CMOS Micropower Step-Up
Switching Regulator
Note that this circuit (with or without the MAX8212) can be
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.
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
frequency, through LBR, when V
BATT
falls to 7.2V.
MAX630/MAX4193
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
L
X
470μH
3V
R3
249kΩ
1
R4
499kΩ
LBD
8
C1
100pF
C
X
47pF
C
X
2
LBR
3
L
X
1N4148
+5V OUT
470μF
15V
1N5817
680Ω
5
6
7
R
2
200kΩ
R
1
540kΩ
200kΩ
1
100kΩ
3
L
X
3.6V
NICAD
BATTERY
1N4001
470μH
1N5817
UNINTERRUPTABLE
+5V OUTPUT
470μF
15V
MAX630
+V
S
I
C
V
FB
GND
4
MAX630
LBR
+V
S
I
C
5
6
7
100kΩ
280kΩ
8
LBD
GND
4
V
FB
C
X
2
47pF
POWER FAIL
Figure 5. 3V to 5V Converter with Low-Battery Frequency Shift
Figure 6. Uninterruptable +5V Supply
1.0mH
9V
BATTERY
2.4MΩ
8
1.3MΩ
10MΩ
1MΩ
3
L
X
5
+V
S
I
C
6
7
2MΩ
470μF
25V
MAX8212
2
3
HYST
THRESHOLD
1MΩ
OUT
1
MAX630
LBR
V
FB
390kΩ
GND
5
LBD
8
100pF
C
X
2
GND
4
560kΩ
47pF
Figure 7. Battery Life Extension Down to 3V In
______________________________________________________________________________________
11
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
