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PDF ( 数据手册 , 数据表 ) AL1678-20B

零件编号 AL1678-20B
描述 500V BUCK LED DRIVER
制造商 Diodes
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AL1678-20B 数据手册, 描述, 功能
AL1678-20B/10B/08B
UNIVERSAL, 500V BUCK LED DRIVER
Description
The AL1678-20B/10B/08B is a universal AC input (85 to 277 VAC),
high efficiency and high accuracy Buck LED driver. The AL1678-
20B/10B/08B topology provides accurate constant current over line
and load regulation with tight tolerance ±3%, operating at boundary
conduction mode (BCM) to ease in EMI/EMC qualification and testing
to meet the latest regulatory laws.
The AL1678-20B/10B/08B single Buck stage system works with a
single winding inductor and High voltage MOSFET included,
therefore, can use fewer external components and create a low bill of
material (BOM) cost solution. The AL1678-20B/10B/08B has rich
protection features to enhance the system safety and reliability. It has
thermal fold back function, which can reduce the output current when
the driver’s temperature is higher than the setting value.
The AL1678-20B/10B/08B is available in SO-7 package.
Features
> 90% Efficiency
Valley Switching to Achieve Low Switching Loss
Universal 85 to 277 VAC Input Range
Internal MOSFET up to 500V
Tight Current Sense Tolerance: ±3%
Low Start-up Current: 170µA
Low Operation Current: 100µA (Static)
Single Winding Inductor
Internal Protections
Under Voltage Lock Out (UVLO)
Leading-edge Blanking (LEB)
Output Open/Short Protection
Open-load and Reload Detection
Thermal Fold-back Function
Over Temperature Protection (OTP)
SO-7 Package
Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)
Halogen and Antimony Free. “Green” Device (Note 3)
Pin Assignments
(Top View)
OUT 1
VCC 2
ROVP 3
GND 4
7 Drain
6 LC
5 CS
SO-7
Applications
Retrofit LED Lamps
High Voltage DC-DC LED Driver
General Purpose Constant Current Source
Notes:
1. No purposely added lead. Fully EU Directive 2002/95/EC (RoHS) & 2011/65/EU (RoHS 2) compliant.
2. See http://www.diodes.com/quality/lead_free.html for more information about Diodes Incorporated’s definitions of Halogen- and Antimony-free, "Green"
and Lead-free.
3. Halogen- and Antimony-free "Green” products are defined as those which contain <900ppm bromine, <900ppm chlorine (<1500ppm total Br + Cl) and
<1000ppm antimony compounds.
Typical Applications Circuit
AC
Input
F1
DB1
C1
R1
D1
R4
C3
+
OUT
L1
R2
R3
C2
1 OUT Drain 7
2 VCC
3
ROVP
LC 6
4 GND CS 5
U1 AL1678-20B/10B/08B R5
AL1678-20B/10B/08B
Document number: DS37637 Rev. 1 - 2
1 of 13
www.diodes.com
April 2015
© Diodes Incorporated







AL1678-20B pdf, 数据表
AL1678-20B/10B/08B
Application Information (Cont.)
(
L1
2Vin _ rms Vo ) R5 Vo
VCS _ REF 2Vin _ rms f min
Where,
Vo is the output voltage.
Vin_rms is the RMS value of the input voltage.
According to the faraday’s law of induction, the winding number of the inductance can be got:
N L1
L1I peak
Ae Bm
L1VCS _ REF
Ae Bm R5
Where,
Ae is the core effective area.
Bm is the maximum magnetic flux density.
The AL1678-20B/10B/08B has designed the minimum tON time and maximum tON time, the tON_MIN is about 700ns and the tON_MAX time is about
35µs. In buck topology we can get the equation Vin_rms-VO = L*Ipeak/tON. If the inductance is very small, it leads to the tON becoming smaller, when
the system’s tON is smaller than tON_MIN, the device can’t detect the peak current of the system leading to wrong output current. While if the
inductance is very large, it leads to the tON becoming longer, when the system’s tON is longer than the tON_MAX, the system will trigger OVP, and
the LED will flicker. So the suitable value of the inductance is very important.
The AL1678-20B/10B/08B has also designed the minimum tOFF time and the maximum tOFF time, the tOFF_MIN time is about 6µs and tOFF_MAX time
is about 200µs. In buck topology we can get the equation VO = L*Ipeak/tOFF. If the inductance is very small, it leads to the tOFF becoming much
smaller, when the system’s tOFF is smaller than tOFF_MIN, the system will enter DCM mode, and the output current will be wrong. While if the
inductance is very large, it leads to the tOFF becoming much longer, when the system’s tOFF is longer than the tOFF_MAX, the system will enter CCM
mode, and the output current will also be wrong. So the suitable value of the inductance is very important.
Consider these parameters, two examples of the typical application inductance is recommended as below:
System Spec
60V/150mA (85 to 277VAC)
42V/100mA (85 to 277VAC)
Inductance Value
2.3mH
2.5mH
System Frequency
60KHz (230VAC)
62KHz (230VAC)
tON_MIN
2.5µs (265VAC)
1.7µs (265VAC)
tOFF
11.5µs
12.1µs
Fault Protection
Setting Output Open Voltage
The AL1678-20B/10B/08B has output open voltage protection, and the output voltage is controlled when the LED is open, which can prevent the
output voltage increasing to a very high value. This feature can help the system designer to select a smaller volume capacitor. The output voltage
is set by the external resistor R3 shown in Figure 1.
When the LED is open, the tOFF time can be calculated as
tOFF
L1VCS _ REF
VOVP R5
Where,
AL1678-20B/10B/08B
Document number: DS37637 Rev. 1 - 2
8 of 13
www.diodes.com
April 2015
© Diodes Incorporated














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