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Detail Description
RS2136 is a cost effective PWM power switch optimized for off‐line low power AC/DC applications including battery chargers
and adaptors. It operates in primary side sensing and regulation, thus opto‐coupler and 431 are not required. Proprietary
built‐in CV and CC control can achieve high precision CC/CV control meeting most adaptor and charger application
requirements.
Startup Current and Start up Control
Startup current of RS2136 is designed to be very low so that VDD could be charged up above UVLO threshold and starts up
quickly. A large value startup resistor can therefore be used to minimize the power loss in application.
Operating Current
The Operating current of RS2136 is as low as 2.5mA. Good efficiency is achieved with the low operating current together with
Multi‐mode control features.
Soft Start
RS2136 features an internal soft start to minimize the component electrical over‐stress during power on startup. As soon as
VDD reaches UVLO (OFF), the control algorithm will ramp peak current voltage threshold gradually from nearly zero to
normal setting of 0.90V. Every restart is a soft start.
CC/CV Operation
RS2136 is designed to produce good CC/CV control characteristic as shown in the Fig. 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.
In an AC/DC adapter, the normal operation occurs only on the 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,
RS2136 will regulate the output current constant regardless of the output voltage drop.
Principle of Operation
To support RS2136 proprietary CC/CV control, system needs to be designed in DCM mode for flyback system (Refer to Typical
Application Diagram).
In the DCM flyback converter, the output voltage can be sensed via the auxiliary winding. During MOSFET turn‐on time, the
load current is supplied from the output filter capacitor C
O
. The current in the primary winding ramps up. When MOSFET
turns off, the primary current transfers to the secondary at the amplitude of
I
S
=
N
P
×
I
P
N
S
The auxiliary voltage reflects the output voltage as shown in fig.2 and it is given by
V
AUX
=
N
AUX
×
(V
O
+ Δ
V)
N
S
Where ΔV indicates the drop voltage of the output Diode.
DS‐RS2136‐03
September,
2009
www.Orister.com
ORISTER [ ORISTER CORPORATION ]
