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參數(shù)資料
| 型號： | FAN7554 |
| 廠商： | FAIRCHILD SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Versatile PWM Controller |
| 中文描述： | 1 A SWITCHING CONTROLLER, 500 kHz SWITCHING FREQ-MAX, PDIP8 |
| 封裝： | DIP-8 |
| 文件頁數(shù)： | 13/22頁 |
| 文件大小： | 1006K |
| 代理商： | FAN7554 |
FAN7554
13
Protection Circuits
The FAN7554 has many built-in protection circuits that do not need additional components, providing reliability without cost
increase. These protection circuits have the auto-restart configuration. In this configuration, the protection circuits reset when
Vcc is below UVLO stop threshold (9V) and restarts when Vcc is above UVLO start threshold voltage (15V)
Over Voltage Protection
Abnormalities may occur in the SMPS secondary side feedback circuit. First, when the feedback pin is short to the ground, the
feedback voltage is zero and the FAN7554 is unable to start switching. Second, when the feedback circuit is open, the
secondary voltage generally becomes much greater than the rated voltage as the primary side continues to switch at the
maximum current level. This may cause the blowing off the fuse or, in serious cases, fires. It is possible that the devices
directly connected to the secondary output without a regulator could be destroyed. Even in these cases, the over voltage
protection circuit operates. Since Vcc is proportional to the output , in an over voltage situation, it also will increase. In the
FAN7554, the protection circuit operates when Vcc exceeds 34V. Therefore ,in normal operation, Vcc must be set below 34V.
Over Load Protection
An overload is the state in which the load is operating normally but in excess of the preset load. The overload protection circuit
can force the FAN7554 to stop its operation . The protection can also operate in transient states such as initial SMPS operation.
Because the transient state returns to the normal state after a fixed time, the protection circuit need not to operate during this
time. That is, the FAN7554 needs the time to detect and decide whether it is an overload condition or not. The protection
circuit can be prevented from operating during transient states by ensuring that a certain amount of time passes before the
protection circuit operates. The above operations are executed as follows: Since the FAN7554 adopts a current mode, it is
impossible for current to flow above a maximum level. For a fixed input voltage, this limits power. Therefore, if the power at
the output exceeds this maximum, Vo, shown in figure21, becomes less than the set voltage, and the KA431pulls in only the
given minimum current. As a result, the photo-coupler’s secondary side current becomes zero. The same goes for the
photo-coupler’s primary side current. Consequently, when the full current 1mA flows through the internal resistor
(2R + R = 3R), Vfb becomes approximately 3V and from that time, the 5uA current source begins to charge Cfb, the
photo-coupler’s secondary current is almost zero. The FAN7554 shuts down when Vfb reaches 6V.
Figure 21. Delayed Shutdown
Q
R
UVLO out
6V
FB
Vcc
5V
5uA
1mA
R
Cfb
S
1
Vo
Vfb
KA431
FAN7554
2R
Q
R
S
OSC
Shutdown
t
V
5uA = (Cfb *3V)/t2
Time Constant = 3R * Cfb
3V
6V
Shutdown start point
t2
t1
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| FAN7554_03 | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:Versatile PWM Controller |
| FAN7554D | 功能描述:DC/DC 開關(guān)控制器 PWM Controller RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| FAN7554D_Q | 功能描述:電流型 PWM 控制器 PWM Controller RoHS:否 制造商:Texas Instruments 開關(guān)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(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
| FAN7554DTF | 功能描述:DC/DC 開關(guān)控制器 PWM Controller RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| FAN7554DTF_Q | 功能描述:電流型 PWM 控制器 PWM Controller RoHS:否 制造商:Texas Instruments 開關(guān)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(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
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