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參數(shù)資料
| 型號： | LM2576-12MWC |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 7.5 A SWITCHING REGULATOR, 63 kHz SWITCHING FREQ-MAX, UUC |
| 封裝： | WAFER |
| 文件頁數(shù)： | 9/27頁 |
| 文件大小： | 741K |
| 代理商： | LM2576-12MWC |
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Additional Applications (Continued)
negative output voltage, then by grounding the feedback pin,
the regulator senses the inverted output voltage and regu-
lates it to 12V.
For an input voltage of 12V or more, the maximum available
output current in this configuration is approximately 700 mA.
At lighter loads, the minimum input voltage required drops to
approximately 4.7V.
The switch currents in this buck-boost configuration are
higher than in the standard buck-mode design, thus lowering
the available output current. Also, the start-up input current
of the buck-boost converter is higher than the standard
buck-mode regulator, and this may overload an input power
source with a current limit less than 5A. Using a delayed
turn-on or an undervoltage lockout circuit (described in the
next section) would allow the input voltage to rise to a high
enough level before the switcher would be allowed to turn
on.
Because of the structural differences between the buck and
the buck-boost regulator topologies, the buck regulator de-
sign procedure section can not be used to to select the in-
ductor or the output capacitor. The recommended range of
inductor values for the buck-boost design is between 68 H
and 220 H, and the output capacitor values must be larger
than what is normally required for buck designs. Low input
voltages or high output currents require a large value output
capacitor (in the thousands of micro Farads).
The peak inductor current, which is the same as the peak
switch current, can be calculated from the following formula:
Where f
osc = 52 kHz. Under normal continuous inductor cur-
rent operating conditions, the minimum V
IN represents the
worst case. Select an inductor that is rated for the peak cur-
rent anticipated.
Also, the maximum voltage appearing across the regulator is
the absolute sum of the input and output voltage. For a 12V
output, the maximum input voltage for the LM2576 is +28V,
or +48V for the LM2576HV.
The
Switchers Made Simple (version 3.0) design software
can be used to determine the feasibility of regulator designs
using different topologies, different input-output parameters,
different components, etc.
NEGATIVE BOOST REGULATOR
Another variation on the buck-boost topology is the negative
boost configuration. The circuit in
Figure 11 accepts an input
voltage ranging from 5V to 12V and provides a regulated
12V output. Input voltages greater than 12V will cause the
output to rise above 12V, but will not damage the regulator.
Because of the boosting function of this type of regulator, the
switch current is relatively high, especially at low input volt-
ages. Output load current limitations are a result of the maxi-
mum current rating of the switch. Also, boost regulators can
not provide current limiting load protection in the event of a
shorted load, so some other means (such as a fuse) may be
necessary.
UNDERVOLTAGE LOCKOUT
In some applications it is desirable to keep the regulator off
until the input voltage reaches a certain threshold. An under-
voltage lockout circuit which accomplishes this task is shown
in
Figure 12, while Figure 13 shows the same circuit applied
to a buck-boost configuration. These circuits keep the regu-
lator off until the input voltage reaches a predetermined
level.
V
TH ≈ VZ1 +2VBE(Q1)
DS011476-14
FIGURE 10. Inverting Buck-Boost Develops 12V
DS011476-15
Typical Load Current
400 mA for VIN = 5.2V
750 mA for VIN = 7V
Note: Heat sink may be required.
FIGURE 11. Negative Boost
DS011476-16
Note: Complete circuit not shown.
FIGURE 12. Undervoltage Lockout for Buck Circuit
www.national.com
17
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM2576-12WT | 功能描述:直流/直流開關(guān)調(diào)節(jié)器 3A Step-Down SMPS Regulator (ROHS Compliant) RoHS:否 制造商:International Rectifier 最大輸入電壓:21 V 開關(guān)頻率:1.5 MHz 輸出電壓:0.5 V to 0.86 V 輸出電流:4 A 輸出端數(shù)量: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:PQFN 4 x 5 |
| LM2576-12WU | 功能描述:直流/直流開關(guān)調(diào)節(jié)器 3A Step-Down SMPS Regulator (ROHS Compliant) RoHS:否 制造商:International Rectifier 最大輸入電壓:21 V 開關(guān)頻率:1.5 MHz 輸出電壓:0.5 V to 0.86 V 輸出電流:4 A 輸出端數(shù)量: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:PQFN 4 x 5 |
| LM2576-12WU TR | 功能描述:直流/直流開關(guān)調(diào)節(jié)器 3A Step-Down SMPS Regulator (ROHS Compliant) RoHS:否 制造商:International Rectifier 最大輸入電壓:21 V 開關(guān)頻率:1.5 MHz 輸出電壓:0.5 V to 0.86 V 輸出電流:4 A 輸出端數(shù)量: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:PQFN 4 x 5 |
| LM2576-15 | 制造商:MOTOROLA 制造商全稱:Motorola, Inc 功能描述:Easy Switcher 3.0A Step-Down Voltage Regulator |
| LM2576-15BT | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Voltage-Mode SMPS Controller |
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