AL1788
Document number: DS39401 Rev. 1 - 2
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AL1788
NEW PROD UCT
LOW STANDBY POWER PFC CONTROLLER
Description
The AL1788 is a high performance AC/DC Power Factor Correction
(PFC) controller targeting at LED lighting applications. Based on
Primary Side Regulation (PSR) implementation, AL1788 does not
require opto-coupler and any secondary feedback circuit to save overall
BOM cost. It operates at Quasi-Resonant (QR) mode where MOSFET
is turned on at the valley of the drain voltage, which minimizes switching
loss to result in high efficiency.
With either Flyback or Buck topology, AL1788 system supports high
efficiency, high Power Factor (PF>0.9) and low Total Harmonic
Distortion (THD <20%) for universal input at wide loading range (50%
loading to 100% loading)
The AL1788 features low start-up current, low operation current and low
standby power. It has rich protection features including Over Voltage
Protection (OVP), Short Circuit Protection (SCP), Over Current
Protection (OCP) and Over Temperature Protection (OTP).
The AL1788 is available in SOT26 (SC74R) package for the controller.
Features
PSR Implementation Based on Flyback and Buck Topology
Universal AC Voltage Input for Constant Voltage (CV) Regulation
Valley Detection for Primary MOSFET Switch to Achieve Low
Switching Loss and High Efficiency
High PF (>0.9) and Low THD (<20%) for Wide Loading Range
(50% to Full Loading)
Internal Protections:
Under Voltage Lockout (UVLO)
Over Voltage Protection (OVP)
Over Current Protection (OCP)
Output Short Protection (OSP)
Over-Temperature Protection (OTP): Thermal Shutdown and
Auto Thermal Recovery
Low Standby Power
Low System BOM Cost
Controller with External MOSFET
Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)
Halogen and Antimony Free. “Green” Device (Note 3)
Pin Assignments
Top View
1
2
3
6
4
OUT
COMP
GND 5VCC
FB
CS
Applications
General LED Lighting
Smart Connected LED Light Bulbs
Smart Connected LED Tubes, Panel Lights, Troffers, and Ceiling
Lights
High PFC and low THD power supply
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.
AL1788
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AL1788
NEW PROD UCT
Typical Applications Circuit
F1
VR1 R7
R5
R6
D1
AUX
C3
VCC
FB
COMP
C4 GNDCS
L1
C1 C2 R10 C5
Q1
D2
RCS
D3 C6
OUT R12
U1 AL1788
T1
DB1
R2
C7
Figure 1. AL1788 Controller Flyback Application
F1
VR1
L1
C1 C2 R7
Q1
R12
R5
R6
D2
L2
C6
R1
D1
R2
C4
U1 AL1788
OUTVCC
GNDCOMP
CSFB
DB1
RCS
C3 C7
Figure 2. AL1788 Controller Buck Application
AL1788
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AL1788
NEW PROD UCT
Pin Descriptions
Pin Name
Pin Number
Descriptions
CS
1
Primary Current Sensing
GND
2
Ground
COMP
3
Loop Compensation Pin
FB
4
Voltage Sensing Feedback
VCC
5
Power Supply
OUT
6
Gate Driver Output
Functional Block Diagram
CS
FB
VCC
OUT
GND
Leading Edge
Blanking Output
Control
Valley
Detector
Output Over
Voltage
Protection
+
+
-
-
+
+
-
-
Sawtooth
Generator
VCS_CL
PWM
Control
Logic
Over
Temperature
Protection
Under Voltage
Lockout
VCC Over
Voltage
Protection
VCLAMP
COMP
1
2
3
6
4
5
Figure 3. AL1788 Controller Functional Block Diagram
AL1788
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AL1788
NEW PROD UCT
Absolute Maximum Ratings (@TA = +25°C, unless otherwise specified.) (Note 4)
Symbol
Parameter
Rating
Unit
VIN
Input Voltage
-0.3 to 30
V
VCS
Voltage at CS
-0.3 to 7
V
VFB
Voltage at FB
-0.3 to 7
V
VCOMP
Voltage at COMP
-0.3 to 7
V
TJ
Junction Temperature
-40 to +150
°C
TST
Storage Temperature Range
-65 to +150
°C
TLEAD
Lead Temperature (Soldering, 10 sec)
+260
°C
PD
Power Dissipation (Note 5)
0.7
W
θJA
Thermal Resistance Junction-to-Ambient ) (Note 5)
160
°C /W
θJC
Thermal Resistance Junction-to-Case) (Note 5)
36
°C /W
ESD
HBM
Human Body Model ESD Protection
2,000
V
CDM
Charged Device Model ESD Protection
1,000
V
Notes:
4. Stresses greater than those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and
functional operation of the device at these or any other conditions beyond those indicated under “Recommended Operating Conditions” is not implied.
Exposure to “Absolute Maximum Ratings” for extended periods may affect device reliability. All voltages unless otherwise stated and measured with
respect to GND.
5. Device mounted on 1"x1" FR-4 MRP substrate PC board, 2oz cooper, with minimum recommended pad layout.
Recommended Operating Conditions (@TA = +25°C, unless otherwise specified.)
Symbol
Parameter
Min
Max
Unit
VCC
Input Voltage at VCC
9.0
25
V
TJ
Operating Junction Temperature
-40
+125
°C
AL1788
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AL1788
NEW PROD UCT
Electrical Characteristics (VCC=12V@TA = +25°C, unless otherwise specified.)
Symbol
Parameter
Condition
Min
Typ
Max
Unit
UVLO Section
VST
Startup Threshold Voltage
-
-
19
-
V
VOPR_MIN
Minimal Operating Voltage
After Turn On
7.0
-
8.5
V
VCC_OVP
VCC OVP Voltage
-
-
30
-
V
Standby Current Section
IST
Startup Current
VCC = VST -0.5V, Before Start-up
-
3
-
A
ICC_OPR
Operating Current
Static - No Switching (VCS=0.6V)
-
500
-
A
ICC_OVP
Shunt Current in OVP Mode
VCC =15V after VCC >VCC_OVP Triggered
-
2.5
-
mA
Drive Output Section
VOUT_CLAMP
Output Clamp Voltage
VCC =18V
12
13.5
15
V
VOL
Output Low Level
IGD_SINK=20mA, VCC =12V
-
-
1
V
tR
Output Voltage Rise Time
CL=1nF
-
100
-
ns
tF
Output Voltage Fall Time
CL=1nF
-
50
-
ns
tON_MIN
Minimum tON
-
-
0.7
-
s
tON_MAX
Maximum tON
-
-
17
-
s
tOFF_MIN
Minimum tOFF
-
-
1.2
-
s
tOFF_MAX
Maximum tOFF
-
-
40
-
s
fMAX
Maximum Frequency
-
-
120
-
kHz
CS Section
VCS_OCP
Primary Current OCP
-
-
0.5
-
V
COMP Section
GM_COMP
COMP Transconductance
-
-
100
-
A/V
IMAX_COMP_SOURCE
COMP Maximum Source
Current
VFB=0.8V
-
16
-
A
IMAX_COMP_SINK
COMP Maximum Sink Current
VFB=1.5V
-
16
-
A
VCOMP_PRO
COMP Protection Voltage
-
-
3.5
-
V
FB Section
VFB_CV
FB CV Threshold
-
1.15
1.2
1.25
V
VFB_OVP
FB OVP Threshold
-
-
1.35
-
V
Over Temperature Protection Section (Note 6)
TSH (Note 7)
Shutdown Temperature
-
-
+160
-
°C
THY
Temperature Hysteresis
-
-
+30
-
°C
Notes:
6. The over temperature protection parameters are guaranteed by design.
7. When the junction temperature reaches Thermal Shutdown Temperature (TSH), AL1788 enters Thermal Shutdown Mode with Hiccup Restart until junction
temperature drops below Shutdown Temperature minus Temperature Hysteresis (TSH- THY). Once junction temperature drops below (TSH- THY), AL1788 restarts
as in normal operation.
AL1788
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AL1788
NEW PROD UCT
Typical Performance Characteristics (@TA=+25°C, unless otherwise specified.)
12.0
14.0
16.0
18.0
20.0
22.0
-40 0 40 80 120
STARTUP VOLTAGE (V)
AMBIENT TEMPERATURE (℃)
Startup Voltage vs. Ambient Temperature
4.0
5.0
6.0
7.0
8.0
9.0
10.0
-40 040 80 120
MINIMUM OPERATING VOLTAGE (V)
AMBIENT TEMPERATURE (℃)
Minimum Operating Voltaqge vs. Ambient
Temperature
0.0
0.5
1.0
1.5
2.0
2.5
3.0
-40 040 80 120
STARTUP CURRENT (A)
AMBIENT TEMPERATURE (℃)
Startup Current vs. Ambient Temperature
0
100
200
300
400
500
600
-40℃0℃40℃80℃120℃
OPERATING CURRENT (A)
AMBIENT TEMPERATURE (℃)
Operating Current vs. Ambient Temperature
0.80
0.90
1.00
1.10
1.20
1.30
1.40
-40 040 80 120
FEEDBACK VOLTAGE (V)
AMBIENT TEMPERATURE (℃)
VFB_CV vs. Ambient Temperature
0.42
0.44
0.46
0.48
0.50
0.52
-40 0 40 80 120
PRIMARY CURRENT LIMIT VOLTAGE (V)
AMBIENT TEMPERATURE (℃)
Current Limit Voltage vs. Ambient Temperature
AL1788
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AL1788
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Functional Description and Application Information
The AL1788 is a high performance AC/DC Power Factor Correction (PFC) constant voltage controller targeting at LED lighting applications. It
operates with constant on time to achieve high power factor. And it adopts the Quasi-Resonant (QR) mode valley switching method to reduce
switching loss and improve EMI performance.
F1
VR1 R7
R5
R6
D1
AUX
C3
VCC
FB
COMP
C4 GNDCS
L1
C1 C2 R10 C5
Q1
D2
RCS
D3 C6
OUT R12
U1 AL1788
T1
DB1
R2
C7
Figure 4. AL1788 Controller Flyback Application
Start-up
After AC supply is powered on, the capacitor C3 across VCC and GND pin will be charged up by BUS voltage through a start-up resistor R7. Once
VCC reaches VST, the internal blocks start to work. VCC will be supplied by VBUS until the auxiliary winding of Flyback transformer could supply
enough energy to maintain VCC above VOPR_MIN. If VCC voltage is lower than VOPR_MIN , the switch will be turned off.
To accelerate the start-up process, the COMP voltage is internally pulled up and clamped high, leading to large MOSFET duty cycle and fast
climbing up of the output voltage. When the FB voltage reaches the reference voltage VFB_CV, the start-up process ends and the COMP voltage
turns to be modulated by the external compensation network.
VCC
VCOMP
PWM
VFB_CV
Internal COMP
VST
External COMP
VFB
Figure 5. Start Up Waveform
AL1788
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AL1788
NEW PROD UCT
Functional Description and Application Information (Cont.)
Constant Voltage Operation
As to constant-voltage (CV) operation mode, the AL1788 detects the auxiliary winding voltage at FB pin to regulate the output voltage. The
auxiliary winding voltage is coupled with secondary side winding voltage, so the auxiliary winding voltage at D3 conduction time is:
Where: VO is the output voltage
VD is the output rectifier diode forward voltage drop
NAUX is the turns of auxiliary winding
NS is turns of the secondary winding
VFB_CV is the output voltage setting
R5 and R6 that is shown as Figure 4 divide reflected voltage.
Figure 6. Auxiliary Voltage Waveform
Figure 6 shows the voltage waveform of the auxiliary winding. To accurately sample the divided auxiliary winding voltage, the AL1788 FB pin
delays a tSAMPLE time before sampling. And tDISCHARGE is the demagnetization time for the transformer.
Load Transition Operation
To obtain good load transition performance, the AL1788 COMP regulation mechanism is optimized. When the load changes from heavy to light
causing the FB voltage reaching VFB_OVP (typically 1.35V), the IC will pull down the COMP voltage and enter the max-off-time mode, accelerating
the discharge of the output voltage. When the load changes from light to heavy leading to the FB voltage touching 1.0V, the IC will charge up the
COMP voltage and raise the MOSFET on time, quickening the increase of the output voltage.
1.35V
VFB
VCS
VCOMP
Heavy load transition to light load
max-off-time mode
0 V
VFB
VCS
VCOMP
Light load transition to heavy load
1.0 V
0 V
Figure 7. Load Transition Waveform
AL1788
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Functional Description and Application Information (Cont.)
Protections
1. Output-Open Protection (VCC_OVP; VFB_OVP)
The output voltage is reflected by the voltage on transformer’s auxiliary winding. Both FB pin and VCC pin of IC have OVP function.
When there is a rapid line and load transient, the output voltage may exceed the regulated value. If VFB exceeds VFB_OVP, the OVP will be
triggered, and then AL1788 increases the OFF time to reduce output voltage.
If VCC exceeds VCC_OVP the OVP will be triggered, the switch will be turned off and VCC will be discharged. Once VCC is below VOPR_MIN, the IC will
shut down and power on again by BUS voltage through start up resistor.
2. Output Short Protection (OSP)
When the output is shorted, the output voltage is clamped to zero. The output voltage of the auxiliary winding, which is proportional to the
secondary winding, will drop down too. Once Vcc is below VOPR_MIN, the IC will shut down and power on again by the BUS voltage through the
startup resistor.
3. Over Current Protection (OCP)
AL1788 has a built-in cycle-by-cycle OCP of primary inductor current. When CS pin voltage reaches the voltage VCS_OCP, the switch will be turned
off until the next switch period. The maximum peak current (IPEAK (MAX)) of the inductor can be calculated as below:
Where: VCS_OCP means primary current clamp voltage that is 0.5V
RCS is current sense resister shown as Figure 4
4. Over Temperature Protection (OTP)
The AL1788 has built-in OTP function. When the junction temperature goes up to shut down temperature, the OTP will be triggered, the switch will
be shutdown. Until the junction temperature falls to the recovery temperature, the AL1788 will be restarted.
Operation Parameters Design
1. Setting the Current Sense Resistor
The current sense resistance can be calculated as following:
Where: IO_MEAN is the mean output current
KCS=1.5
RCS is current sense resister which is shown as Figure 4
VCS_OCP means primary current clamp voltage that is equal to 0.5V
NPS is the turns ratio of Flyback transformer
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Functional Description and Application Information (Cont.)
2. Setting Transformer Selection (T1)
NPS is limited by the electrical stress of the switch MOSFET, can be calculated by below formula.
Where: VMOS_DS is the breakdown voltage of the switch MOSFET
VIN_MAX is the maximum rated input voltage
VS is the overshoot voltage clamped by RCD snubber during OFF time
VO is the output voltage
VD is the forward voltage of secondary diode
NPS is the turn ratio of Flyback transformer;
For boundary conduction mode and constant on time method, the peak current of primary inductance can be calculated as below.
Where: VIN_RMS is the rate input voltage
IP is the primary inductance current
NPS is the turn ratio of Flyback transformer
IO_MEAN is the mean output current
VO is the output voltage;
The switching frequency is not constant for AL1788 due to QR operation. To set the minimum switching frequency fMIN at the crest of the minimum
AC input, primary inductance can be obtained by below formula.
Where: VIN_RMS is the rate input voltage
IP is the primary inductance current
NPS is the turn ratio of Flyback transformer
IO_MEAN is the mean output current; VO is the output voltage
fMIN is the minimum switching frequency at the crest of the minimum AC input
According to the Faraday’s Law, the winding number of the inductance can be calculated by:
Where: Ae is the core effective area
Bm is the maximum magnetic flux density
AL1788
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Ordering Information
AL1788 X - X
Product Name Package Packing
W6 : SOT26
(SC74R)
W6 : SOT26
(SC74R) 7: 7" Tape & Reel
7: 7" Tape & Reel
Part Number
Package Code
Packaging
7” Tape and Reel
Quantity
Part Number Suffix
AL1788W6-7
W6
SOT26 (SC74R) (Note 8)
3,000/Tape & Reel
-7
Note : 8. For packaging details, go to our website at https://www.diodes.com/design/support/packaging/diodes-packaging/.
Marking Information
SOT26 (SC74R)
1 2 3
6
7
4
XX Y W X
XX : Identification Code
Y : Year 0~9
X : Internal Code
( Top View )
5
W : Week : A~Z : 1~26 week;
a~z : 27~52 week; z represents
52 and 53 week
Part Number
Package
Identification Code
AL1788W6-7
SOT26 (SC74R)
A8
AL1788
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Package Outline Dimensions (All dimensions in mm.)
Please see http://www.diodes.com/package-outlines.html for the latest version.
SOT26 (SC74R)
SOT26 (SC74R)
Dim
Min
Max
Typ
A1
0.013
0.10
0.05
A2
1.00
1.30
1.10
A3
0.70
0.80
0.75
b
0.35
0.50
0.38
c
0.10
0.20
0.15
D
2.90
3.10
3.00
e
-
-
0.95
e1
-
-
1.90
E
2.70
3.00
2.80
E1
1.50
1.70
1.60
L
0.35
0.55
0.40
a
-
-
8°
a1
-
-
7°
All Dimensions in mm
Suggested Pad Layout
Please see http://www.diodes.com/package-outlines.html for the latest version.
SOT26 (SC74R)
Dimensions
Value (in mm)
C
2.40
C1
0.95
G
1.60
X
0.55
Y
0.80
Y1
3.20
a1
D
e
E1 E
b
A2 A1
Seating Plane
L
c
a
e1
A3
C1
Y1 G
X
Y
C
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INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
(AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION).
Diodes Incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements, corrections or other changes
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application or use of this document or any product described herein; neither does Diodes Incorporated convey any license under its patent or
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website, harmless against all damages.
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Should Customers purchase or use Diodes Incorporated products for any unintended or unauthorized application, Customers shall indemnify and
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This document is written in English but may be translated into multiple languages for reference. Only the English version of this document is the
final and determinative format released by Diodes Incorporated.
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Diodes Incorporated products are specifically not authorized for use as critical components in life support devices or systems without the express
written approval of the Chief Executive Officer of Diodes Incorporated. As used herein:
A. Life support devices or systems are devices or systems which:
1. are intended to implant into the body, or
2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the
labeling can be reasonably expected to result in significant injury to the user.
B. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the
failure of the life support device or to affect its safety or effectiveness.
Customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support devices or systems, and
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