1.1A Buck for one to three LEDs in series (AL8806EV6)

AL8806EV6 USER GUIDE
Performance
Introduction
•
•
•
•
This evaluation circuit demonstrates the
AL8806 High Efficiency 30V 1.5A Buck LED
Driver operating in a circuit providing 1.1A
LED current in MR16 form intended to drive 1
to 3 high brightness LEDs in series with a total
load voltage drop up to 10V. The circuit
includes a 470µF reservoir capacitor to
prevent flicker for 50Hz or 60Hz AC input
power. EMC filtering is included to meet
international standards including the radiated
emission requirements of EN55015 and
EN55022 Class B.
•
12VDC and 12VAC input
1.1A LED current
Drives 1 to 3 LEDs in series
2% current regulation 9V to 30VDC
(with 2 LEDs)
Ambient temperature range
-40°C to +105°C
Ordering Information
Order Number
AL8806EV6
The switching frequency is approximately
440kHz when driving 2 Osram Dragon
Diamond LEDs.
The construction uses a double-sided FR4
printed circuit board, 17 x 20 x 0.8 mm with
2oz/sq ft copper (70µm). Components are
mounted on both sides.
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AL8806EV6
Quick Start Guide
Suitable Test Equipment
Count
Description
1
Adjustable Power Supply, 12V
2A
2
Digital Multimeter
1
Digital Storage Oscilloscope
2
LED, high brightness, “Dragon
Diamond”, series connected on
suitable heat conducting PCB
Manufacturer
Part Number
Thurlby Thandar
CPX400A
Fluke
179
Tektronix
TDS2024B
Osram
CAUTION: The LEDs are very bright. Ensure
they are hidden from direct view, or covered
with a dispersing filter. The lid from an
aerosol can is convenient for this.
Also the LEDs are very hot. Do not touch!!
Lamp Operation
1. Set the power supply to 12.0V but do not switch on. Set the current limit to 2.0A.
2. Connect up the AL8806EV6 board to the equipment as in Figure 1 below. Set DMM1 and
DMM2 to measure current up to 2A.
Figure 1: Test Schematic using VDC Input
3. Cover the LEDs to avoid dazzling.
4. Switch on the power supply. This should illuminate the LEDs. Note that the input current
(DMM1) is approximately 690mA. The output current (DMM2) is approximately 1.12A. The
input voltage can be varied from approximately 9VDC to 30VDC and the current regulation
observed is typically within ±2%.
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AL8806EV6
Observe Switching Waveform
5. The switching waveform can be observed on an oscilloscope.
6. Set the oscilloscope as follows:
Channel 1 sensitivity:
Time base:
Trigger Source:
Trigger Mode:
2V/div (at probe tip)
1µs/div
CH1
Auto
7. Connect the ground lead of a 10x probe to the supply negative terminal near P2 of the
AL8006EV2, and touch the probe tip onto the anode of D1 as in Figure 2 below. On the
oscilloscope, press RUN/STOP to capture the waveform. The cursor readout indicates a
switching frequency of 440kHz approximately.
Figure 2:
Figure 3: Oscilloscope Waveform
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AL8806EV6
AL8806EV6 Schematic
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AL8806EV6
PCB Copper Layout & Silk Screen – Top
PCB Copper Layout & Silk Screen –Bottom
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AL8806EV6
Parts List
Count
Designator
Description
Package
1
C1
Capacitor, 470uF, 25V
Aluminium Electrolytic
Radial,
10 x 12.5mm
Manufacturer
Part Number
Rubycon
25ZLH470M
1
C2
Capacitor, 4.7µF 10%
50V X7R
1210
Kemet
C1210X475K5RAC
3
C3 C9 C10
Capacitor, 100nF 10%
50V X7R
0805
Kemet
NIC
NMC0805X7R104K50TRPF
1
C4
Capacitor, 100nF 10%
50V X7R
1206
Kemet
NIC
NMC1206X7R104K50TRPF
4
C5 - C8
Capacitor, 1.5nF 10%
50V or 100V, COG
0805
generic
1
L1
Inductor, shielded,
15µH 20%
6.6 x 6.6mm
Coilcraft
NIC
Würth
MSS7341-153ML
NPIS64D150MTRF
744777115
1
L2
Inductor, ferrite bead,
6A, 30ohms @100MHz
0805
TDK
MPZ2012S300A
1
R1
Resistor, 0.15ohms 1%
250ppm 125mW
0805
generic
1
R2
0805
generic
1
D1
4
D2 - D5
1
U1
Resistor, 0.2ohms 1%
250ppm 125mW
Diode, schottky, 30V
2A DFLS230
(alternatives:
DFLS230L or LH)
Diode, Super Barrier
Rectifier, 30V 2A
SBR2U30
IC, LED Driver, AL8806
C1210X475K5RAC
C1206104K5RAC7800
PowerDi123
Diodes Inc
DFLS230-7
PowerDi123
Diodes Inc
SBR2U30P1-7
MSOP-8EP
Diodes Inc
AL8806MP8-13
I/O
Count
Designator
Description
Function
1
Manufacturer
P1
Solder pad
VDC, VAC Input
1
P2
Solder pad
VDC, VAC Input
1
A
Solder pad
LED Anode load
1
K
Solder pad
LED Cathode load
Part Number
Recommended Operating Conditions
Symbol
Parameter
Min
Max
Units
VDC
Input Supply Voltage, VDC
8
30
V
VAC
Input Supply Voltage, VAC
8
20
Vrms
VOUT
Load voltage ( 1 to 3 LEDs)
0
10
V
TA
Operating Ambient
Temperature
-40
+105
°C
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AL8806EV6
Current Setting
The LED current is set by the sense resistor value, RSENSE. On this PCB, there are two resistors in
parallel.
RSENSE = R1 * R2 / (R1 + R2)
For the schematic values this gives a resistance of 0.15 * 0.2 (0.15 + 0.2) = 0.0857 ohms.
The LED current flows through RSENSE. The sense voltage is 100mV, so the LED current is simply
ILED = 0.1/ RSENSE
For the schematic values this gives an LED current of 0.1/0.0857 = 1.167 A nominally. In practice
there is a slight reduction in current partly due to the resistance of the PCB copper, depending on the
PCB layout. At 1.1A this reduction is typically about 5% using AL8806EV6.
The following table gives commercially available resistor values for typical current requirements,
allowing a current error of 3% maximum not including the effect of PCB copper. A power limit of
125mW is assumed for the 0805 size resistors with 50% de-rating.
LED Current
150mA
300mA
380mA
500mA
660mA
1A
1.1A
R1, ohms
0.68
0.33
0.51
0.2
0.15
0.2
0.15
R2, ohms
DO NOT FIT
DO NOT FIT
DO NOT FIT
DO NOT FIT
DO NOT FIT
0.2
0.2
Performance
The performance of the AL8806EV6 demonstrated shows the capability to regulate LED current. The
LED current of 1.1A is approximately 5% lower than the calculated value. This is partly due to copper
resistance. With a load of 2 LEDs, the current changes by less than ±2% over the input voltage range
from 9VDC to 30VDC. With 2 LEDs and a supply of 12VDC, the switching frequency is approximately
440kHz.
For further advice, please contact your local Diodes Field Applications Engineer, or one of our
sales offices listed on the back page of this document.
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AL8806EV6
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