Electronic Components Datasheet Search
  English  ▼

Delete All
ON OFF
ALLDATASHEET.COM

X  

Preview PDF Download HTML

LM2585 Datasheet(PDF) 20 Page - National Semiconductor (TI)

[Old version datasheet] Texas Instruments acquired National semiconductor. Click here to check the latest version.
Part No. LM2585
Description  SIMPLE SWITCHER 3A Flyback Regulator
Download  25 Pages
Scroll/Zoom Zoom In 100% Zoom Out
Maker  NSC [National Semiconductor (TI)]
Homepage  http://www.national.com
Logo NSC - National Semiconductor (TI)

LM2585 Datasheet(HTML) 20 Page - National Semiconductor (TI)

Back Button LM2585 Datasheet HTML 16Page - National Semiconductor (TI) LM2585 Datasheet HTML 17Page - National Semiconductor (TI) LM2585 Datasheet HTML 18Page - National Semiconductor (TI) LM2585 Datasheet HTML 19Page - National Semiconductor (TI) LM2585 Datasheet HTML 20Page - National Semiconductor (TI) LM2585 Datasheet HTML 21Page - National Semiconductor (TI) LM2585 Datasheet HTML 22Page - National Semiconductor (TI) LM2585 Datasheet HTML 23Page - National Semiconductor (TI) LM2585 Datasheet HTML 24Page - National Semiconductor (TI) Next Button
Zoom Inzoom in Zoom Outzoom out
 20 / 25 page
background image
Application Hints
PROGRAMMING OUTPUT VOLTAGE
(SELECTING R
1 AND R2)
Referring to the adjustable regulator in
Figure 38, the output
voltage is programmed by the resistors R
1 and R2 by the fol-
lowing formula:
V
OUT = VREF (1+R1/R2)
where V
REF = 1.23V
Resistors R
1 and R2 divide the output voltage down so that
it can be compared with the 1.23V internal reference. With
R
2 between 1k and 5k, R1 is:
R
1 = R2 (VOUT/VREF − 1)
where V
REF = 1.23V
For best temperature coefficient and stability with time, use
1% metal film resistors.
SHORT CIRCUIT CONDITION
Due to the inherent nature of boost regulators, when the out-
put is shorted (see
Figure 38), current flows directly from the
input, through the inductor and the diode, to the output, by-
passing the switch. The current limit of the switch
does not
limit the output current for the entire circuit. To protect the
load and prevent damage to the switch, the current must be
externally limited, either by the input supply or at the output
with an external current limit circuit. The external limit should
be set to the maximum switch current of the device, which is
3A.
In a flyback regulator application (
Figure 39), using the stan-
dard transformers, the LM2585 will survive a short circuit to
the main output. When the output voltage drops to 80% of its
nominal value, the frequency will drop to 25 kHz. With a
lower frequency, off times are larger. With the longer off
times, the transformer can release all of its stored energy be-
fore the switch turns back on. Hence, the switch turns on ini-
tially with zero current at its collector. In this condition, the
switch current limit will limit the peak current, saving the
device.
DS012515-55
FIGURE 38. Boost Regulator
DS012515-56
FIGURE 39. Flyback Regulator
www.national.com
20


Html Pages

1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25 


Datasheet Download

Go To PDF Page


Link URL




Privacy Policy
ALLDATASHEET.COM
Does ALLDATASHEET help your business so far?  [ DONATE ]  

About Alldatasheet   |   Advertisement   |   Datasheet Upload   |   Contact us   |   Privacy Policy   |   Alldatasheet API   |   Link Exchange   |   Manufacturer List
All Rights Reserved© Alldatasheet.com


Mirror Sites
English : Alldatasheet.com  |   English : Alldatasheet.net  |   Chinese : Alldatasheetcn.com  |   German : Alldatasheetde.com  |   Japanese : Alldatasheet.jp
Russian : Alldatasheetru.com  |   Korean : Alldatasheet.co.kr  |   Spanish : Alldatasheet.es  |   French : Alldatasheet.fr  |   Italian : Alldatasheetit.com
Portuguese : Alldatasheetpt.com  |   Polish : Alldatasheet.pl  |   Vietnamese : Alldatasheet.vn