BF1551
Offline Primary-side PWM + PFM Power Switch Controller
integrated with power BJT
BYD Microelectronics Co., Ltd.
General Description
Features
BF1551 is a high performance AC/DC power supply control
device which is operating in primary side sensing and
regulation .BF1551 includes an internal power BJT and is
designed for off-line power supplies within 10W output power.
It operates at PFM in CC mode and at PWM+PFM in CV
mode to providing accurate constant voltage, constant current
(CV/CC) regulation without requiring an opto-coupler and
secondary control circuitry. It has internal cable compensation
function for tight constant voltage regulation.
The BF1551 has a number of key built-in functions and
protection features, so that it can minimize the external
component count, simplify EMI design and lower the total bill
of material cost.
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Applications
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Primary Side Regulation eliminates Opto-coupler and
secondary CV/CC Control Circuitry
Multi-mode operation for highest overall efficiency
Internal 800V bipolar junction transistor(BJT)
± 5% Constant Voltage and high precision Constant
Current regulation at universal AC Input
No-load power consumption <100 mW at 230 Vac with
typical application circuit
Max output power 10W
Built-in Soft-Start circuit
Programmable Cable Drop Compensation
Low Start-up current (Max.5uA)
Built-in Frequency jitter easily meets global EMI
standards
Built-in Short Circuit Protection, output Over Voltage
Protection, Auxiliary Line Open Protection
Built-in Leading Edge Blanking (LEB)
Cycle-by-Cycle current limiting
Dynamic base current control
VDD Under Voltage Lockout with Hysteresis (UVLO)
DIP8 Package
Cell Phone Charger
Low Power Adaptor
Auxiliary Power for PC, TV etc.
LED Driver
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Typical Application
L1
4
6
V+
D7
D2
D1
D3
D4
C7
+
C1
+
C2
R3
1
5
R12
V-
R4
FR1
8
6
7
GND GND C
5
C
BF1551
3
D6
IC
COMP VDD VFB CS
1
2
3
4
R6
2
C5
C4 R7 R8
Output Power Table
85-265VAC
Product
Adapter
Open Frame
BF1551
10W
10W
Figure1：BF1551 Typical Application Circuit
Datasheet
WI-D06-J-0095 Rev. A/1
Page 1 of 7
BYD Microelectronics Co., Ltd.
BF1551
Block Diagram
COMP
VDD
Cable Drop
Compensation
Ref & Bias
start
2V
VFB
S
&
H
C
EA
PWM
&
PFM
LOGIC
Driver
Tds Sample
FS
VSS
Line Voltage
compensation
CS
Figure2：BF1551 Functional Block Diagram
Package Type
8 GND
COMP 1
VDD
2
VFB
3
CS
4
BF1551
XXXX
7 GND
6
C
5
C
Figure3：BF1551 Pin Configuration
BF1551: Product model
XXXX: Year Code, Week Code
Datasheet
WI-D06-J-0095 Rev. A/1
Page 2 of 7
BYD Microelectronics Co., Ltd.
BF1551
Pin Description
Pin Num
Pin Name
Description
1
COMP
Cable compensation
2
VDD
Power supply
3
VFB
Output feedback
4
CS
Primary current sense
5、6
C
Internal power BJT’s collector
7、8
GND
Ground
Absolute Maximum Ratings
Parameter
Symbol
Value
Unite
VDD pin input voltage
VDD
-0.3 to 40
V
Power dissipation
PD
400
mW
Collector base breakdown voltage
VCBO
800
V
Sense pin input voltage
VVFB
VIFB
-0.3 to 7
V
Lead temperature
TL
260
℃
Operating junction temperature
TJ
-40 to +125
℃
Storage temperature range
TSTJ
-55 to +150
℃
Attention: Stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device.
Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
Electrical Characteristic
Parameter
(TA = 25° C, unless otherwise noted)
Symbol
Test Conditions
Start-up current
IDD ST
VCC=15V
Operation current
Operation voltage
Min.
Typ.
Max.
Unit
2.5
5
µA
IDD op
390
600
µA
VDD op
14
Supply voltage
V
Turn-on threshold voltage
UVLO(ON)
15.5
17.5
19
V
Turn-off threshold voltage
UVLO(OFF)
6
7.1
8.2
V
Maximum operating frequency
fSW MAX
65
Minimum operating frequency
fSW MIN
0.6
Oscillator
KHz
1
1.7
KHz
Current Sensing
Leading edge blanking
Datasheet
TLEB
WI-D06-J-0095 Rev. A/1
470
ns
Page 3 of 7
BYD Microelectronics Co., Ltd.
BF1551
Maximum current sense detection voltage
VOCP MAX
Minimum current sense detection voltage
VOCP MIN
0.86
0.88
0.9
0.275
V
V
Voltage Sensing
Reference voltage for EA
VREF_EA
Reference voltage for over voltage protection
VREF_OV
1.914
1.934
1.954
2.4
V
V
Power Transistor
Collector base breakdown voltage
BVcbo
Ic=1mA
Collector emitter saturation voltage
Vcesat
Ic=500mA, Ib=100mA
hFE
Vce=5V, Ic=1A
DC current gain
800
V
0.3
20
V
35
Operation Description
● CC/CV Operation
The BF1551 uses PFM control mode in CC mode while PWM+PFM mode in CV mode. In charger applications, a discharged
battery starts charging in the CC mode, the IC switches to CV mode until the battery is nearly full charged. In order to achieve
constant output current and voltage, the working frequency and primary-side peak current will be changed with the feedback
voltage of VFB pin. The output voltage and current is given by:
VOUT  VREF_EA 
R6  R7 N S

 VD
R7
NA
(1)
Where VD indicates the drop voltage of output Diode, N S /N A indicates the transformer secondary-auxiliary turns ratio.
I OUT 
1 3 NP
 
 IP
2 7 NS
(2)
Where I P indicates the maximum peak current of primary winding, N P /N S indicates the primary-secondary turns ratio.
●Cycle-by-Cycle Current Limiting
The primary-side current flow through the sense-resistor and make the voltage on IFB pin ramp up. When the voltage exceeds
the internal threshold voltage value, the power BJT will be turned off immediately. The threshold voltage is changing gradually
in CV mode while constant in CC mode.
●Soft Start
A built-in soft start circuit is applied at start-up state. Once
the VDD reaches UVLO(ON), the primary-side peak current voltage threshold will ramp up from 0.275V to 0.9V gradually
because of the soft start circuit.
●Voltage Protection Function
The BF1551 includes such a function that protect against
output over-voltage and under-voltage, which could be monitored by VFB pin and VDD pin. If the voltage at VFB pin exceeds
the over-voltage threshold, the external power BJT will be turned off immediately and the controller will restart. Once VDD
Datasheet
WI-D06-J-0095 Rev. A/1
Page 4 of 7
BYD Microelectronics Co., Ltd.
BF1551
drops below the UVLO(OFF) threshold, the controller will reset itself and go into a new start cycle. The controller will continue
the start cycle until the error condition is removed.
●Output Cable Drop Compensation
The BF1551 includes programmable output cable compensation to achieve good load regulation. The cable drop
compensation is programmable by changing the value of the resistance R6. The maximum compensation voltage VCOMP is
given by:
VCOMP  I COMP  R6 
NS
NA
(3)
Where I COMP  34uA is the maximum compensation current which generated by an internal current source.
●Built-in line-voltage compensation
BF1551 incorporates an innovative method to compensate the different line voltage , VFB pin detect voltage on the Ton
period , then converts it to the current compensation.
VC  2  Vline 
N A 1 8.3


N P R6 185
(4)
●Dynamic base current control
BF1551 directly drives a BJT switching device with base current control to optimize performance. The BJT base current
ranges from 10mA to 28mA,the base current is related to VIPK ,as shown in figure 4
30
Base Drive Current (mA)
25
20
15
10
5
0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
VIPK (V)
Figure4: Base Drive Current vs. VIPK
Datasheet
WI-D06-J-0095 Rev. A/1
Page 5 of 7
BYD Microelectronics Co., Ltd.
BF1551
Package Outline
DIP8
Packing
package
pcs/tube
tube/ inner box
inner box/ carton
pcs/carton
tube
50
40
10
20000
Datasheet
WI-D06-J-0095 Rev. A/1
Page 6 of 7
BYD Microelectronics Co., Ltd.
BF1551
RESTRICTIONS ON PRODUCT USE
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The information contained herein is subject to change without notice.
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BYD Microelectronics Co., Ltd. (short for BME) exerts the greatest possible effort to ensure high quality and reliability.
Nevertheless, semiconductor devices in general can malfunction or fail due to their inherent electrical sensitivity and vulnerability
to physical stress. It is the responsibility of the buyer, when utilizing BME products, to comply with the standards of safety in
making a safe design for the entire system, including redundancy, fire-prevention measures, and malfunction prevention, to
prevent any accidents, fires, or community damage that may ensue. In developing your designs, please ensure that BME products
are used within specified operating ranges as set forth in the most recent BME products specifications.
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The BME products listed in this document are intended for usage in general electronics applications (computer, personal
equipment, office equipment, measuring equipment, industrial robotics, domestic appliances, etc.). These BME products are
neither intended nor warranted for usage in equipment that requires extraordinarily high quality and/or reliability or a malfunction or
failure of which may cause loss of human life or bodily injury (“Unintended Usage”). Unintended Usage include atomic energy
control instruments, airplane or spaceship instruments, transportation instruments, traffic signal instruments, combustion control
instruments, medical instruments, all types of safety devices, etc.. Unintended Usage of BME products listed in this document shall
be made at the customer’s own risk.
Datasheet
WI-D06-J-0094
Rev. A/1
Page 7 of 7