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부품번호 | OB2550 기능 |
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기능 | High Precision CC/CV Primary-Side Controller | ||
제조업체 | On-Bright Electronics | ||
로고 | |||
OB2550
High Precision CC/CV Primary-Side Controller
GENERAL DESCRIPTION
OB2550 is a high performance offline PSR
controller for low power AC/DC charger and
adapter applications. It operates in primary-side
sensing and regulation. Consequently,
opto-coupler and TL431 could be eliminated.
Proprietary Constant Voltage (CV) and Constant
Current (CC) control is integrated as shown in the
figure below.
In CC control, the current and output power setting
can be adjusted externally by the sense resistor
Rs at CS pin. In CV control, multi-mode operations
are utilized to achieve high performance and high
efficiency. In addition, good load regulation is
achieved by the built-in cable drop compensation.
Device operates in PFM in CC mode as well at
large load condition and it operates in PWM with
frequency reduction at light/medium load. The chip
consumes very low operation current, it can
achieve less than 30mW standby power to meet
strict standby power standard.
OB2550 offers comprehensive protection
coverage with auto-recovery features including
Cycle-by-Cycle current limiting, VDD over voltage
protection, feedback loop open protection, short
circuit protection, built-in leading edge blanking,
VDD under voltage lockout (UVLO), OTP etc.
OB2550 is offered in SOT23-6 package.
Figure.1. Typical CC/CV Curve
TYPICAL APPLICATION
Product Specification
FEATURES
Primary-side Sensing and Regulation Without
TL431 and Opto-coupler
High Precision Constant Voltage and Current
Regulation at Universal AC Input
Multi-mode PWM/PFM operation for efficiency
improving
Meet 30mW no load standby power standard
Good dynamic response
Programmable CV and CC Regulation
Built-in Line Voltage and Primary Winding
Inductance Compensation
Programmable Cable Drop Compensation
No Need For Control Loop Compensation
Precise Internal Over Temperature Protection
Audio Noise Free Operation
Drive BJT Switch
Built-in Leading Edge Blanking (LEB)
Ultra Low Start-up Current (Typ. 1uA) and Low
Operating Current (Typ. 360uA)
Comprehensive Protection Coverage with
auto-recovery
VDD Over Voltage Protection
VDD Under Voltage Lockout with
Hysteresis (UVLO)
Cycle-by-Cycle Current Limiting
Feedback Loop Open Protection
Output Short Circuit Protection
Over Temperature Protection (OTP)
APPLICATIONS
Low Power AC/DC offline SMPS for
Cell Phone Charger
Digital Cameras Charger
Small Power Adapter
Auxiliary Power for PC, TV etc.
Linear Regulator/RCC Replacement
©On-Bright Electronics
Confidential
-1-
Preliminary datasheet
OB_DOC_DS_255000
BLOCK DIAGRAM
OB2550
High Precision CC/CV Primary-Side Controller
©On-Bright Electronics
Confidential
-4-
Preliminary datasheet
OB_DOC_DS_255000
4페이지 OB2550
High Precision CC/CV Primary-Side Controller
OPERATION DESCRIPTION
OB2550 is a cost effective PSR controller
optimized for off-line low power AC/DC
applications including battery chargers. It
operates in primary side sensing and regulation,
thus opto-coupler and TL431 are not required.
Proprietary built-in CV and CC control can
achieve high precision CC/CV control meeting
most charger application requirements.
Fast Start up Control
Startup current of OB2550 is designed to be
very low so that VDD could be charged up
above UVLO threshold and starts up quickly.
The startup resister Rstart from the rectified
high voltage DC rail supplies current to the
base of the NPN transistor Q1. An amplified
emitter current charge VDD capacitor through
diode D1 from ED pin to VDD pin. Thus, a large
value startup resistor can therefore be used to
minimize the power loss in application.
+
+
Principle of Operation
To support OB2550 proprietary CC/CV control,
system needs to be designed in DCM mode for
flyback system (Refer to Typical Application
Diagram on page1).
In the DCM flyback converter, the output voltage
can be sensed via the auxiliary winding. During
BJT turn-on time, the load current is supplied from
the output filter capacitor, Co. The current in the
primary winding ramps up. When BJT turns off, the
energy stored in the primary winding is transferred
to the secondary side such that the current in the
secondary winding is
IS
NP
NS
IP
(1)
The auxiliary voltage reflects the output voltage as
shown in Figure.2 and it is given by
V AUX
N AUX
NS
(VO
V )
(2)
Where V indicates the drop voltage of the
output Diode.
Operating Current
The Operating current of OB2550 is as low as
650uA. Good efficiency and 30mW standby
power is achieved with the low operating
current.
CC/CV Operation
OB2550 is designed to produce good CC/CV
control characteristic as shown in the Figure. 1.
In charger applications, a discharged battery
charging starts in the CC portion of the curve
until it is nearly full charged and smoothly
switches to operate in CV portion of the curve.
The CC portion provides output current limiting.
In CV operation, the output voltage is regulated
through the primary side control. In CC
operation mode, OB2550 will regulate the
output current constant regardless of the output
voltage drop.
Figure.2. Auxiliary voltage waveform
Via a resistor divider connected between the
auxiliary winding and FB (pin 1), the auxiliary
voltage is sampled at the middle of the
de-magnetization and it is hold until the next
sampling. The sampled voltage is compared with
Vref (2.5V) and the error is amplified. The error
amplifier output reflects the load condition and
controls the switching off time to regulate the
output voltage, thus constant output voltage can
be achieved.
When the sampled voltage is below Vref and the
error amplifier output reaches its minimum, the
switching frequency is controlled by the sampled
voltage to regulate the output current, thus the
©On-Bright Electronics
Confidential
-7-
Preliminary datasheet
OB_DOC_DS_255000
7페이지 | |||
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부품번호 | 상세설명 및 기능 | 제조사 |
OB2550 | High Precision CC/CV Primary-Side Controller | On-Bright Electronics |
DataSheet.kr | 2020 | 연락처 | 링크모음 | 검색 | 사이트맵 |