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NCP1O1X系列的短路保护原理

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  • 2019-9-11 23:11:46
10问答币
看了多遍Datasheet 对NCP101X系列的短路保护原理一直没搞明白,下图是其内部框图(郁闷,不能贴图)

短路保护的描述如下

Short Circuit Protection
The internal protection circuitry involves a patented
arrangement that permanently monitors the assertion of an
internal error flag. This error flag is, in fact, a signal that
instructs the controller that the internal maximum peak
current limit is reached. This naturally occurs during the
startup period (Vout is not stabilized to the target value) or
when the optocoupler LED is no longer biased, e.g. in a
short−circuit condition or when the feedback network is
broken. When the DSS normally operates, the logic checks
for the presence of the error flag every time VCC crosses
VCCON. If the error flag is low (peak limit not active) then
the IC works normally. If the error signal is active, then the
NCP101X immediately stops the output pulses, reduces its
internal current consumption and does not allow the startup
source to activate: VCC drops toward ground until it reaches
the so−called latch−off level, where the current source
activates again to attempt a new restart. When the error is
gone, the IC automatically resumes its operation. If the
default is still there, the IC pulses during 8.5 V down to 7.5 V
and enters a new latch−off phase. The resulting burst
operation guarantees a low average power dissipation and
lets the SMPS sustain a permanent short−circuit. Figure 15
shows the corresponding diagram.


我的疑惑是: If the error flag is low (peak limit not active) 这一句
flag 如果是低电平,则肯定这两个三极管导通,推断出这个稳压管也是导通了的,这跟 peak limit 是否激活有什么关系的呢?是怎么判断出 峰值限制是否激活了呢?

NCP1012.pdf

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