BF1550
Offline Primary-side PWM + PFM Power Switch Controller
Integrated with power BJT
BYD Microelectronics Co., Ltd.
General Description
Features
BF1550 is a high performance AC/DC power supply control
device which is operating in primary side sensing and
regulation .BF1550 includes an internal power BJT and is
designed for off-line power supplies within 6W 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 BF1550 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.

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
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)
SOP7 Package
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Applications
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Cell Phone Charger
Low Power Adaptor
Auxiliary Power for PC, TV etc.
LED Driver
Typical Application
L1
4
6
V+
D7
D2
D1
D3
D4
C7
C1
+
+
C2
R3
1
5
R12
V-
R4
FR1
7
6
5
GND
C
C
BF1550
IC
COMP VDD VFB CS
3
1
D6
2
3
4
Output Power Table
R6
2
C5
C4 R7
R8
Product
BF1550
Adapter
5W
85-265VAC
Open Frame
5W
Figure1：BF1550 Typical Application Circuit
Datasheet
WI-D06-J-0094
Rev.A/1
Page 1 of 7
BYD Microelectronics Co., Ltd.
BF1550
Block Diagram
COMP
VDD
Cable Drop
Compensation
Ref & Bias
Start
2V
C
EA
S
&
H
VFB
PWM
&
PFM
Logic
Driver
Tds Sample
FS
Line Voltage
compensation
VSS
CS
Figure2：BF1550 Functional Block Diagram
Package Type
7 GND
COMP 1
VDD
2
VFB
3
CS
4
BF1550
XXXX
6
C
5
C
Figure3：BF1550 Pin Configuration
BF1550: Product model
XXXX: Year Code, Week Code
Pin Description
Pin No.
Pin Name
Description
1
COMP
Cable compensation
2
VDD
Power supply
3
VFB
Output feedback
4
CS
Primary current sense
5
C
Internal power BJT’s collector
6
C
Internal power BJT’s collector
7
GND
Ground
Datasheet
WI-D06-J-0094
Rev.A/1
Page 2 of 7
BYD Microelectronics Co., Ltd.
BF1550
Absolute Maximum Ratings
Parameter
Symbol
Value
Unite
Primary peak current
IPK
400
mA
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
(TA = 25° C, unless otherwise noted)
Parameter
Symbol
Test Conditions
Start-up current
IDD ST
Operation current
IDD op
Operation voltage
VDD op
Min.
Typ.
Max.
Unit
VCC=15V
2.5
5
µA
VCC=19V
390
600
µA
Supply voltage
14
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
TLEB
470
Maximum current sense detection voltage
VOCP MAX
Minimum current sense detection voltage
VOCP MIN
0.86
0.88
ns
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=100mA
DC current gain
Datasheet
WI-D06-J-0094
Rev.A/1
800
V
0.5
20
30
Page 3 of 7
V
BYD Microelectronics Co., Ltd.
BF1550
Operation Description
● CC/CV Operation
The BF1550 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 BF1550 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 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 BF1550 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
Datasheet
WI-D06-J-0094
Rev.A/1
Page 4 of 7
BYD Microelectronics Co., Ltd.
BF1550
BF1550 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
BF1550 directly drives a BJT switching device with base current control to optimize performance. The BJT base current
ranges from 8mA to 20mA,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-0094
Rev.A/1
Page 5 of 7
BYD Microelectronics Co., Ltd.
BF1550
Package Outline
SOP7
Packing
MBB packing
13”reel: Pizza box 360mm*360mm*40mm.carton 380mm*380*mm*330mm.2500PCS per reel.
Datasheet
WI-D06-J-0094
Rev.A/1
Page 6 of 7
BYD Microelectronics Co., Ltd.
BF1550
RESTRICTIONS ON PRODUCT USE

The information contained herein is subject to change without notice.

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.

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