參數(shù)資料
型號(hào)： RC4391N
廠商： RAYTHEON SEMICONDUCTOR
元件分類(lèi)： 穩(wěn)壓器
英文描述： Inverting and Step-Down Switching Regulator
中文描述： 0.375 A SWITCHING REGULATOR, PDIP8
文件頁(yè)數(shù)： 12/22頁(yè)
文件大小： 153K
代理商： RC4391N
PRODUCT SPECIFICATION
RC4391
12
Figure 9. Inverting High Power Application
65-2478
+V
4391
s
Cx
GND
3
4
Lx
5
5
0.1
μ
F
R2
7
6
V
REF
FB
V
+V
Q2
2N33904
R4
4.7K
R1
-V
OUT
R3
750
1K
R5
2K
s
Q1
TIP116
MBR140P
Lx
Cx
C1
R6
C
F
equations and suggestions for the circuits of Figures 14 and
15 also apply to these circuits. For a certain range of load
power, the RC4193 can be used for step-sown applications.
A load range from 400mW to 2W can be sustained with
fewer components (especially when stepping down greater
than 30V) than the comparable RC4391 circuit. Refer to
Fairchild Semiconductor's RC4191/4192/4193 data sheet for
a schematic of this medium power step-down application.
Voltage Dependent Oscillator
The RC4391's ability to supply load current at low battery
voltages depends on the inductor value and the oscillator fre-
quency. Low values of inductance or a low oscillator fre-
quency will cause a higher peak inductor current and
therefore increase the load current capability. A large induc-
tor current is not necessarily best , however, because the
large amount of energy delivered with each cycle will cause
a large voltage ripple at the output, especially at high input
voltages. This trade-off between load current capability and
output ripple can be improved with the circuit connection
shown in Figure 18. This circuit uses the low battery detector
to sense for a low battery voltage condition and will
decrease the oscillator frequency after a pre- programmed
threshold is reached.
The threshold is programmed exactly as the normal low bat-
tery detector connection:
When the battery voltage reaches this threshold the compara-
tor will turn on the open collector transistor at pin 2, effec-
tively pulling C
Y
in parallel with C
X
. This added
capacitance will reduce the oscillator frequency, according to
the following equation:
Current Limiting
The oscillator (C
X
) pin can be used to add short circuit pro-
tection and to protect against over current at start-up (when
using large values for the output filter capacitor —greater
than 100
m
F). A transistor V
BE
is used as a current sensing
comparator which resets the oscillator upon sensing an over
current condition, thus providing cycle-by-cycle current lim-
iting. Figure 19 shows how this is applied.
V
TH
V
REF
R5
R4
1
+
è
=
FOHz
(
)
–
CXpF
(
)
CYpF
(
)
-----------4.1x106
=
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