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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)： | 6/22頁 |
| 文件大?。?/td> | 153K |
| 代理商： | RC4391 |
PRODUCT SPECIFICATION
RC4391
6
Principles of Operation
The basic switching inverter circuit is the building block on
which the complete inverting application is based.
A simplified diagram of the voltage inverter circuit with
ideal components and no feedback circuitry is shown in
Figure 7. When the switch S is closed, charging current from
the battery flows through the inductor L, which builds up a
magnetic field, increasing as the switch is held closed. When
the switch is opened, the magnetic field collapses, and the
energy stored in the magnetic field is converted into a current
which flows through the inductor in the same direction as the
changing current. Because there is no path for this current to
flow through the switch, the current must flow through the
diode to charge the capacitor C. The key to the inversion is
the ability of the inductor to become a source when the
charging current is removed.
The equation V = L (di/dt) gives the maximum possible
voltage across the inductor; in the actual application, feed-
back circuitry and the output capacitor will decrease the
output voltage to a regulated fixed value.
A complete schematic for the standard inverting application
is shown in Figure 8. The ideal switch in the simplified
diagram is replaced by the PNP transistor switch between
pins 5 and 6. C
F
functions as the output filter capacitor, and
D1 and L
X
replace D and L.
When power is first applied, the ground sensing comparator
(pin 8) compares the output voltage to the +1.25V voltage
reference. Because C
F
is initially discharged a positive
voltage is applied to the comparator, and the output of the
comparator gates the squarewave oscillator. This gated
squarewave signal turns on, then off, the PNP output transis-
tor. This turning on and off of the output transistor performs
the same function as opening and closing the ideal switch in
the simplified diagram; i.e., it stores energy in the inductor
during the on time and releases it into the capacitor during
the off time.
The comparator will continue to allow the oscillator to turn
the switch transistor on and off until enough energy has been
stored in the output capacitor to make the comparator input
voltage decrease to less than 0V. The voltage applied to the
comparator is set by the output voltage, the reference volt-
age, and the ratio of R1 to R2.
Figure 7. Simple Inverting Regulator
D
(+)
(–)
V
OUT
C
S
L
+V
S
65-1601
*Caution: Use current limiting protection circuit for high values of C
F
(Figure 13)
Figure 8. Inverting Regulator – Standard Circuit
C2
C1
OSC
+1.25V
REF/Bias
RC4391
65-1602
REF
V
Q1
Q2
Cx
A
To
+V
LBD
Output
R3
260K
R4
590K
R6
100K
B
C *
33
μ
F
F
R1
R2
+Vs
V
OUT
-
1N914
F
E
Lx
C1
0.1
μ
F
D1
Parts
List
R1 =
R2 =
Cx
Lx
-5.0V
Output
300 k
75 k
150 pF
1.0 mH Dale TE3 Q4 TA
-15V
Output
900 k
75 k
150 pF
= Optional
-V = (1.25V) ( R2
W
W
W
W
D
LBR
GND
C
X
LBD
L
X
+V
S
V
REF
V
FB
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