CMOS Micropower Step-Up
Switching Regulator
Note that this circuit (with or without the MAX8212) can be
output from a 9V battery. The reference for the -15V
output is derived from the positive output through R3
and R4. Both regulators are set to maximize output
power at low-battery voltage by reducing the oscillator
used to provide 5V from four alkaline cells. The initial volt-
age is approximately 6V, and the output is maintained at
5V even when the battery voltage falls to less than 2V.
frequency, through LBR, when V
falls to 7.2V.
BATT
Dual-Tracking Regulator
A MAX634 inverting regulator is combined with a
MAX630 in Figure 8 to provide a dual-tracking 15V
LINE-POWERED
+5V INPUT
1N4148
L
470μH
X
UNINTERRUPTABLE
+5V OUTPUT
+5V OUT
1N4001
1N5817
470μH
3
3V
470μF
15V
L
X
470μF
15V
1N5817
680Ω
3
R3
249kΩ
5
6
7
MAX630 +V
L
S
X
1
LBR
200kΩ
R
1
5
6
7
I
3.6V
NICAD
BATTERY
C
+V
MAX630
S
540kΩ
1
8
R4
499kΩ
LBR
LBD
V
FB
280kΩ
100kΩ
I
C
100kΩ
R
2
200kΩ
LBD
8
C
GND
4
X
2
V
FB
C1
100pF
GND
4
C
X
2
C
47pF
X
47pF
POWER FAIL
Figure 5. 3V to 5V Converter with Low-Battery Frequency Shift
Figure 6. Uninterruptable +5V Supply
1.0mH
9V
BATTERY
470μF
25V
1MΩ
3
5
S
2.4MΩ
8
L
+V
X
1.3MΩ
1MΩ
2MΩ
6
7
I
MAX8212
C
10MΩ
2
3
MAX630
HYST
OUT
1
V
LBR
FB
THRESHOLD
390kΩ
560kΩ
LBD
8
C
GND
4
X
2
GND
5
100pF
47pF
Figure 7. Battery Life Extension Down to 3V In
______________________________________________________________________________________ 11
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
