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参数资料
| 型号： | NCP1252BDR2G |
| 厂商： | ON Semiconductor |
| 文件页数： | 13/18页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR FLYBK ISO PWM 8SOIC |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 500kHz |
| 占空比： | 84% |
| 电源电压： | 9 V ~ 28 V |
| 降压： | 无 |
| 升压： | 无 |
| 回扫： | 是 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 是 |
| 工作温度： | -25°C ~ 125°C |
| 封装/外壳： | 8-SOIC（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
NCP1252
The following figure illustrates a soft start sequence.
Soft Start pin
T SS = 13 ms
(2 V/div)
V SS = 4 V
CS pin
(0.5 V/div)
Time
(4 ms/div)
Figure 33. Soft Start Example
Brown ? Out Protection
By monitoring the level on BO pin, the controller protects
the forward converter against low input voltage conditions.
When the BO pin level falls below the V BO level, the
controllers stops pulsing until the input level goes back to
normal and resumes the operation via a new soft start sequence.
The brown ? out comparator features a fixed voltage
reference level (V BO ). The hysteresis is implemented by
using the internal current connected between the BO pin and
the ground when the BO pin is below the internal voltage
reference (V BO ).
Vbulk
S
Q
Q
RB O u p
BO
BOK
R
shutdown
RB Olo
VBO
UVLO r eset
Grand
Reset
IBO
Figure 34. BO Pin Setup
V BO
V bulkON + R BOup I BO ) ) V BO
R BOlo
V BO +
V bulkoff R BOlo
R BOlo ) R BOup
V bulkoff * V BO
R BOup + R BOlo
V BO
The following equations show how to calculate the
resistors for BO pin.
First of all, select the bulk voltage value at which the
controller must start switching (V bulkon ) and the bulk
voltage for shutdown (V bulkoff ) the controller.
Where:
? V bulkon = 370 V
? V bulkoff = 350 V
? V BO = 1 V
? I BO = 10 m A
When BO pin voltage is below V BO (internal voltage
reference), the internal current source (I BO ) is activated. The
following equation can be written:
(eq. 1)
When BO pin voltage is higher than V BO , the internal
current source is now disabled. The following equation can
be written:
(eq. 2)
From Equation 2 it can be extracted the R BOup :
(eq. 3)
Equation 3 is substituted in Equation 1 and solved for
R BOlo , yields:
http://onsemi.com
13
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