AL1676 Datasheet, PDF (8/15 Pages) Diodes Incorporated – UNIVERSAL HIGH POWER FACTOR BUCK LED DRIVER

AL1676
Functional Description and Application Information
Convertor Operation
The AL1676 is a high efficiency and high power factor BUCK LED driver solution for universal input application based on single winding inductor. It
is available for 6 internal MOSFET options (300V/2A, 300V/3A, 500/1A, 500V/2A, 600V/2A, 650V/4A) which can help to reduce the overall LED
driver solution size of the LED lamp. This 6 MOSFET options can cover most of the 3~18W applications.
High power factor (PF) is achieved by constant on-time control. Coupled with simple closed loop of constant current control, the AL1676 can
achieve good line and load regulation. The AL1676 adopts source-driver technique to decrease the system operating current. It uses a novel
method to detect the tOFF time which helps to get rid of an auxiliary winding for (VCC supply and) detecting the tOFF time, resulting in an extremely
low bill material (BOM). The AL1676 operates at boundary conduction mode (BCM) which can ease EMI design.
AC
Input
L1
F1
DB1
C1
C2
R1
R2
VR
C3 _{R3 C4}
U1 AL1676
VCC
D
ROVP
COMP NC
GND CS
D1
R4
C5
+
L2
R5
OUT
Figure 1. Typical Application Circuit
Start-up and Supply Voltage
Before start-up, the VCC capacitor C3 is charged by the startup resistors (R1, R2) from the high voltage mains. When the start-up voltage is
reached, the AL1676 starts switching. During normal operation, the VCC supply is provided by start-up resisters (R1, R2) and internal source
driver circuit.
The AL1676 has an internal VCC clamp voltage (typical 15.5V), which is limited by one internal active Zener diode.
When VCC voltage drops to below the under voltage lockout (UVLO), switching stops, the IC can restart when the voltage on VCC pin is
exceeding the startup voltage (VTH(ST)).
Protections
Under Voltage Lockout (UVLO)
When the voltage on the VCC pin drops to below VOPR(Min), the IC stops switching. The IC can restart when the voltage on VCC exceeds the
startup voltage (VTH(ST))
Leading-Edge Blanking (LEB)
To prevent false detection of the peak current of the inductor, a blanking time following switch-on is designed. When the internal switch turns on, a
short current spike can occur because of the capacitive discharge of the voltage over the drain and source. It is disregarded during the LEB time
(tON_MIN).
Cycle-by-cycle Over Current Protection (OCP)
The AL1676 has a built-in peak current detector. It triggers when the voltage on CS pin reaches the peak level VCS_CLAMP. The R5 is connected to
the CS pin to sense the current of the inductor. The maximum peak current (IPEAK(MAX)) of the inductor can be calculated as below:
I _{PEAK MAX }
 ^{VCS _ CLAMP}
R5
…………… ⁽¹⁾
AL1676
Document number: DS38290 Rev. 1 - 2
8 of 15
www.diodes.com
February 2016
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