參數(shù)資料
型號(hào)： LM2577TADJFLOWLB03
廠商： NATIONAL SEMICONDUCTOR CORP
元件分類： 穩(wěn)壓器
英文描述： 6 A SWITCHING REGULATOR, 62 kHz SWITCHING FREQ-MAX, PZFM5
封裝： PLASTIC, TO-220, 5 PIN
文件頁(yè)數(shù)： 5/27頁(yè)
文件大小： 889K
代理商： LM2577TADJFLOWLB03
Application Hints (Continued)
STEP-UP (BOOST) REGULATOR
Figure 4 shows the LM1577-ADJ/LM2577-ADJ used as a
Step-Up Regulator. This is a switching regulator used for
producing an output voltage greater than the input supply
voltage.
The
LM1577-12/LM2577-12
and
LM1577-15/
LM2577-15 can also be used for step-up regulators with 12V
or 15V outputs (respectively), by tying the feedback pin di-
rectly to the regulator output.
A basic explanation of how it works is as follows. The
LM1577/LM2577 turns its output switch on and off at a fre-
quency of 52 kHz, and this creates energy in the inductor (L).
When the NPN switch turns on, the inductor current charges
up at a rate of V
IN/L, storing current in the inductor. When the
switch turns off, the lower end of the inductor flies above V
IN,
discharging its current through diode (D) into the output ca-
pacitor (C
OUT) at a rate of (VOUT VIN)/L. Thus, energy
stored in the inductor during the switch on time is transferred
to the output during the switch off time. The output voltage is
controlled by the amount of energy transferred which, in turn,
is controlled by modulating the peak inductor current. This is
done by feeding back a portion of the output voltage to the
error amp, which amplifies the difference between the feed-
back voltage and a 1.230V reference. The error amp output
voltage is compared to a voltage proportional to the switch
current (i.e., inductor current during the switch on time).
The comparator terminates the switch on time when the two
voltages are equal, thereby controlling the peak switch cur-
rent to maintain a constant output voltage.
Voltage and current waveforms for this circuit are shown in
Figure 5, and formulas for calculating them are given in Fig-
ure 6.
STEP-UP REGULATOR DESIGN PROCEDURE
The following design procedure can be used to select the ap-
propriate external components for the circuit in
Figure 4,
based on these system requirements.
Given:
V
IN (min) = Minimum input supply voltage
V
OUT = Regulated output voltage
I
LOAD(max) = Maximum output load current
Before proceeding any further, determine if the LM1577/
LM2577 can provide these values of V
OUT and ILOAD(max)
when operating with the minimum value of V
IN. The upper
limits for V
OUT and ILOAD(max) are given by the following
equations.
V
OUT ≤ 60V
and
V
OUT ≤ 10xVIN(min)
These limits must be greater than or equal to the values
specified in this application.
1. Inductor Selection (L)
A.
Voltage Options:
1. For 12V or 15V output
DS011468-11
FIGURE 5. Step-Up Regulator Waveforms
Duty Cycle
D
Average
Inductor
Current
I
IND(AVE)
Inductor
Current
Ripple
I
IND
Peak
Inductor
Current
I
IND(PK)
Peak Switch
Current
I
SW(PK)
Switch
Voltage
When Off
V
SW(OFF)
V
OUT +VF
Diode
Reverse
Voltage
V
R
V
OUT VSAT
Average
Diode
Current
I
D(AVE)
I
LOAD
Peak Diode
Current
I
D(PK)
Power
Dissipation
of
LM1577/2577
P
D
VF = Forward Biased Diode Voltage
ILOAD = Output Load Current
FIGURE 6. Step-Up Regulator Formulas
www.national.com
13
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
LM2577T-ADJFLOWLB03 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Current-Mode SMPS Controller
LM2578AM 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT
LM2578AM/NOPB 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT
LM2578AM/NOPB 制造商:Texas Instruments 功能描述:DC/DC Converter IC
LM2578AMX 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT
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