English

BL8326
PFC Controller with PSR for LED Driver
Features
General Description

BL8326 is a single stage flyback and primary
side regulation constant current controller, targeting
at AC-DC LED lighting. BL8326 integrates active
power factor correction and works in boundary
conduction mode (BCM) which can minimize the
switching loss, increasing efficiency. BL8326
enhances the LED current accuracy for line voltage
variation and output voltage variation in universal
input voltage range (85Vac ~ 265Vac). BL8326
removes the secondary side feedback circuit to
simplify the LED lighting system.
BL8326 provides various protections, such as
output open or short circuit protection, VCC or FB
over voltage protection, VCC under voltage
protection, over temperature protection, over
current protection, etc., to improve system
reliability, the system can recovers from all the
protection automatically.
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Primary Side Regulation constant current
controller, eliminates opto-coupler.
Single stage flyback PFC controller with
high PF and low THD
Boundary Conduction Mode (BCM) with
PFC
±3% LED output current accuracy
Excellent line voltage compensation and
output voltage compensation
Cycle-by-cycle current limiting
Start up with soft-start process
under voltage & over voltage protection
Secondary-side open or short protection
LED current decreases with temperature
increasing in range 110-150℃
SOP8 package available
Meet the requirement of RoHS
Application
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Pinout (top view)
Retro-fit lamps, e.g. GU10/E27
LED PAR30, PAR38 lamp
Isolation AC/DC LED driver application
SOP-8
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BL8326
PFC Controller with PSR for LED Driver
PIN Description
Pin No.
Pin Name
Pin Description
1
CS
Current sense pin, connect the sense resistor (RCS) across
this pin and GND
2
GND
Ground pin
3
COMP
Loop compensation pin，connect a capacitor across this pin
and GND to stabilize the control loop
4
LN
Line voltage sample pin
5
FB
Secondary-side current zero-crossing detection pin.
6
VCC
Power supply pin
7
ST
Chip start-up pin
8
OUT
Source driver pin. Connect this pin to the source of the
external power MOSFET
Typical Application
Note: 1. CST, CVCC, CC should be placed as close as possible to ST, VCC, COMP pin respectively.
2. The resistor RH, RL should be placed as close as possible to FB pin, and the resistor terminal
should be placed as far as possible to transformer active terminal.
3. The GND terminal of the RCS resistor, chip GND pin and the GND terminal of the other small
signal should be connected to the GND terminal of the CIN respectively, and the path should
be as short as possible.
4. To improve EMI performance, should minimize the area of the power current loop.
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BL8326
PFC Controller with PSR for LED Driver
Component Recommended
Symbol
Parameter
Recommended value
Unit
CST
Start-up capcitor
330/470
nF
CVCC
VCC capcitor
2.2
uF
CC
Compensation capacitor for loop stability
1
uF
RST
Start-up resistor
1/1.5
MΩ
RCS
Current sample resistor
N*150(mV)/ILED(mA) Note
Ω
Note: N is the ratio of primary winding and secondary winding
Absolute Maximum Ratings
Symbol
Parameter
Value
Unit
ST
Start-up voltage
0~20
V
VCC
Power supply voltage
0 ~ 22
V
CS/COMP/LN/FB
Pins for low operating voltage
0~6
V
PDmax
Maximum Power Dissipation
0.45
W
ΘJA
Package Thermal Resistance
145
℃/W
TJ
Junction Temperature Range
-40 ~ 150
℃
TSTG
Storage Temperature Range
-55~ 150
℃
Note:
* PDmax: The temperature difference between junction temperature (TJ) and ambient temperature (TA) is 100℃。
* Stress beyond the “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only.
Functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the
speciation is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliablity.
Recommended Operating Condition
Symbol
Parameter
Min
Max
Unit
VCC
VCC supply voltage
11.5
17.5
V
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BL8326
PFC Controller with PSR for LED Driver
Electrical Characteristics
Symbol
Parameter
Test Conditions
Min
Typ
Max
Unit
16
17
18
V
Start-up Voltage (ST Pin)
VST_ON
ST Start-up voltage
1mA，VCC=10V
VST_HYS
ST hysteresis voltage
VCC=14
2
IST_ON
ST Start-up current
VCC=10
20
35
uA
IST_OP
ST operating current
VCC=14
35
60
uA
V
Power Supply Voltage (VCC Pin)
VCC_ON
VCC start-up voltage
VCC increase
10
11
12
V
VCC_UVLO
VCC under voltage
VCC decrease
5.2
5.8
6.5
V
VCC_HOLD
VCC hold voltage
VCC decrease
8.5
9
9.5
V
ICC_UVLO
VCC current when VCC under
VCC increase，
40
70
uA
voltage
VCC=10V
VCC quiescent current
No switching,
320
600
uA
IQ
VCC=14V
ICC
VCC operating current
VCC_OVP
VCC over voltage
FOP=60kHz
600
uA
20
V
Feedback (FB Pin)
VFB_FALL
FB falling threshold voltage
FB falling
0.4
V
VFB_HYS
FB hysteresis voltage
FB rising
0.6
V
VFB_OVP
FB over voltage protection
5.5
V
TOFF_MIN
Minimum off time
4.0
us
TOFF_MAX
Maximum off time
120
us
Current Sense (CS Pin）
TLEB_CS
Lead edge block time
350
ns
TDELAY
Protection response delay
180
ns
Loop Compensation (COMP Pin)
VREF
Built in reference voltage
VCOMP_LO
COMP start-up voltage
VCOMP
COMP linear range
VCOMP_OVP
Output short threshold voltage
0.294
0.300
0.306
1.5
1.5
V
V
3.5
4.5
V
V
Line Voltage Sample (LN Pin)
VLN
LN linear range
0
2.5
V
Drive Stage (OUT Pin)
RDS_ON
Resistance of the internal
VCC=14V
500
mΩ
source-drive MOS
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BL8326
PFC Controller with PSR for LED Driver
Block Diagram
Applications Information
BL8326 is a Primary-side Regulator for AC-DC
LED driver. The LED current can be regulated
accurately through sensing the primary side
information. BL8326 integrates active power factor
correction and works in boundary conduction mode
(BCM).
1. Constant current control
According to the relationship of the primary side
peak current and the secondary side current,
BL8326 regulates accurately LED current through
sensing the primary side information. The LED
current can be easily set as following:
Where N is the ratio of primary winding and
secondary winding; Vref (=300mV) is the internal
reference voltage and RCS is an external current
sensing resistor.
2. Start-up
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After AC supply, the capacitor CST across ST
and GND pin is charged up by line voltage
through a start up resistor RST. The ST voltage is
clamped to 15V once ST voltage rises up to 17V
and the internal operating voltage sets up. A
small capacitor (CST) can be used to shorten the
system start-up time.
The line voltage charges capacitor CVCC
through the external MOSFET, OUT pin and the
internal charge circuit. When VCC voltage rises
up to VCC_ON, chip turns off the internal charge
circuit, and VCC is supplied by the auxiliary
winding. The system starts with soft-start mode
to avoid output overshoot. In the soft-start mode,
the chip operates at 8kHz switching frequency.
If the output voltage is lower, the internal
charge circuit works and charges CVCC capacitor.
In this case, the chip operating current is
supplied by the internal charge circuit, not
auxiliary winding.
Total 6 Page
BL8326
PFC Controller with PSR for LED Driver
VCC charge process
3. Power Factor Correction
When the AC line voltage is changed according
to the sine wave, the comparator forces the peak
current of primary side tracking trajectory of AC
line. In every cycle, the envelope of the primary
side peak current is proportional to the
instantaneous AC line, thus the controller achieve
high power factor which is closed to 1. Because of
the PFC voltage control loop, the converter output
ripple is very big, and the frequency is 100 Hz, the
same as the sine wave.
4. Feedback circuit
BL8326 detects the end of demagnetization
through sensing the voltage across the auxiliary
winding by a resistor divider. It is determined for
the ZCD(zero-current-detected) time when FB
voltage is down to 0.4v from the voltage above 1v,
the power MOSFET will be turned on. If the
secondary-side short circuit happens, this will cause
a lower output voltage, the FB voltage would not
exceed 1V, in this case, ZCD can’t be detected, the
power MOSFET will be turned on again after
TOFF_MAX (≈120us) at the end of the magnetization.
If FB pin’s voltage is detected above 5.5V, the
over voltage protection will be trigged.
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5. Line voltage compensation and output
voltage compensation
Due to the same propagation delay, the LED
current increases with input voltage increasing.
To obtain a constant LED current independent
of input voltage, a small compensation voltage
(VCCS) proportional to AC voltage is involved,
and can be adjusted by the upper resistor of the
divider connected to FB pin.
An output voltage compensation circuit is
built in also to archive the constant LED current
independent of output voltage.
6. Over voltage protection
BL8326 immediately turns off the power
MOSFET once VCC voltage is over 20V, such
as in the case of LED open. A restart process
will be kicked off when the VCC voltage drops
below the UVLO threshold.
7. Secondary side short circuit protection
If secondary-side short-circuits, the system
operates at 8kHz to minimize the VCC current,
and the COMP voltage increase. The drive
switching will be turned off once COMP voltage
is up to 4.5V.
8. Over Current Protection
BL8326 will turn off the power MOSFET if
RCS short or transformer is saturation.
Total 6 Page
BL8326
PFC Controller with PSR for LED Driver
Package Outline: SOP-8
c
E
E1
L
D
?
e
A
A2
A1
b
Dimensions（mm）
Symbol
Min
Typ
Max
A
1.350
1.10
1.750
A1
0.100
---
0.250
A2
1.350
1.10
1.550
b
0.330
0.40
0.510
c
0.170
0.125
0.250
D
4.700
2.90
5.100
E
3.800
1.60
4.000
E1
5.800
e
---
1.27
---
L
0.400
---
1.270
θ
0°
5°
8°
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