參數(shù)資料
型號： LM2575D2T-005G
廠商： ON SEMICONDUCTOR
元件分類： 穩(wěn)壓器
英文描述： 3.2 A SWITCHING REGULATOR, 63 kHz SWITCHING FREQ-MAX, PSSO5
封裝： LEAD FREE, D2PK, 5 PIN
文件頁數(shù)： 14/29頁
文件大?。?/td> 408K
代理商： LM2575D2T-005G
LM2575, NCV2575
http://onsemi.com
21
If the input voltage is greater than 12 V, the output will rise
above 12 V accordingly, but will not damage the regulator.
Figure 29. Negative Boost Regulator
1N5817
150
mH
Output
2
4
Feedback
Regulated
Output
Vout = -12 V
Load Current from
200 mA for Vin = -5.2 V
to 500 mA for Vin = -7.0 V
Unregulated
DC Input
-Vin = -5.0 V to -12 V
L1
D1
Cout
1000
mF
/16 V
Cin
100
mF
/50 V
LM257512
1
5
3
ON/OFF
GND
+Vin
Design Recommendations:
The same design rules as for the previous inverting
buckboost converter can be applied. The output capacitor
Cout must be chosen larger than would be required for a
standard buck converter. Low input voltages or high output
currents require a large value output capacitor (in the range
of thousands of
mF). The recommended range of inductor
values for the negative boost regulator is the same as for
inverting converter design.
Another important point is that these negative boost
converters cannot provide current limiting load protection in
the event of a short in the output so some other means, such
as a fuse, may be necessary to provide the load protection.
Delayed Startup
There are some applications, like the inverting regulator
already mentioned above, which require a higher amount of
startup current. In such cases, if the input power source is
limited, this delayed startup feature becomes very useful.
To provide a time delay between the time the input voltage
is applied and the time when the output voltage comes up,
the circuit in Figure 30 can be used. As the input voltage is
applied, the capacitor C1 charges up, and the voltage across
the resistor R2 falls down. When the voltage on the ON/OFF
pin falls below the threshold value 1.4 V, the regulator starts
up. Resistor R1 is included to limit the maximum voltage
applied to the ON/OFF pin, reduces the power supply noise
sensitivity, and also limits the capacitor C1 discharge
current, but its use is not mandatory.
When a high 50 Hz or 60 Hz (100 Hz or 120 Hz
respectively) ripple voltage exists, a long delay time can
cause some problems by coupling the ripple into the
ON/OFF pin, the regulator could be switched periodically
on and off with the line (or double) frequency.
Figure 30. Delayed Startup Circuitry
R1
47 k
LM2575XX
1
3
5
GND
ON/OFF
R2
47 k
+Vin
C1
0.1
mF
Cin
100
mF
NOTE: This picture does not show the complete circuit.
Undervoltage Lockout
Some applications require the regulator to remain off until
the input voltage reaches a certain threshold level. Figure 31
shows an undervoltage lockout circuit applied to a buck
regulator. A version of this circuit for buckboost converter
is shown in Figure 32. Resistor R3 pulls the ON/OFF pin
high and keeps the regulator off until the input voltage
reaches a predetermined threshold level, which is
determined by the following expression:
Vth [ VZ1 ) 1 )
R2
R1
VBE (Q1)
Figure 31. Undervoltage Lockout Circuit for
Buck Converter
R2
10 k
Z1
1N5242B
R1
10 k
Q1
2N3904
R3
47 k
Vth ≈ 13 V
Cin
100
mF
LM25755.0
1
3
5
GND
ON/OFF
+Vin
NOTE: This picture does not show the complete circuit.
相關(guān)PDF資料
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LM2575HVT-ADJFLOWLB03 3.2 A SWITCHING REGULATOR, 63 kHz SWITCHING FREQ-MAX, PSFM5
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LM2575D2T-015G 功能描述:直流/直流開關(guān)調(diào)節(jié)器 15V 1A Buck PWM 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: 安裝風格:SMD/SMT 封裝 / 箱體:PQFN 4 x 5
LM2575D2T-12 制造商:MOTOROLA 制造商全稱:Motorola, Inc 功能描述:EASY SWITCHERE⑩ 1.0 A STEP-DOWN VOLTAGE REGULATOR
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