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參數資料
| 型號： | FS7M0680YDTU |
| 廠商： | FAIRCHILD SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Fairchild Power Switch(FPS) |
| 中文描述： | 24 A SWITCHING REGULATOR, PZFM5 |
| 封裝： | TO-3P, 5 PIN |
| 文件頁數： | 6/16頁 |
| 文件大?。?/td> | 1598K |
| 代理商： | FS7M0680YDTU |
FS7M0680
6
Pulse by pulse current limit
Figure 3 shows the pulse-width-modulation (PWM) block of
the FPS. Since the FPS employs the peak current mode con-
trol, the current through the power MOSFET is limited by
the inverting input voltage of PWM comparator (Vfb*).
Assuming that the 0.9mA current source flows only through
the internal resistor (2.5R + R
·
= 2.8k) and the diode forward
voltage drop is 0.7V, the anode voltage of diode D2 is about
3.2V. Since D1 is blocked when the feedback voltage (Vfb)
exceeds 3.2V, the maximum voltage of the anode of D2 is
3.2V. Therefore, the maximum value of Vfb* is about 0.7V,
which determines the maximum current through the power
MOSFET.
Over Load Protection
Overload means that the load current exceeds a pre-set level
due to the abnormal situation. In this situation, protection
circuit should be activated in order to protect the SMPS.
However, even when the SMPS is in the normal operation,
the over load protection circuit can be activated during the
load transition. In order to avoid this undesired operation, the
over load situation should be distinguished from the normal
load transition situation. As a measure against this problem,
over load protection circuit in the FPS is designed to be acti-
vated after a specified period to determine whether it is a
transient situation or an overload situation. The protection
circuit is allowed to shut down the SMPS only when the over
load condition continues longer than preset period. The
detailed operation principle is explained in figure 3. Because
of the pulse by pulse current limit circuit, the maximum cur-
rent through the FPS is limited, and therefore the maximum
input power is restricted with a given input voltage. If the
output consumes beyond this maximum power, the output
voltage (Vo) decreases below the set voltage. This reduces
the current through the opto-coupler diode, which also
reduces opto-coupler transistor current increasing Vfb. If
Vfb exceeds 3.2V, D1 is blocked and the 5
μ
A current source
starts to charge Cfb slowly compared to when the 0.9mA
current source charges Cfb. Vfb continues increasing until it
reaches 7.5V, and the FPS shuts down at that time. The delay
time for shutdown is the time required to charge Cfb from
3.2V to 7.5V with 5
μ
A. When Cfb is 10nF (103), t2 is
approximately 8.6mS and when Cfb is 0.1
μ
F (104), t2 is
approximately 86ms. These values are enough to prevent
SMPS from being shut down for most transient situations.
Just increasing Cfb to obtain a longer delay time may cause
problems, because Cfb is an important parameter for deter-
mining the response speed of the SMPS. To solve this prob-
lem, auxiliary capacitor in series with zener diode can be
used in parallel with Cfb. The breakdown voltage of the
zener diode should be about 3.9 ~ 4.7V. When Vfb is below
the zener voltage, the system dynamics is determined by
Cfb. When Vfb exceeds the zener voltage, the delay time is
determined by the auxiliary capacitor. By using large auxil-
iary capacitor, the delay time can be extended without sacri-
fice of the dynamic response.
Over voltage Protection (OVP) Circuit
The FPS has a self-protection feature against malfunctions,
such as feedback circuit open or short-circuit. When the
feedback terminal is open due to a malfunction in the sec-
ondary side feedback circuit or a defect of solder, the current
through the opto-coupler transistor becomes almost zero.
Figure 3. Pulse-width-modulation (PWM) block
.
7.5V
3.2 V
0
t
t2
Shutdown
R
S
Q
Rsense
2.5 R
R
OSC.
Ioffset
0.9mA
5uA
Vck
Vfb
Vfb*
Sense
Q
R
S
Reset
Thermal
Shutdown
7.5V
Cfb
Shutdown
Vo
#4
FPS
KA431
D1
D2
PWM comp
A
V
C
t
fb
μ
5
3
2
×
=
相關PDF資料 |
PDF描述 |
|---|---|
| FS7M0880 | Fairchild Power Switch(FPS) |
| FS7M0880TU | Fairchild Power Switch(FPS) |
| FS7M0880YDTU | Fairchild Power Switch(FPS) |
| FS7SM-12 | HIGH-SPEED SWITCHING USE |
| FS7SM-16 | HIGH-SPEED SWITCHING USE |
相關代理商/技術參數 |
參數描述 |
|---|---|
| FS7M0880 | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:Fairchild Power Switch(FPS) |
| FS7M0880TU | 功能描述:電流型 PWM 控制器 8a/800V Power Switch 70kHz RoHS:否 制造商:Texas Instruments 開關頻率:27 KHz 上升時間: 下降時間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數量:1 最大工作溫度:+ 105 C 安裝風格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
| FS7M0880TU | 制造商:Fairchild Semiconductor Corporation 功能描述:Power Supply IC |
| FS7M0880YDTU | 功能描述:電流型 PWM 控制器 8a/800V Power Switch 70kHz RoHS:否 制造商:Texas Instruments 開關頻率:27 KHz 上升時間: 下降時間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數量:1 最大工作溫度:+ 105 C 安裝風格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
| FS7SM12 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:TRANSISTOR | MOSFET | N-CHANNEL | 600V V(BR)DSS | 7A I(D) | TO-247VAR |
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