AL8812EV2 User Guide

AL8812EV2 User Guide
General Description
The MR16 LED Driver Module Evaluation
board shows how to use the new AL8812
with integrated MOSFET in one package as
a single stage Boost LED driver for an
inexpensive PFC front end for a cost
effective MR16 LED Driver circuit from
which high PFC (~0.9) can be achieved.
AL8812EV2 Specifications
Parameter
Value
Input Voltage
LED Current
Number of LEDs
12VAC
350mA (Adjustable)
26V LED Array
@350mA (Under
Tested)
1.06 ” x 0.71”
XY Dimension
Key Features





Integrated 60V, 3.6A MOSFET
Non-Dimmable or Triac Dimmable
Front end Constant On time PFC circuit
using the AL8812 Single Stage Boost LED
Driver
PFC for the 12VAC input allowing
multiple MR16 units on one
transformer
Compatible with Electronic
Transformers
Evaluation Board
AC-
LEDLED+
AC+
Figure 1: Top View
Applications



AC+
MR16 LED Bulb
Desktop lamps
Under the counter lamps
LEDAC-
LED+
Figure 2: Bottom View
Connection Instructions
Input Voltage: 12VAC (AC+, AC-)
LED Outputs: LED+ (Red), LED- (Black)
AL8812EV2 Rev1
August 2014
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Page 1 of 17
AL8812EV2 User Guide
Block Diagram:
12VAC
Input
PFC Boost
LED Driver
AL8812 with
integrated
MOSFET
Bridge
rectifier
LEDs
LED Current
Sensing
Feedback
AL8812EV2
Figure 3: Block Diagram
Evaluation Board Schematic
Figure 4: Evaluation Board Schematic
AL8812EV2 Rev1
August 2014
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AL8812EV2 User Guide
Evaluation Board Layout
Figure 5: PCB Board Layout Top View
Figure 6: PCB Board Layout Bottom View
AL8812EV2 Rev1
August 2014
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Page 3 of 17
AL8812EV2 User Guide
Quick Start Guide
1. By default, the evaluation board is preset at 350mA LED Current by R9.
2. Ensure that the AC source is switched OFF or disconnected.
3. Connect the 12VAC AC line wires of power supply to two test points of “12VAC” on the left
side of the board.
4. Connect the anode wire of external LED string to LED+ output test point.
5. Connect the cathode wire of external LED string to LED- output test point.
6. Turn on the main switch. LED string should light up.
Bill of Material
#
1
2
Name
3
4
5
6
7
8
9
10
11
12
13
D1-D5
IC1
IC2
Quantity
1
1
5
1
D6
1
D7
1
L1
1
R1
R2,R6,R7 3
1
R3,R4
1
R5
1
R8
1
R9
2
C1,C3
14 C2
1
15 C4,C5
16 C6,C7
17 C8
2
2
1
AL8812EV2 Rev1
August 2014
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Part number
AL8812
AS321KTR-G1
Manufacturer
Diodes Inc
Diodes Inc
Diodes Inc
Diodes Inc
BAV70-7-F
Diodes Inc
DDZ9717S
Wurth
7447714151
Panasonic
ERJ-2RKF4700X
Panasonic
ERJ-2RKF1001X
Panasonic
ERJ-2RKF10R0X
RCWE1210R240FKEA Vishay
Panasonic
ERJ-2RKF9091X
Panasonic
ERJ-3RQFR33V
C0402C102J5GACTU Kemet
SBR3U60P1
C1005X7R1H104K050
BB
C2012X5R1E106K125
AB
UKA1H330MDD1TD
CL21B105KBFNNNE
Description
Boost IC
Opamp
Super Barrier Rectifiers
BAV70 Dual diodes
Zener diode – 43 volts
150µH, 1.2A Inductor for PFC stage
470Ω Resistor 1/10W 1% 0402 SMD
1kΩ Resistor 1/10W 1% 0402 SMD
10Ω Resistor 1/10W 1% 0402 SMD
0.24Ω Resistor 1W 1% 1210 SMD
9.09kΩ Resistor 1/10W 1% 0402 SMD
0.33Ω Resistor 1/10W 1% 0603 SMD
1000pF Cer Cap 50V 5% 0402 SMD
TDK
100nF Cer Cap 50V 10% X7R 0402
TDK
Nichicon
Samsung
10µF Cer Cap 25V 10% X5R 0805
33µF Aluminum Cap 50V 20% Radial
1µF Cer Cap 50V 10% X7R 0805
Page 4 of 17
AL8812EV2 User Guide
Functional Performance (26V LED array @350mA peak)
AL8812EV2 Module Board Performance (without dimmer and electronic transformer)
Manuf
Diodes
Inc
Board Type
AL8812EV2
Module
Board
VIN
(VRMS)
12
IIN
(IRMS)
(mA)
777.3
PIN
(W)
PF
8.29
0.89
VLED
(V)
ILED
25.92
249.4
(IRMS)
(mA)
PLED
(W)
6.46
ILED
Ripple
(%)
8
Efficiency
(%)
77.95
Functional Waveforms
For 120VAC dimmable MR16 design bench testing:
The electronic transformer type is Hatch RS12-150 / 150W.
The dimmer type is Lutron SELV-300P.
Following is a block diagram of the bench circuit that indicates voltage and current designations
where the scope plots are functionally captured on the bench set-up. The bench set-up is used
in the evaluation of the AL8812EV2 module dimmable MR16 design.
Figure 7: Bench Set-up Circuit
AL8812EV2 Rev1
August 2014
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Page 5 of 17
AL8812EV2 User Guide
Waveform #1 (Maximum Dimming) => Channel 1: V1; Channel 2: I1
AL8812EV2 Board (Full Brightness)
Dimmer Voltage (V1)
Dimmer Current (I1)
Condition: IN=120VAC; OUT=26V LED Array / 350mA peak
Waveform #2 (Dimming Control ILED=350mA full brightness) => Channel 1: V1; Channel 2: I1
AL8812EV2 Board (Full Brightness)
ILED=350mA (Full Brightness)
Dimmer Voltage (V1)
Condition: IN=120VAC; OUT=26V LED Array / 350mA peak
AL8812EV2 Rev1
August 2014
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AL8812EV2 User Guide
Waveform #3 (Dimming Control ILED=250mA) => Channel 1: V1; Channel 2: I1
AL8812EV2 Board (ILED=250mA)
ILED=250mA
Dimmer Voltage (V1)
Condition: IN=120VAC; OUT=26V LED Array / 350mA peak
Waveform #4 (Dimming Control ILED=135mA Lowest Brightness) => Channel 1: V1; Channel 2: I1
AL8812EV2 Board (ILED=135mA Lowest Brightness)
ILED=135mA
Dimmer Voltage (V1)
Condition: IN=120VAC; OUT=26V LED Array / 350mA peak
AL8812EV2 Rev1
August 2014
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Page 7 of 17
AL8812EV2 User Guide
Waveform #5 (Maximum Dimming) => Channel 1: V2; Channel 2: I2
AL8812EV2 Board (Full Brightness)
Electronic Transformer Voltage (V2)
Electronic Transformer Current (I2)
Condition: IN=120VAC; OUT=26V LED Array / 350mA peak
Waveform #6 (Zoom-in for Maximum Dimming) => Channel 1: V2; Channel 2: I2
AL8812EV2 Board (Full Brightness)
Electronic Transformer Voltage (V2)
Electronic Transformer Current (I2)
3.24msec
Condition: IN=120VAC; OUT=26V LED Array / 350mA peak
AL8812EV2 Rev1
August 2014
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Page 8 of 17
AL8812EV2 User Guide
Waveform #8 (Dimming Control full brightness) => Channel 2: I2; Channel 3: I3
AL8812EV2 Board (ILED=350mA Full Brightness)
Electronic Transformer Current (I2) in 5A/DIV
ILED=350mA (Full Brightness)
Condition: IN=120VAC; OUT=26V LED Array / 350mA peak
Waveform #10 (Dimming Control ILED=250mA) => Channel 2: I2; Channel 3: I3
AL8812EV2 Board (ILED=250mA)
Electronic Transformer Current (I2) in 5A/DIV
ILED=250mA)
Condition: IN=120VAC; OUT=26V LED Array / 350mA peak
AL8812EV2 Rev1
August 2014
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Page 9 of 17
AL8812EV2 User Guide
Waveform #11 (Dimming Control ILED=26mA Lowest Brightness) => Channel 2: I2; Channel 3: I3
AL8812EV2 Board (ILED=135mA Lowest Brightness)
Electronic Transformer Current (I2) in 5A/DIV
ILED=135mA ( Lowest Brightness)
Condition: IN=120VAC; OUT=26V LED Array / 350mA peak
Waveform #12 (Maximum Dimming) => Channel 1: V2; Channel 2: I2; Channel 3: I3
AL8812EV2 Board (Full Brightness)
Electronic Transformer Voltage (V2)
Electronic Transformer Current (I2)
LED Output Current (I3)
Condition: IN=120VAC; OUT=26V LED Array / 350mA peak
AL8812EV2 Rev1
August 2014
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Page 10 of 17
AL8812EV2 User Guide
Waveform #13 (Maximum Dimming) => Channel 3: I3; Channel 1: V3
AL8812EV2 Board (Full Brightness)
LED Output Voltage (V3)
LED Output Current (I3)
Condition: IN=120VAC; OUT=26V LED Array / 350mA peak
AL8812EV2 Rev1
August 2014
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AL8812EV2 User Guide
Functional Data Curves
AL8812EV2 Rev1
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AL8812EV2 User Guide
Transformer Compatibility List
1) 120VAC to 12VAC Electronic Transformers without dimmers in 1 (26V) LED array:
Electronic Transformers
(120VAC to 12VAC)
Index
Brand
Model
1
RSA
RT60A (60W)
2
HATCH
RS12-150 (150W)
3
HATCH
RS12-60M-LED (60W)
4
HATCH
RS12-60M (60W)
5
HATCH
RS12-80M (80W)
6
HATCH
RS12-105 (105W)
7
HATCH
RS12-15M-LED (15W)
Performance Result
(No flicker)
√
√
√
√
√
√
√
2) 120VAC to 12VAC Electronic Transformers with dimmers in 1 (26V) LED array:
Electronic Transformers
(120VAC to 12VAC)
Index
Brand
Model
1
HATCH
RS12-60M-LED (60W)
2
HATCH
RS12-60M (60W)
3
HATCH
RS12-15M-LED (15W)
Note:
√ = No Flicker
AL8812EV2 Rev1
August 2014
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120VAC Dimmer Type
LUTRON
SELV-300P / 300W
LUTRON
MAELV-600 / 600W
√
√
√
√
√
√
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AL8812EV2 User Guide
Application Information
Circuit Description
This design consists of three sections:
1) The input boost circuit converts the 12VAC input voltage to a DC voltage around 26V
(AL8812).
2) The open circuit protection circuitry.
3) Finally, the LED current sense circuit generates a voltage to feedback the boost converter.
Boost Circuit
The AL8812 Boost converter is a simple “Constant ON time controller”. By keeping the same
ON time throughout the AC cycle, the circuit will draw a current that will closely match the
voltage and result in a constant input current. This eliminates the classic peak current problem
with a bridge rectifier and a large input filter capacitor.
The boost circuit includes the input bridge rectifier, EMI filter (if needed) and the AL8812 Boost
converter. The AC input voltage is rectified by the bridge circuit and filtered by C1, R4, C2, and
C5. This first filter removes the high frequency that is generated by the Electronic Transformer
in the range of 20-30 KHz. An additional diode rectifier circuit (D6, C4) is used to generate a
voltage that is used to power the circuit that will turn on/off the internal MOSFET of the Boost
converter and to power the operational amplifier in the LED current sense feedback circuitry.
The AL8812 has a current limit resistor R5 which sets the maximum current allowed through
the inductor L1. The output voltage is set to around 26 volts and filtered by the two capacitors
C6 and C7. These two capacitors store energy that will be used when the input voltage is low
during the AC cycle.
Open Circuit Protection:
This circuit is used to limit the output voltage from going above the voltage limit of the output
capacitors (C8) if the LED string is disconnected. In this example, a 35 volt output capacitor
would be a good choice so the output maximum voltage would be around 30 volts. The output
overvoltage is equal to the zener diode (D7) voltage plus the 1.2 volt threshold of the boost
feedback pin. Note be aware that zener diodes have a typical range of +/- 2 volts.
Overvoltage = 30v (zener voltage) + 1.2 v
Overvoltage protection range from 28 volts to 32 volts
AL8812EV2 Rev1
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Page 14 of 17
AL8812EV2 User Guide
LED Current sense circuit:
The current thru the LED is set with the LED sense resistor (R9). This control voltage is applied
to the feedback node of the boost converter. When the voltage on the feedback pin is over 1.2
volts, the boost converter will turn off. To keep the power dissipated in this resistor small, the
voltage is amplified by an amplifier with a gain of 10 reducing the resistance by 10.
The current in the LED string is:
Rsense (R9)
=
1.2 v
____________________
10 * LED Current (amps)
For a LED string current of 0.5 amps:
Rsense = 1.2 v / (10 * 0.5) = 0.25 ohms
(SMD 0603 resistor)
Setting the Boost Variables (AL8812)
The choice for the size of the boost converter inductor selected in this design is based on a
compromise which it is able to support a peak current to around 1.5A since the average input
voltage will be around 12-14V.
The boost converter (AL8812) includes a current limit resistor R5 which will limit the current
through the inductor and thus the power delivered to the output load. The formula for the
resistor is:
IPK(switch) = 0.25V / R5
For a current limit of 1A, R5 is 0.25Ω.
In this evaluation design, this value was selected based on having eight LEDs in series drawing
about 350mA. It was found that two 33µF capacitors mounted in parallel would just fit into the
cavity of the MR16 bulb.
Performance Description
The evaluation board allows the testing of different combinations of circuit component values
to match the final design specifications. The main design goal is to have a constant load on the
Electronic Transformer so that it will be operating throughout the AC cycle. This is accomplished
when the input power is about the same as the output power.
AL8812EV2 Rev1
August 2014
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Page 15 of 17
AL8812EV2 User Guide
Overall, there are three major components that are essential to the operation of the circuit.
The first component to select is the resistor (R9) in the LED current sense circuit that sets the
final current through the LED string. This will set the amount of power the system needs.
The second component is the value of the (R5) which limits the current provided to the output
filter capacitors. This should be adjusted so that the boost input circuit by AL8812 LED driver is
always running and thus providing a load to the Electronic Transformer. This usually means
that the output voltage of the boost circuit will have a large ripple. This will be okay as long as
the lowest voltage is higher than the maximum final LED string voltage.
The third component is the output capacitors (C6 and C7) of the boost circuit. These should not
be too large that the PFC circuit stops working. If it happens, the resonant circuit of the
Electronic Transformer will become erratic and cause the LEDs to flicker.
AL8812EV2 Rev1
August 2014
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Page 16 of 17
AL8812EV2 User Guide
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August 2014
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