參數(shù)資料
型號(hào)： NCP1239
廠商： ON SEMICONDUCTOR
英文描述： Low−Standby High Performance PWM Controller
文件頁(yè)數(shù)： 28/38頁(yè)
文件大?。?/td> 1145K
代理商： NCP1239
NCP1239
http://onsemi.com
28
Figure 48.
ac line
Preconverter
PFC
Cbulk
+
Cfil
Rupper
Rlower
5
to converter
Rectified AC Line Sensing
Input
filtering
Capacitor
A second option to directly sense the mains
This second option that directly senses the input voltage
(see Figure 48), enables a more direct undermains
detection. Even in a brownout conditions, the PFC
preconverter may be able to maintain a sufficient bulk
voltage, possibly at the price of some excessive stress.
Measuring the rectified AC line instead of the bulk voltage,
the NCP1239 more surely protects the PFC stage in
brownout conditions.
Using:
Rlower = 10 k ,
Rupper = 2. 39 M ,
Cfil = 1 F,
One obtains the following voltage thresholds:
Vtrip = 85 Vrms,
VBO = 65 Vrms.
Over Power Limit (NCP1239F)
Overload conditions may push the converter to draw an
excessive power (which generally increases versus the input
voltage). One must avoid such a behavior:
a) not to have to dimension the converter for a power
higher than the nominal one,
b) to meet SMPS specifications that often request the
power not to exceed a given level.
In addition, it is not recommended to provide the output
with more power than normally necessary. To the light of
these statements, it becomes interesting to accurately limit
the amount of power drawn from the AC line in fault
conditions. The easiest way to do so consists of clamping the
peak current since in a discontinuous mode flyback
converter, the input power (Pin) can be calculated as
follows: Pin = 1/2 * Lp * Ip
pk2
* fsw, where Lp is the primary
inductor, Ip
pk
is the inductor peak current and fsw is the
switching frequency.
Practically, a sense resistor converts the primary current
into a voltage that is compared to a voltage reference. When
the voltage representative of the current exceeds the voltage
reference, the controller turns off the power switch. The
theoretical maximum peak current is then: Imax =
Vocp/Rsense, where Vocp is the reference voltage (or
overcurrent protection threshold) and Rsense is the sense
resistor.
Unfortunately, the controller cannot turn off the power
switch immediately when it detects that the current exceeds
its maximum permissible level. Internal propagation delays
differ the drive turn low. In addition, the power switch needs
some time to turn off. Finally, the real current stop can be
250ns or more delayed. During this time, the current
continues ramping up so that an overcurrent is obtained.
相關(guān)PDF資料
PDF描述
NCP1239FDR2 Low−Standby High Performance PWM Controller
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NCP1239VDR2 Low−Standby High Performance PWM Controller
NCP1239VDR2G Low−Standby High Performance PWM Controller
NCP1271 Soft−Skip Mode Standby PWM Controller with Adjustable Skip Level and External Latch
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
NCP1239D 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Low-Standby High Performance PWM Controller
NCP1239F 制造商:ONSEMI 制造商全稱:ON Semiconductor 功能描述:AC-DC Offline Switching Controllers/Regulators
NCP1239FDR2 功能描述:電流型 PWM 控制器 Low Standby Power RoHS:否 制造商:Texas Instruments 開(kāi)關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14
NCP1239FDR2G 功能描述:電流型 PWM 控制器 Low Standby Power High Performance PWM RoHS:否 制造商:Texas Instruments 開(kāi)關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14
NCP1239V 制造商:ONSEMI 制造商全稱:ON Semiconductor 功能描述:AC-DC Offline Switching Controllers/Regulators
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