LM2577S-12/NOPB National Semiconductor, LM2577S-12/NOPB Datasheet - Page 21
![IC REG SIMPLE SWITCHER TO-263-5](/photos/7/0/70012/ts5b_sml.jpg)
LM2577S-12/NOPB
Manufacturer Part Number
LM2577S-12/NOPB
Description
IC REG SIMPLE SWITCHER TO-263-5
Manufacturer
National Semiconductor
Series
SIMPLE SWITCHER®r
Type
Step-Up (Boost), Flyback, Forward Converterr
Datasheet
1.LM2577T-15NOPB.pdf
(31 pages)
Specifications of LM2577S-12/NOPB
Internal Switch(s)
Yes
Synchronous Rectifier
No
Number Of Outputs
1
Voltage - Output
12V
Current - Output
3A
Frequency - Switching
52kHz
Voltage - Input
3.5 ~ 40 V
Operating Temperature
-40°C ~ 125°C
Mounting Type
Surface Mount
Package / Case
D²Pak, TO-263 (5 leads + tab)
Input Voltage
40V
Output Voltage
15V
No. Of Pins
5
Operating Temperature Range
-40°C To +125°C
Msl
MSL 3 - 168 Hours
Switching Frequency Max
52kHz
Termination Type
SMD
Voltage Regulator Type
Boost Switching
Rohs Compliant
Yes
Filter Terminals
SMD
Input Voltage Primary Max
40V
Output Current Max
3A
For Use With
551011367-061 - BOARD WEBENCH LM2577,LM2585/87
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Power - Output
-
Other names
*LM2577S-12
*LM2577S-12/NOPB
LM2577S-12
*LM2577S-12/NOPB
LM2577S-12
Application Hints
FLYBACK REGULATOR
A Flyback regulator can produce single or multiple output
voltages that are lower or greater than the input supply
voltage. Figure 18 shows the LM1577/LM2577 used as a
flyback regulator with positive and negative regulated out-
puts. Its operation is similar to a step-up regulator, except the
output switch contols the primary current of a flyback trans-
former. Note that the primary and secondary windings are
out of phase, so no current flows through secondary when
current flows through the primary. This allows the primary to
charge up the transformer core when the switch is on. When
the switch turns off, the core discharges by sending current
through the secondary, and this produces voltage at the
outputs. The output voltages are controlled by adjusting the
peak primary current, as described in the step-up regulator
section.
Voltage and current waveforms for this circuit are shown in
Figure 17, and formulas for calculating them are given in
Figure 19.
FLYBACK REGULATOR DESIGN PROCEDURE
1. Transformer Selection
A family of standardized flyback transformers is available for
creating flyback regulators that produce dual output volt-
ages, from
20lists these transformers with the input voltage, output
voltages and maximum load current they are designed for.
2. Compensation Network (C
Output Capacitor (C
As explained in the Step-Up Regulator Design Procedure,
C
procedure is for a dual output flyback regulator with equal
turns ratios for each secondary (i.e., both output voltages
have the same magnitude). The equations can be used for a
single output regulator by changing
in the following equations.
C
, R
C
and C
±
OUT
10V to
must be selected as a group. The following
±
OUT
15V, as shown in Figure 18. Figure
) Selection
C
(Continued)
, R
C
∑
) and
I
LOAD(max)
to I
LOAD(max)
21
A. First, calculate the maximum value for R
Where
tude) required from both outputs. Select a resistor less than
or equal to this value, and no greater than 3 kΩ.
B. Calculate the minimum value for
at both outputs) using the following two equations.
The larger of these two values must be used to ensure
regulator stability.
FIGURE 17. Flyback Regulator Waveforms
∑
I
LOAD(max)
is the sum of the load current (magni-
∑
C
OUT
01146817
(sum of C
C
.
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OUT