the LED
current at the secondary side via analog dimming.
Applying a voltage greater than 1.1V at the ACTL pin will
set the LED current sense threshold between the LED
and GND pins at the highest level. The maximum LED
current is programmed by the sense resistor between
the LED and GND pins. Lowering th
will reduce the LED current sense th
The RT8456 contains 1) a constant current regulating
amplifier with 60mV threshold used to program the LED
string current with a simple resistor to within 5% LED
current accuracy; 2) an over voltage comparator to
protect the output when LED string is open or broken; 3)
Features-RT8456
ures-RT8457
■
Secondary Side LED Curre
condary Side LED Current Reg
■
4.75V to 48V Operation Ra
gh Accuracy 58.5mV LED Curr
■
High Accuracy 60mV LED C
reshold Control
Threshold Control
5mA Operating Current
■
0.6mA Operating Current
ogrammable LED Current
■
Programmable LED Curren
ecision Secondary Side LED C
■
Output Over Voltage Protec
ecision Analog Dimming at Sec
■
Small SOT-23-6 Package
utput Over Voltage Protection
OP-8 Package
RT8456 application circuit
RT8457: Linear LED current mapping between LED
current and ACTL voltage
VOUT
Opto
ILED vs. VACTL
350
Vcc
300
RT8456
LED String
2.5V
OUT
OVP
250
200
150
100
50
CV
Primary
side
-
+
60mV
CC
-
ILED
+
0
CP
CN
GND
0
0.2
0.4
0.6
0.8
1
1.2
1.4
V
ACTL(V)
Rs
GND
RT8457 application circuit
VOUT
Opto
C1
Primary
side
1
R1
R
LED
VCC
2
2V2
3
OUT
C2
Optional
C
IC2
R
IC2
LED String
RT8457
5
6
4
7
GND
OVP
LED
C
IC1
R2
R
IC1
ACTL
RT8456 and RT8457 work with most of the primary side topologies
to provide constant current LED driver and dimming function.
R
S
Typical DC to CC LED driver design with
RT8450/RT8482
V
IN
The RT8450 is a current mode constant current LED
driver with 1.5A switching MOS inside, supporting
multi-topology includes buck, boost, and buck-boost. It
provides very wide input and output range. Input voltage
works from 4.5V to 40V, and this can be extended by
zener diode added. Output voltage can be up to 50V.
RT8482 is an external MOS version of RT8450 to
support higher power applications. A higher voltage
product – RT8462 is ready soon.
4.5V to 40V
C1
RT8450/B
R2
190mV
ISP
ISN
VCCx
R3
R4
PWM
ACTL
DCTL
Dimming control
OVP
GND
EN
VC
SS
C4
5V
R1
L
■
High Voltage : VIN Up to 40V, VOUT Up to 50V
10k
20µH
SW
■
Buck, Boost or Buck-Boost Operation
Easy Dimming : Analog, PWM Digital or PWM
C3
10nF
C2
3nF
■
Converting to Analog with One External Capacitor
■
Programmable Soft Start to Avoid Inrush Current
■
Programmable Over Voltage Protection to Limit
RT8450 buck
■
Output Voltage
■
VIN Under Voltage Lockout and Thermal Shutdown
RoHS Compliant and Halogen Free
L
■
20uH
V
IN
4.5V to 40V
C1
C5
1µF
The average current sense constant current controller,
different from peak sense, provide a stable and high
precise LED current. Regardless of the input voltage
change or LED number change, the variation of LED
current is very small. It is very easy to design a general
purpose LED power module with RT8450 or RT8482 for
flexible input and output.
RT8450/B
SW
ISP
ISN
VCCx
EN
R2
190mV
5V
DCTL
PWM
Dimming control
VC
R3
R1
10k
SS
V
OUT
OVP
GND
VISP – VISN Threshold vs. Input Voltage
ACTL
C3
10nF
R4
196
194
192
190
188
186
C2
3nF
C4
0.5µF
RT8450 boost
C5
L
V
IN
V
OUT
4.5V to 40V
20uH
4
13
22
31
40
C1
Input Voltage(V)
RT8450/B
SW
VCCx
EN
LED Current vs. ACTL
5V
ISP
ISN
2500
2000
1500
1000
500
R2
DCTL
PWM
Dimming control
190mV
VC
R3
R1
V
OUT
OVP
GND
SS
10k
ACTL
R4
C3
10nF
C2
3nF
C4
0.5µF
0
RT8450 buck-boost
0.2
0.4
0.6
0.8
1
1.2
1.4
ACTL(volt)
Design challenges for
MR-16 retrofit LED drivers.
lighting applications are being replaced by
rectified and smoothed by the bulk c
LED’s. One of these “retrofit” applications is appears that the rectified voltage sh
the low voltage halogen lamp, generally
called “MR-16” after its low voltage lamp
connector.
sufficient to use a standard BUCK
converter to drive the LED string.
In practice, it’s a bit different: Most h
Low voltage halogen lamps generally range ET’s use a self-oscillating half-bridge
from 20 ~ 50 Watts, and are powered from
12Vac. In many cases, an “Electronic
Transformer” (ET) is used to efficiently
convert the mains AC voltage to 12Vac. ET
output power ranges from 50 ~ 150W, so
it’s possible to connect several halogen
converter with proportional base driv
which modulates the mains sine wav
a 30 ~ 50khz switching waveform.
Designed to drive 20~50W resistive
ET’s need a certain minimum load fo
continuous switching throughout the
in very short conduction time of the ET,
increasing peak inrush current and
lamps in parallel to one ET. With some ET’s cycle. A standard BUCK LED driver
it is even possible to use phase-cut
dimmers to regulate the light output.
poses two problems:
●
The input bridge and bulk cap are
Replacing a standard halogen lamp with a
LED light is not as straightforward as one
would think. When trying to design a LED
driver that works with the ET 12Vac output,
it quickly becomes clear that there are
several compatibility issues that can be
quite tricky to solve. This article describes
some background and possible solutions.
resistive
●
LED’s are more efficient than halogen
making the ET’s more prone to instability.
lamps so they consume much less power
than the ET minimum load.
2.Use a small bulk capacitance to increase
the input ripple for the LED driver. A high
performance BUCK converter like the
RT8453B or RT8470 (see figure 1), can
smoothly drop out when the input voltage
is lower than LED string voltage, resulting
in some 120Hz ripple in the LED current
As long as this 120Hz ripple is steady, the
flicker will not be noticeable to the human
eye.
As a result ET switching can become
erratic over the mains cycle. Depending on
the ET type and the LED driver
configuration, LED flicker can result.
The block diagram below shows an
example of an LED light connected to a
Several solutions can improve the
compatibility between ET’s and a LED light.
LED lamp
3.To obtain a more stable LED current
even with a large input ripple, use a
buck-boost configuration (i.e. by using
RT8450 in buck-boost mode). This will
provide a more stable LED current with
minor 120Hz ripple. A drawback is the
inherently lower efficiency of a
LED driver
LED string
~
+
Electronic
Transformer
Cin
AC mains
~
Power ~ 4.5W
Designed for 20 - 50W
sistive load
Re
Constant current driver
Bridge rectifier with bulk capacitor
buck-boost topology.
4.When using a dimmable ET with
compatible dimmers, the ET output
voltage will be phase cut, depending on
the dimmer setting. However, since most
ET’s will not switch continuously over the
full mains range, accurate phase cut
detection is problematic. Adopting a
circuit that detects the average voltage of
the rectified ac, and reduces LED current
when the input voltage is reduced can
improve dimming performance. See
figure 2 for an example..
Detailed schematics
Figure 1 RT8453B MR-16 standard application
C4
1u
R2
0.5R
D2
SR26
R3
100k
C3
220u/25V
D3
SR26
Vcc
+
ISN
12Vac from
Electronic
Transformer
R1
0.5R
D1
SR26
EN
C5
RT8453BGSP
D6
SR26
D4
SR26
4.7u
ACTL
L1
22uH
VC
SS
SW
R5
10k
C6
3n3
GND
C7
10n
Designing LED drivers for an MR-16 retrofit
application is possible, although halogen
Electronic Transformers and LED driver
circuits are hardly made for each other. By
using some circuit tricks and correctly
choosing an LED driver IC, a relatively
simple and low cost solution can be
designed that works with most ET’s. For
more information about Richtek’s broad line
of LED driver solutions, visit
Figure 2 RT8453B MR-16 dimmable application
C4
1u
+
R2
0.5R
D2
SR26
C3
100u
Z1
18V
R6
100k
C1
10u
Vcc
12Vac from
ISN
EN
Electronic
Transformer
R1
0.68R
R3
180k
C5
RT8453BGSP
D6
SR26
D1
SR26
C2
10u
4.7u
ACTL
C8
10u
R4
27k
L1
22uH
VC
SS
SW
www.richtek.com/LED/
R5
10k
GND
C6
3n3
C7
10n
High Efficiency Universal LED
Driver Solution for Emergency Lights
with RT8482
by adjusting ACTL voltage with a potenti- for the lighting area. This 3P2T switch
ometer for varieties of LED current
ratings.
iver. The LED’s can be connected
s with 5~12 pieces per string, with
al LED voltage of 16V to 48V.
se the battery pack voltage can be
r higher than the LED voltage,
oost topology will be used for
of the combinations of supply
e range and a number of LED’s.
ses of LED voltage always higher
upply voltage will use boost
gy because of the better efficiency
wer component voltage rating
red to buck-boost topology.
physically changes all three contact
points as shown above simultaneously.
Introduction
A universal high efficiency LED emer-
gency light application diagram using
RT8482 with three configurable switches mode should be used when input supply
is shown below. It’s recommended to use voltage is lower than the total LED
a 3-in-1 interlocked switch (also known
as 3P2T switch) for mode-selection.
Buck-boost mode should be used when
input supply voltage is higher or lower
than the total LED forward voltage. Boost
forward voltage.
Although buck-boost mode itself can
cover all application corners, the
efficiency for boost mode is higher than
buck-boost’s efficiency, due to the
effective power to the LED in boost mode
is higher than that of buck-boost mode.
Evaluation Board (EVB) Description
RT8482 EVB provides a convenient
mode configuration for LED emergency
lighting application accepting wide range
of input voltages and flexible number of
LED to the light fixtures. A buck-boost or
boost mode can be easily configured by
This application note provides a simple
universal circuit that can be easily
configured in the field with optimum
efficiency and minimum required compo-
nent rating for LED emergency lights.
For example in a 5-LED design with 18V
voltage input in buck-boost mode, the
LED sees the effective 16.5V (5*3.5V) ,
but the total switch node voltage equals
34.5V (18V+16.5V) with respect to
ground. It’s the same VIN, VOUT
condition as an 18V to 34.5V boost mode
conversion. They have similar conversion
losses and the buck-boost delivers less
output power than the corresponding
boost, which explains the efficiency
difference between the buck-boost and
the boost.
Vin
S1, S2, S3:
=boost
Cin
30uF
15
L1
=buck-boost
RT8482
VCC
EN
S1
D1
Vout
13
1
5V
R30
Q1
Cout
4.7uF
GBIAS
2
GATE
ISW
LED's
27k
C2
0.47uF
4
Rsw
0.05
9
S2
ACTL
DCTL
R29
5.0k
R31
Another benefit of boost design over
buck-boost is the lower requirement in
component voltage rating, especially for
the MOSFET Q1 and Schottky diode D1.
VOUT of boost is roughly the total
forward voltage of the LED string, while
VOUT of buck-boost is the total forward
voltage of the LED string plus VIN.
Higher VOUT requires higher component
rating of Q1 and D1.
6
7
10
Analog
Dimming
ISP
0.2V ~ 1.2V
S3
Rsense
ISN
680
8
VC
SS
R32
390k
R14
14
OVP
R21
Vout
169k
R2
10k
C11
10n
11
C5
3.3nF
10k
Css
10nF
GND
16, Exposed Pad (17)
NC 3 5 12
RT8482 EVB runs in high efficiency. All
the components of this design generate
very little heat, thus enhance the reliabil-
ity and safety of the lighting fixture. This
design for universal applications
minimizes the inventory and manage-
ment effort for both manufacturer and
installer.
Efficiency Performance
LED Qty
V(LED)
5
6
7
8
9
10
11
12
16~20V 22~28V 25~32V 25~32V 28~36V 32~40V 35~44V 38~48V
VIN 24V
Bk-Bst Bk-Bst Bk-Bst Bk-Bst
Boost
Boost
Boost
Boost
(20~28V)
(84%)
(86%)
(87%)
(87%)
(93%)
(93%)
(93%)
(93%)
VIN 18V
Bk-Bst
Boost
Boost
Boost
Boost
Boost
Boost
Boost
(15~21V)
(86%)
(93%)
(93%)
(93%)
(93%)
(93%)
(93%)
(93%)
Evaluation Board Picture & Illustration
VIN 12V
Boost
Boost
Boost
Boost
Boost
Boost
Boost
Boost
(10~14V)
(91%)
(92%)
(92%)
(92%)
(92%)
(92%)
(92%)
(92%)
VIN Terminal
GND Terminal
Potentiometer
Case Temperature on Major Components
VIN=12VDC, 5 LED, boost mode, ambient temperature ﹫25°C
LED Anode
Terminal
RT8482
RT8482
Inductor
MOSFET
Schottky diode
Rsense
Output capacitor
36.0
33.8
32.5
35.6
31.2
26.1
VIN =24VDC, 5 LED, buck-boost mode, ambient temperature ﹫25°C
3P2T
Switch
RT8482
Inductor
MOSFET
Schottky diode
Rsense
Output capacitor
46.1
42.4
38.5
41.5
34.5
36.9
LED Cathode Terminal
LED Lighting Selection Guide Sorted by Application
Application
Feature
Richtek Solution
Solid-State Lighting AC or DC Input
MR16, AR111
Buck, Buck-Boost, Boost
Flyback, non-isolated
Flyback, non-isolated
Boost, Flyback, non-isolated
Boost
RT8450B, RT8482, RT8453, RT8470, RT8471
RT8456, RT8457, RT8458, RT8459
RT8456, RT8457, RT8458, RT8459
RT8450B, RT8482, RT8456, RT8458, RT8459
RT8450B, RT8482, RT8480
GU10, E27,PAR30,PAR38
T5, T8 Light Bar
Oꢀce Lamp
Decoration Light
Street Light, Solar Light
Emergency Light
RGB Light
Buck, Boost, ꢁyback
Boost
RT8480, RT8482, RT8488, RT8470
RT8450B, RT8482
Buck
RT8453, RT8470
Freeze Light
Buck, Flyback, non-isolated
Synchronous Buck
RT8450B, RT8453, RT8456, RT8470, RT8458
RT8452
Projector
Automotive Application
Interior Light
Buck, SEPIC, Buck-Boost
Buck, SEPIC, Buck-Boost
Buck, SEPIC, Buck-Boost
RT8450B, RT8482, RT8488, RT8480
RT8450B, RT8482, RT8488, RT8480
RT8450B, RT8482, RT8488, RT8480
Exterior Light
Automotive Light
About Richtek
Richtek Technology Corporation is one of the world’s leading analog IC companies. The company consis-
tently delivers inventive power management solutions that improve the performance of consumer electron-
ics, computers, and communications equipment. Richtek adds value to end equipment by synthesizing
technological innovation, uncompromised quality, and devotion to customer service. Founded in 1998, the
Company is headquartered in Taiwan with additional offices in Asia, the U.S., and Europe. Richtek is
publicly traded on the Taiwan Stock Exchange under the ticker symbol 6286. For more information about
Richtek and its analog IC solutions, please visit the Company’s Web site at www.richtek.com or
www.richtek.com/LED.
US Office
Europe Office
Taipei Office
led@richtek.com
Tel: 1-408-9690226
Tel: 31-40-8515520
Tel: 886-2-86672399
www.richtek.com/LED/
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