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參數(shù)資料
| 型號： | LM7800C |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Series 3-Terminal Positive Regulators |
| 中文描述： | 系列三端穩(wěn)壓器正 |
| 文件頁數(shù)： | 8/15頁 |
| 文件大?。?/td> | 512K |
| 代理商： | LM7800C |
Application Hints
(Continued)
the output high can cause damage to internal low current
paths in a manner similar to that just described in the “Short-
ing the Regulator Input” section.
Regulator Floating Ground
(Figure 2): When the ground
pin alone becomes disconnected, the output approaches the
unregulated input, causing possible damage to other circuits
connected to V
. If ground is reconnected with power
“ON”, damage may also occur to the regulator. This fault is
most likely to occur when plugging in regulators or modules
with on card regulators into powered up sockets. Power
should be turned off first, thermal limit ceases operating, or
ground should be connected first if power must be left on.
Transient Voltages:
If transients exceed the maximum
rated input voltage of the device, or reach more than 0.8V
below ground and have sufficient energy, they will damage
the regulator. The solution is to use a large input capacitor, a
series input breakdown diode, a choke, a transient suppres-
sor or a combination of these.
When a value for
θ
is found using the equation shown,
a heatsink must be selected that has a value that is less than
or equal to this number.
θ
is specified numerically by the heatsink manufacturer
in this catalog, or shown in a curve that plots temperature
rise vs power dissipation for the heatsink.
HEATSINKING TO-263 AND SOT-223 PACKAGE PARTS
Both the TO-263 (“S”) and SOT-223 (“MP”) packages use a
copper plane on the PCB and the PCB itself as a heatsink.
To optimize the heat sinking ability of the plane and PCB,
solder the tab of the plane.
shows for the TO-263 the measured values of
θ
for dif-
ferent copper area sizes using a typical PCB with 1 ounce
copper and no solder mask over the copper area used for
heatsinking
As shown in the figure, increasing the copper area beyond 1
square inch produces very little improvement. It should also
be observed that the minimum value of
θ
(J–A)
for the TO-263
package mounted to a PCB is 32C/W.
As a design aid, Figure 5 shows the maximum allowable
power dissipation compared to ambient temperature for the
TO-263 device (assuming
θ
is 35C/W and the maxi-
mum junction temperature is 125C).
DS007781-8
FIGURE 1. Input Short
DS007781-9
FIGURE 2. Regulator Floating Ground
DS007781-10
FIGURE 3. Transients
DS007781-39
FIGURE 4.
θ
vs Copper (1 ounce)
Area for the TO-263 Package
DS007781-40
FIGURE 5. Maximum Power Dissipation vs
T
AMB
for the TO-263 Package
www.national.com
8
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| LM7805A-220M | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Voltage Regulator |
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