
RC4190
PRODUCT SPECIFICATION
15
The timing capacitors are set up exactly as in the voltage
dependent oscillator application of Figure 19. The values of
R2, R5, C6, and C4 that are given were chosen to optimize
for the +12V battery conditions, setting the threshold for
oscillator frequency change at V
BAT
= +8.5V.
As given, this power supply is capable of delivering +45 mA
and -15 mA with regulation, until the battery decays below
5.0V.
For information on adjusting the RC4391 to meet a specific
application refer to the Fairchild Semiconductor RC4391
data sheet.
Negative Step-Up Regulator
In the circuit of Figure 22, a bootstrap arrangement of supply
and ground pins helps generate an output voltage more nega-
tive than the input voltage. On power-up, the output filter
capacitor (C
F
) will charge through D2 and L
X
. When the
voltage goes below -2.4V, the RC4190 begins switching and
charging C
F
. The output will regulate at a value equal to the
reference voltage (1.31V) plus the zener voltage of D1. R
Z
sets the value of zener current, stabilized at 1.31V/R2.
Figure 21. RC4190/RC4391 Power Supply (
±
15V)
Figure 22. Negative Step-Up Regulator
65-2685
+V
I
C
R7
100K
LBR
4190
L2
100
μ
H
s
Cx
LBD
GND
2
3
8
Lx
V
FB
1N914
7
R3
27K
C
F2
330
μ
F
+I = 45 mA
+V
5
4
+V
LBR
4391
L1
50
μ
H
C6
40 pF
s
Cx
LBD
GND
2
3
8
Lx
V
FB
7
5
4
R5
18K
R4
100K
OUT
R2
68K
D2
C3
200 pF
1
C4
40 pF
C5
20 pF
6
R1
21M
+V
(2.4 to 5V)
6
V
+1.25V
1
C7
20 pF
C1
150
μ
F
-V
OUT
-I = -15 mA
D1
1N914
R7
100K
To +V
REF
V
+V = V (R3
-V = +V ( R7
V
I
+V
C
Gnd
3
L
65-4131
7
6
5
2
4
D1
R1
1M
R2
10K
-V
OUT
+C
F
S
X
IN
C
X
C
FB
R3
R4
Q1
L
X
D2
-V
X
4190