參數(shù)資料
型號(hào)： LM2575
廠商： ON SEMICONDUCTOR
英文描述： 1.0 A, Adjustable Output Voltage, Step-Down Switching Regulator(1.0A,可調(diào)輸出電壓,降壓型開關(guān)穩(wěn)壓器)
中文描述： 1.0甲，可調(diào)輸出電壓，降壓型開關(guān)穩(wěn)壓器（1.0安培，可調(diào)輸出電壓，降壓型開關(guān)穩(wěn)壓器）
文件頁(yè)數(shù)： 20/28頁(yè)
文件大?。?/td> 363K
代理商： LM2575
LM2575
http://onsemi.com
20
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 H
Output
2
4
Feedback
Regulated
Output
V
out
= 12 V
Load Current from
200 mA for V
in
= 5.2 V
to 500 mA for V
in
= 7.0 V
Unregulated
DC Input
V
in
= 5.0 V to 12 V
L1
D1
C
out
1000 F
/16 V
C
in
100 F
/50 V
LM257512
1
5
3
ON/OFF
GND
+V
in
Design Recommendations:
The same design rules as for the previous inverting
buckboost converter can be applied. The output capacitor
C
out
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 F). 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
+V
in
+V
in
C1
0.1 F
C
in
100 F
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
V
th
≈
13 V
C
in
100 F
LM25755.0
1
3
5
GND
ON/OFF
+V
in
+V
in
NOTE: This picture does not show the complete circuit.
相關(guān)PDF資料
PDF描述
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
LM2575/D 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Easy Switcher? 1.0 A Step-Down Voltage Regulator
LM2575_05 制造商:ONSEMI 制造商全稱:ON Semiconductor 功能描述:1.0 A, Adjustable Output Voltage, Step−Down Switching Regulator
LM2575_06 制造商:TI 制造商全稱:Texas Instruments 功能描述:1-A SIMPLE STEP-DOWN SWITCHING VOLTAGE REGULATOR
LM2575_09 制造商:MICREL 制造商全稱:Micrel Semiconductor 功能描述:52kHz Simple 1A Buck Regulator
LM2575-05IKC 制造商:TI 制造商全稱:Texas Instruments 功能描述:1-A SIMPLE STEP DOWN SWITCHING VOLTAGE REGULATOR
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