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參數(shù)資料
| 型號(hào)： | LM78L00 |
| 廠商： | National Semiconductor Corporation |
| 元件分類： | 基準(zhǔn)電壓源/電流源 |
| 英文描述： | 5.0 AMP POSITIVE VOLTAGE REGULATOR |
| 中文描述： | 5.0放大器正電壓穩(wěn)壓器 |
| 文件頁數(shù)： | 8/10頁 |
| 文件大小： | 164K |
| 代理商： | LM78L00 |
Methods of Heat Sinking
(Continued)
The best analogy for PC board copper is to compare it with
parallel resistors. Beyond some point, additional resistors
are not significantly effective; beyond some point, additional
copper area is not effective.
TL/H/10051–5
FIGURE 2. TO-92 Thermal Equivalent Circuit
(Lead at other than Ambient Temperature)
High Dissipation Applications
TL/H/10051–6
TL/H/10051–7
Where it is necessary to operate a LM78L00 regulator with a
large input/output differential voltage, the addition of series
resistor R1 will extend the output current range of the de-
vice by sharing the total power dissipation between R1 and
the regulator.
R1
e
V
I Min
b
V
O
b
2.0V
I
L Max
a
I
Q
(2)
where:
I
Q
is the regulator quiescent current.
Regulator power dissipation at maximum input voltage and
maximum load current is now
P
D Max
e
(V
1
b
V
O
) I
L Max
a
V
1
I
Q
where:
V
1
e
V
I Max
b
(I
L Max
a
I
Q
) R1
The presence of R1 will affect load regulation according to
the equation:
(3)
Load regulation (at constant V
I
)
e
load regulation (at constant V
1
)
a
line regulation (mV per V)
c
(RI)
c
(
D
I
L
).
As an example, consider a 15V regulator with a supply volt-
age of 30
g
5.0V, required to supply a maximum load cur-
rent of 30 mA. I
Q
is 4.3 mA, and minimum load current is to
be 10 mA.
(4)
R1
e
25
b
15
b
2
30
a
4.3
e
8
34.3
j
240
X
(5)
V
1
e
35
b
(30
a
4.3) 0.24
e
35
b
8.2
e
26.8V
P
D Max
e
(26.8
b
15) 30
a
26.8 (4.3)
e
354
a
115
e
470 mW, which permit operation up to
70
§
C in most applications.
Line regulation of this circuit is typically 110 mV for an input
range of 25V–35V at a constant load current; i.e. 11 mV/V.
Load regulation
e
constant V
1
load regulation
(typically 10 mV, 10 mA–30 mA I
L
)
a
(11 mV/V)
c
0.24
c
20 mA
(typically 53 mV)
e
63 mV for a load current change of
20 mA at a constant V
I
of 30V.
(6)
Typical Applications
TL/H/10051–8
Note 1:
To specify an output voltage, substitute voltage value for ‘‘00’’.
Note 2:
Bypass capacitors are recommended for optimum stability and tran-
sient response and should be located as close as possible to the regulator.
8
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