参数资料
型号: LM2577MX-12/NOPB
厂商: NATIONAL SEMICONDUCTOR CORP
元件分类: 稳压器
英文描述: 6 A SWITCHING REGULATOR, 62 kHz SWITCHING FREQ-MAX, PDSO24
封装: 0.300 INCH, SO-24
文件页数: 13/34页
文件大小: 1008K
代理商: LM2577MX-12/NOPB
Application Hints (Continued)
C.
Calculate the minimum value of CC
D.
Calculate the maximum ESR of the +V
OUT and VOUT
output capacitors in parallel.
This formula can also be used to calculate the maximum
ESR of a single output regulator.
At this point, refer to this same section in the Step-Up Regu-
lator Design Procedurefor more information regarding the
selection of C
OUT.
3. Output Voltage Selection
This section is for applications using the LM1577-ADJ/
LM2577-ADJ. Skip this section if the LM1577-12/LM2577-12
or LM1577-15/LM2577-15 is being used.
With the LM1577-ADJ/LM2577-ADJ, the output voltage is
given by
V
OUT = 1.23V (1 + R1/R2)
Resistors R1 and R2 divide the output voltage down so it can
be compared with the LM1577-ADJ/LM2577-ADJ internal
1.23V reference. For a desired output voltage V
OUT, select
R1 and R2 so that
4. Diode Selection
The switching diode in a flyback converter must withstand
the reverse voltage specified by the following equation.
A suitable diode must have a reverse voltage rating greater
than this. In addition it must be rated for more than the aver-
age and peak diode currents listed in
Figure 19.
5. Input Capacitor Selection
The primary of a flyback transformer draws discontinuous
pulses of current from the input supply. As a result, a flyback
regulator generates more noise at the input supply than a
step-up regulator, and this requires a larger bypass capacitor
to decouple the LM1577/LM2577 V
IN pin from this noise. For
most applications, a low ESR, 1.0 F cap will be sufficient, if
it is connected very close to the V
IN and Ground pins.
Duty Cycle
D
Primary Current Variation
I
P
Peak Primary Current
I
P(PK)
Switch Voltage when Off
V
SW(OFF)
Diode Reverse Voltage
V
R
V
OUT
+ N(V
IN
V
SAT)
Average Diode Current
I
D(AVE)
I
LOAD
Peak Diode Current
I
D(PK)
Short Circuit Diode Current
Power Dissipation of
LM1577/LM2577
P
D
DS011468-78
FIGURE 19. Flyback Regulator Formulas
www.national.com
20
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相关代理商/技术参数
参数描述
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LM2577N-15 制造商:NSC 制造商全称:National Semiconductor 功能描述:SIMPLE SWITCHER-R Step-Up Voltage Regulator