TOUCH CONTROL LAMP DIMMER

DESCRIPTION:

LS7231 through LS7234 are a series of monolithic, MOS

integrated circuits designed for the control of brightness of

incandescent lamps. The outputs of these ICs control the

brightness of a lamp by controlling the firing angle of a

triac connected in series with the lamp. All internal timings

are synchronized with the line frequency by means of a

built-in phase-lock loop circuit. The output occurs once

every half-cycle of the line frequency. Within the half-

cycle, the output can be positioned anywhere between

158˚conduction angle for maximum brightness and 41˚

conduction angle for minimum brightness in relation to the

AC line frequency. The positioning of the output is con-

trolled by applying a low level at the SENS input or a high

level at the EXT input.

These functions may be implemented with very few inter-

face components, as shown in Figure 5. When imple-

mented in this manner, touching of the Touch Plate caus-

es the lamp brightness to change as follows:

1.

If the Touch Plate is touched momentarily (42ms to

333ms), the lamp is:

a) turned off if it was on,

b) turned on if it was off.

The brightness resulting is either full brightness or

depending on the circuit type, a previous brightness

stored in the IC memory.

2. If the Touch Plate is touched for a prolonged time

(more than 342ms) the light intensity changes slowly.

As long as the touch is maintained, the change con-

tinues; the direction of change reverses whenever the

maximum or minimum brightness is reached.

1

2

3

4

8

7

6

5

TRIG

EXT

SENS

DOZE

CAP

SYNC

FIGURE 1

PIN ASSIGNMENT - TOP VIEW

The IC also provides an input for slow dimming. By

applying a slow clock to this input, the lamp can be

dimmed slowly until total turn off occurs. This fea-

ture can be useful at bedtime in a child’s room.

INPUT/OUTPUT DESCRIPTION:

Supply voltage positive terminal.

DOZE (Pin 2)

A clock applied to this input causes the brightness to de-

crease in equal increments with each negative transition

of the clock. Eventually, when the lamp turns off, this in-

put has no further effect. The lamp can be turned on

again by activating either the SENS input or the EXT in-

put. For the transition from maximum brightness to off, a

total of 83 clock pulses are needed at the DOZE input.

When either the SENS or the EXT input is active, the

DOZE input is disabled. (See Figure 7)

CAP (Pin 3)

The CAP input is for the PLL filter capacitor. A 0.047µF

capacitor should be connected to this input.

7231-4-120100-1

December 2000

FEATURES:

•

Phase-lock loop synchronization allows use in Wall

Switch applications.

•

Provides brightness control of incandescent lamps

with touch plates or mechanical switches.

•

Controls the "duty cycle" from 23% to 88%

(conduction angles for AC half-cycles between 41˚

and 158˚, respectively.)

•

Operates at 50Hz/60Hz line frequency.

•

Extension input for remote activation.

•

Input for slow dimming.

•

•

LS7231 to LS7234 (DIP) - See Figure 1

LS7231-S to LS7234-S (SOIC)

LSI/CSI

LSI Computer Systems, Inc. 1235 Walt Whitman Road, Melville, NY 11747

(631) 271-0400 FAX (631) 271-0405

LS7231-7234

UL

®

A3800