参数资料
型号: LM1575J-CAD/883
厂商: NATIONAL SEMICONDUCTOR CORP
元件分类: 稳压器
英文描述: 3.2 A SWITCHING REGULATOR, 62 kHz SWITCHING FREQ-MAX, CDIP16
封装: CERDIP-16
文件页数: 11/30页
文件大小: 676K
代理商: LM1575J-CAD/883
Additional Applications (Continued)
UNDERVOLTAGE LOCKOUT
In some applications it is desirable to keep the regulator off
until the input voltage reaches a certain threshold. An under-
voltage lockout circuit which accomplishes this task is shown
in
Figure 12, while Figure 13 shows the same circuit applied
to a buck-boost configuration. These circuits keep the regu-
lator off until the input voltage reaches a predetermined
level.
V
TH ≈ VZ1 +2VBE (Q1)
DELAYED STARTUP
The ON /OFF pin can be used to provide a delayed startup
feature as shown in
Figure 14. With an input voltage of 20V
and for the part values shown, the circuit provides approxi-
mately 10 ms of delay time before the circuit begins switch-
ing. Increasing the RC time constant can provide longer de-
lay times. But excessively large RC time constants can
cause problems with input voltages that are high in 60 Hz or
120 Hz ripple, by coupling the ripple into the ON /OFF pin.
ADJUSTABLE OUTPUT, LOW-RIPPLE
POWER SUPPLY
A 1A power supply that features an adjustable output voltage
is shown in
Figure 15. An additional L-C filter that reduces
the output ripple by a factor of 10 or more is included in this
circuit.
DS011475-16
Typical Load Current
200 mA for VIN = 5.2V
500 mA for VIN = 7V
Note: Pin numbers are for TO-220 package.
FIGURE 11. Negative Boost
DS011475-17
Note: Complete circuit not shown.
Note: Pin numbers are for the TO-220 package.
FIGURE 12. Undervoltage Lockout for Buck Circuit
DS011475-18
Note: Complete circuit not shown (see
Figure 10).
Note: Pin numbers are for the TO-220 package.
FIGURE 13. Undervoltage Lockout
for Buck-Boost Circuit
DS011475-19
Note: Complete circuit not shown.
Note: Pin numbers are for the TO-220 package.
FIGURE 14. Delayed Startup
www.national.com
19
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