High Precision CC/CV Primary-Side PWM Controller
OB2538 is a high performance offline PWM Power
switch for low power AC/DC charger and adaptor
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.
OB2538 offers power on soft start control and
protection coverage with auto-recovery features
including Cycle-by-Cycle current limiting, VDD
OVP, VDD clamp and UVLO. Excellent EMI
performance is achieved with On-Bright
proprietary frequency shuffling technique.
High precision constant voltage (CV) and constant
current (CC) can be achieved by OB2538.
5% Constant Voltage Regulation, 5%
Constant Current Regulation at Universal AC
Primary-side Sensing and Regulation Without
TL431 and Opto-coupler
Programmable CV and CC Regulation
Adjustable Constant Current and Output
Built-in Secondary Constant Current Control
with Primary Side Feedback
Built-in Adaptive Current Peak Regulation
Built-in Primary winding inductance
Programmable Cable drop Compensation
Power on Soft-start
Built-in Leading Edge Blanking (LEB)
Cycle-by-Cycle Current Limiting
VDD Under Voltage Lockout with Hysteresis
Low Power AC/DC offline SMPS for
Cell Phone Charger
Digital Cameras Charger
Small Power Adaptor
Auxiliary Power for PC, TV etc.
Linear Regulator/RCC Replacement
OB2538 is offered in DIP8 package.
Fig.1. Typical CC/CV Curve