参数资料
型号: NCP1910GEVB
厂商: ON Semiconductor
文件页数: 21/37页
文件大小: 0K
描述: BOARD DEMO NCP1910DEMO-B-TLS
设计资源: NCP1910 Schematic
NCP1910GEVB BOM
标准包装: 1
主要目的: DC/DC,步降
输出及类型: 1,非隔离
输出电压: 最低可调至 0.8V
电流 - 输出: 3A
输入电压: 3 ~ 5.5 V
稳压器拓扑结构: 降压
频率 - 开关: 1MHz
板类型: 完全填充
已供物品:
已用 IC / 零件: NCP1910
其它名称: NCP1910GEVBOS
NCP1910
V PREF
V PREF
Figure 43. PFC Duty Modulation and Timing Diagram
V ramp + V M ) + V PREF
Z in +
I ch +
V M + V PREF * + V PREF
T (eq. 6)
The PFC modulation and timing diagram is shown in
Figure 43. The MOSFET on time t 1 is generated by the
intersection of reference voltage V PREF and ramp voltage
V ramp . A relationship in Equation 4 is obtained.
I ch t 1
(eq. 4)
C ramp
Where:
? V ramp is the internal ramp voltage, the positive input
of the PFC modulation comparator,
? V M is the multiplier voltage appearing on V M pin,
? I ch is the internal charging current,
? C ramp is the internal ramp capacitor, and
? V PREF is the internal reference voltage, the negative
input of the PFC modulation comparator.
I ch , C ramp , and V PREF also act as the ramp signal of
switching frequency. Hence the charging current I ch is
specially designed as in Equation 5. The multiplier voltage
V M is therefore expressed in terms of t 1 in Equation 6.
C ramp V PREF
(eq. 5)
T
t 1 C ramp V PREF T * t 1
C ramp T
From Equation 3 and Equation 6, the input impedance Z in
is re ? formulated in Equation 7.
V M V bulk
(eq. 7)
V PREF I L ? 50
Because V PREF and V bulk are roughly constant versus
time, the multiplier voltage V M is designed to be
proportional to the I L ? 50 in order to have a constant Z in for
PFC purpose. It is illustrated in Figure 44.
Figure 44. Multiplier Voltage Timing Diagram
It can be seen in the timing diagram in Figure 43 that V M
originally consists of a switching frequency ripple coming
from the inductor current I L . The duty ratio can be
inaccurately generated due to this ripple. This modulation is
the so ? called “peak current mode”. Hence, an external
capacitor C M connected to the multiplier voltage V M pin is
essential to bypass the high ? frequency component of V M .
The modulation becomes the so ? called “average current
mode” with a better accuracy for PFC.
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