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參數(shù)資料
| 型號(hào)： | RC4391 |
| 廠商： | Fairchild Semiconductor Corporation |
| 英文描述： | Inverting and Step-Down Switching Regulator |
| 中文描述： | 反相和降壓型開關(guān)穩(wěn)壓器 |
| 文件頁數(shù)： | 7/22頁 |
| 文件大?。?/td> | 153K |
| 代理商： | RC4391 |
RC4391
PRODUCT SPECIFICATION
7
Figure 9. Inverting Regulator Waveforms
B
A
C
D
E
F
G
1.78V
0.62V
(Internal)
I
0 mA
+V
(Internal)
+V - 0.7V
Max
0 mA
I
MAX
0 mA
+V - V
Ground
-V - V
C
O
I
V
I
I
V
X
SC
LOAD
BEQ1
LX
D
LX
L
S
S
SW
D
65-2472
BAT
L
OUT
L
X
X
V
V
This feedback system will vary the duration of the on time in
response to changes in load current or battery voltage (see
Figure 9). If the load current increases (waveform C), then
the transistor will remain on (waveform D) for a longer por-
tion of the oscillator cycle, (waveform B) to build up to a
higher peak value. The duty cycle of the switch transistor
varies in response to changes in load and line.
Step-Down Regulator
The step-down circuit function is similar to inversion; it uses
the same components (switch, inductor, diode, filter capaci-
tor), and charges and discharges the inductor by closing and
opening the switch. The great difference is that the inductor
is in series with the load; therefore, both the charging current
and the discharge current flow into the load. In the inverting
circuit only the discharge current flows into the load. Refer
to Figure 10.
When the switch S is closed, current flows from the battery,
through the inductor, and through the load resistor to ground.
After the switch is opened, stored energy in the inductor
causes current to keep flowing through the load, the circuit
being completed by the catch diode D. Since current flows to
the load during charge and discharge, the average load cur-
rent will be greater than in an inverting circuit. The signifi-
cance of that is that for equal load currents the step-down
circuit will require less peak inductor current than an invert-
ing circuit. Therefore, the inductor will not require as large
of a core, and the switch transistor will not be stressed as
heavily for equal load currents.
Figure 11 depicts a complete schematic for a step-down cir-
cuit using the RC4391. Observe that the ground lead of the
4391 is
not
connected to circuit ground; instead, it is tied to
the output voltage. It is by this rearrangement that the feed-
back system, which senses voltages more negative than the
ground lead, can be used to regulate a non-negative output
voltage.
Figure 10. Simple Step-Down Regulator
D
(+)
(-)
V
OUT
S
C
S
L
+V
65-2473
R
L
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