FAN4800CUN【PDF 16/19 页】IC PWM/PFC CTLR COMBO 16-MDIP

收藏本站

您好，
买卖IC网欢迎您。
请登录
免费注册

买卖IC网

Sheet目录38

12页 13页 14页 15页 [16页]17页 18页 19页

?2011 Fairchild Semiconductor Corporation

www.fairchildsemi.com

FAN4800AU/CU " Rev. 1.0.1

AC Line Drops Out

FAN4800AU/CU is designed such that the operation of

PFC part is not perturbed by AC line dropout. Once line

voltage disappears, the error amplifier can be saturated,

resulting in abnormal current waveforms when the line

voltage is recovered if proper preventive measures are

not employed.

With a limited gain modulator operation, FAN4800AU

/CU guarantees stable PFC operation even when AC

line is recovered from dropout, as shown in Figure 36.

I L I M

I T

( g

)

t u

r a

t i o

I L

Figure 36. AC Cycle Drop

Line Sag Protection

When the line sags below its normal operational range,

the PFC part keeps operating until the brownout

protection is triggered, which has 1 s debounce time.

Due to the low line voltage, the gain modulator for

current loop is saturated and input current of PFC is

limited, resulting in a drop of the PFC output voltage at

heavy-load condition. Since the PWM part has a V

comparator that shuts down PWM operation when the

FBPFC voltage drops below 1.3 V, the downstream

DC/DC converter can stop operation while the PFC

output voltage drops during line sag. Once the

downstream converter stops operation, even the limited

PFC input current can charge up the PFC output since

the PFC part has no load current. Because this can

cause repeated startup and shutdown of downstream

converter during line sag, FAN4800AU/CU has line sag

protection.

There are two conditions that trigger line sag protection,

as shown in Figure 37 and Figure 38. The first condition

is when V

RMS

is lower than V

RMS-SAG

(0.85 V) for longer

than t

SAG

(33 ms), as shown in Figure 37. The second

condition is when V

RMS

is lower than V

RMS-SAG

(0.85 V)

and VF

BPFC

is lower than V

IN-OFF

(1.3 V), as shown in

Figure 38. Once line sag protection is triggered, the

PWM and the PFC stop operation until V

RMS

increases

above 1.9 V.

V F

B P F C

I N

R M S

0 . 8 5 V

3 3 m s

Figure 37. The First Condition of Sag Protection

V F

B P F C

I N

R M S

0 . 8 5 V

2 5 m s

1 . 3 V

Figure 38. The Second condition of Sag Protection

发布紧急采购，3分钟左右您将得到回复。

采购需求

(若只采购一条型号，填写一行即可)

*型号	*数量	厂商	批号	封装

添加更多采购

采购需求

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

我的联系方式