參數(shù)資料
型號(hào): NCP1212PG
廠商: ON SEMICONDUCTOR
元件分類: 穩(wěn)壓器
英文描述: Current Mode PWM Controller for Both Forward and Flyback Converters
中文描述: 1 A SWITCHING CONTROLLER, 200 kHz SWITCHING FREQ-MAX, PDIP8
封裝: LEAD FREE, PLASTIC, DIP-8
文件頁(yè)數(shù): 18/22頁(yè)
文件大?。?/td> 200K
代理商: NCP1212PG
NCP1212
http://onsemi.com
18
Figure 42. Brownout Detect Waveforms
Channel 1: The MOSFET’s V
DS
Switching Waveform
Channel 2: Primary Bulk Capacitor Voltage
Channel 3: BOK Pin Voltage
Experimental results for the Brownout action were shown
in Figure 42. From the captured waveforms, it can be noted
that the Brownout Input Threshold Voltage is 1.21 V and
Brownout Hysteresis Voltage is 1.36 V at BOK pin.
4. Improving Light Load and No Load Regulation for
High Power Applications
For high power applications, limited by the dynamic
range of the control circuitry, i.e. the control
feedback is limited by the swing of the optocoupler.
When V
FB
reaches about 0.1 V at light load
conditions, it no longer has the means to further
reduce that voltage because of the saturation of the
optocoupler. At light load or no load conditions, the
primary current is very small and as the current
sensing resistor is also small for high power
applications, the current sense feedback voltage will
be much smaller than 0.1 V. Consequently, the
control will force to acquire maximum Duty Cycle
operation and the output will increase without
control.
In order to improve the poor regulation at light load,
a small circuit is added as shown in Figure 43. With
the additional circuitry, when V
FB
falls below 0.1 V,
Q2 will drive additional offset current to CS pin and
modify the current sensing voltage, V
CS
. For V
FB
higher than 0.1 V at normal load operation, Q2 will
be turned off due to limited V
be.
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