参数资料
型号: NCP1238AD65R2G
厂商: ON Semiconductor
文件页数: 31/38页
文件大小: 0K
描述: IC REG CTRLR FLYBACK PWM 7SOIC
标准包装: 1
PWM 型: 电流模式
输出数: 1
频率 - 最大: 70kHz
占空比: 85%
电源电压: 9.5 V ~ 28 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: -40°C ~ 125°C
封装/外壳: 8-SOIC(0.154",3.90mm 宽)7 引线
包装: 标准包装
其它名称: NCP1238AD65R2GOSDKR
NCP1238
LOW LOAD OPERATION
Frequency Foldback
In order to improve the efficiency in light load conditions,
the frequency of the internal oscillator is linearly reduced
from its nominal value down to f OSC(min) . This frequency
foldback starts when the voltage on FB pin V FB goes below
V FB(fold) , and is complete before V FB reaches V skip(in) ,
whatever the nominal switching frequency option is. The
current ? mode control is still active while the oscillator
frequency decreases, but the frequency jittering is off.
Note that the frequency foldback is disabled if the
controller runs at its maximum duty cycle.
f OSC
Nominal f OSC
Skip
f OSC(min)
FB
V skip(in)
V FB(fold)
Figure 59. Frequency Foldback when the FB Voltage Decreases
Skip Cycle Mode with Soft ? Skip
t SSKIP
+
?
+
V skip
Soft ? skip ramp
Reset
Sawtooth
Oscillator
DC MAX
FB
CS
K FB
blanking
t LEB
+
?
?
+
S
Q
R
DRV stage
Figure 60. Skip Cycle with Soft ? Skip Schematic
When V FB reaches V skip(in) while decreasing, the skip
mode is activated: the driver stops, and the internal
consumption of the controller is decreased. While V FB is
below V skip(out) , the controller remains in this state. When
V FB crosses V skip(out) , the DRV pin starts to pulse again, and
the controller restarts with a short Soft ? Skip duration
(t SSKIP ). The soft ? skip imposes the peak current from nearly
0, in a voltage ? mode manner: it doesn’t have the same
behavior as the startup soft ? start which is current ? mode
driven.
http://onsemi.com
31
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