AC-to-DC Regulator

(110/220VAC to 5.0VDC)

_______________________________________________________________________________________

7

Polarity Insensitive

Battery-Powered Supply

Figure 12 shows a +5V power supply that works even if

the battery is installed backwards: the full-wave bridge

rectifier of the MAX612 corrects the battery polarity.

The MAX612 is well suited for battery-powered circuits

since its quiescent current is only 70µA. The MAX610

can also be used if the battery voltage is less than 10V.

Battery Charger

The +6.7V open circuit or float voltage of Figure 13 is

set by R2 and R3; the maximum charging current of

60mA is set by the value of C1. Since, unlike trans-

former-driven battery chargers, C1 conducts current

throughout most of each line cycle, the ratio of the RMS

charging current to the average charging current is

only about 1.2:1, and capacitor C2 is optional.

current) (A)

The half-wave MAX611 can also be used in this circuit,

but the value of C1 must be doubled and the ratio of

RMS current to average current increases to about

1.7:1.

MAX611

AC1

5V

LOGIC

LEVEL

LEVEL SHIFTER

OR OPEN-

COLLECTOR

BUFFER SUCH

AS MC14504

OR MM74C907

6

+5V

7

117VAC

POWER

LINE

TO

AC

LOAD

1

4

5

3

N.C.

RD

C1

2

µF

470

µF

15V

R1

47

Ω

1/2W

1M

1k

V-

CONTROL

SYSTEM

V+

OUV

8

+12V OUTPUT

2

AC

LOAD

Figure 10. Driving Triacs with +12V Supply

+12V

+6V

+1.5V

V+

4.65V

0V

OUTPUT

MOMENTARILY

SHORTED

OFF

(OPEN)

ON

OUV

(SINKING CURRENT)

500

5.36V

+1.5V

OUTPUT

SHORTED

TO ANOTHER

POWER SUPPLY

OUV OUTPUT

INDETERMINATE

WHEN V+ < 1.8V

Figure 9b. Power-Up Reset Delay