RS2201S Orister Corporation, RS2201S Datasheet - Page 2

• Manufacturer Part Number: RS2201S
• Description: Switching Power Supply Controller
• Manufacturer: Orister Corporation

Typical Application Circuit
Operation description
DS-RS2201-01
In open cycle, OB provides the base current for power transistor, OE pulls down the emitter of power transistor to IS and
OB adopts slop current drive (OB open current is IS function, when IS=0V,OB open current is about 40mA, and OB open
current is increasing with IS linear increasing. When IS increases 0.6V, OB open current is about 120mA. This
characteristics makes use of output current of OB effectively and reduces power consumption of RS2201). If IS detects the
FB designated current, it enters closed cycle. In closed cycle, OB pulls down, the power transistor is not be turn off
immediately but OE clamps 1.5V (after power transistor is turn off, the base is reverse bias, the breakdown voltage of
power transistor is improved). In the open or closed cycle, if power transistor is detected to exceed upper limit current, the
upper limit current trigger will set firstly and forces FB to pull down, duty cycle reduced, so to protect power transistor and
transformer. In the next closed cycle start-up time, or when FB is less than 1.8V, upper current trigger resets. In addition,
RS2201 is built in thermal protection, when the internal temperature is above 140 , it
that the temperature of RS2201 will not exceed 150 .
during the maximum duty cycle or the continual current mode of RS2201.
Initially, after power up, no output of VR. FB pull-up current source is turn off. OE inputs start-up current from power
transistor to VCC. OB controls the base current of power transistor and limits the collector current (start-up accept current
of RS2201) of power transistor so to safeguard the power transistor. When the VCC voltage rises to 7.8V, the start-up
phase completes and goes to the normal operation.
In normal operation, VCC voltage must keep 4.75~9.8V, VR outputs 2.5V reference voltage. FB pull-up current source
turns on. Oscillator outputs OSC1 to decide the maximum duty cycle and OSC2 to trigger power supply entering the open
cycle and cover spike value of power transistor start-up current. If FB is less than 1.8V(about 1.2-1.8V), the less the FB is,
the wider the oscillation cycle is.（This characteristics reduces the standby consumption of the switching power supply）.
If external feedback intends to get VCC greater than 9.8V, the internal feedback circuit regular VCC on 9.8V.（Making use
of this characteristics to stable output voltage no using external feedback circuit, but the regulating is not precise）.
If VCC reduces to 4.4V, oscillator is turn off, OSC1 OSC2 low level, power supply keeps closed cycle. when VCC
continually reduces to about 4.0 V , RS2201 enters start-up phase again.
Nov, 2007
℃ Slop compensation is built in to stabilization open/closed cycle
℃
will widen the cycle of oscillator, so
www.Orister.com
Page No. : 2/2