TOUCH CONTROL HALOGEN LAMP DIMMER

FEATURES:

• Touch or pushbutton control of incandescent lamps

and *transformer-coupled halogen lamps.

*Magnetic transformers and most Electronic transformers

• Direct replacement for P/N SLB0587

(See “DISCUSSION” on Page 3)

• Automatic safety shutdown

• PLL synchronization allows use as a Wall Switch

• Three operating modes

• Extension input for remote activation

• 50Hz/60Hz AC line frequency

• LS7631, LS7632 (DIP); LS7631-S, LS7632-S (SOIC)

- See Figure 1 -

APPLICATIONS:

Electronic dimmers for wall switch control of ceiling mounted

lighting, foot switch control of large floor lamps and hand switch

control of table lamps.

BACKGROUND AND GENERAL DESCRIPTION:

A typical electronic dimmer may not operate properly with the in-

ductive load encountered when driving a magnetic transformer-

coupled low-voltage halogen lamp. The inductive load can cause

a phenomenon called half-waving, wherein the triac fires in al-

ternate half-cycles only, which may lead to the thermal de-

struction of the load transformer. The problems encountered in

driving an inductive load are addressed by the LS7631/LS7632

CMOS ICs as follows:

1. Compensation for delayed triac cut-off.

When a trigger pulse is due to occur at a conduction

angle which coincides with the on-state of the triac,

the trigger pulse is delayed until the triac has turned off.

This eliminates the underlying cause of half-waving.

.

2. Compensation for delayed triac turn-on.

At the set conduction angle, a triac trigger pulse of 130.2µs

(60Hz) is issued by the IC. If the triac fails to fire, a second

trigger pulse of 260.4µs width is issued 1ms later as a

second attempt to fire the triac during the same half-cycle.

3. Safety-shutdown.

If the frequency of occurrences of the delayed turn-on exceeds

a preset threshold, a shutdown is initiated by turning off the

triac trigger pulses. The safety-shutdown threshold value is

accumulated in a 4-bit Up/Down counter. The count

increments for every occurrence of delayed turn-on and

decrements once every 8 SYNC pulses (AC line cycles).

The counter will not decrement below zero. If the count

reaches 15, the safety-shut-down is effected.

INPUT/OUTPUT DESCRIPTION:

Vss (Pin 7) Supply voltage negative terminal.

MODE (Pin 2) - See Table 1

Both LS7631 and LS7632 can operate in 3 different modes.

The 3-state MODE input selects the operating modes:

CAP (Pin 3) - PLL filter capacitor input. See Figure 5.

SYNC (Pin 4) - See Figure 5

The AC line frequency is applied to this input. All internal timings

are synchronized to the AC phase through a PLL circuit.

The Load On/Off status information is also derived from this input.

SENS (Pin 5) - See Table 1

A Logic 0 applied to this input alters the TRIG output either by

turning it on, turning it off or by changing its conduction angle.

Specifically which action takes place is dependent on the type of

activation of the SENS input, namely SHORT or LONG touch

and the prior state of TRIG output.

EXT (Pin 6)

Same functionality as the SENS input, except that a Logic 1 is the

active level at this input. EXT input is intended to be operated

from a remote site with long cable connection, when noise can be

expected. The sampling method used at this input makes it less

sensitive to noise.

TRIG (Pin 8)

The TRIG output is a low level pulse occurring once every half-

cycle of the AC and is intended to drive the gate of a triac in se-

ries with the load. The conduction angle, ø, of the TRIG pulse can

be varied by means of LONG and SHORT touches at either the

SENS or the EXT input.

December 2005

7631-120505-1

LSI/CSI

LSI Computer Systems, Inc. 1235 Walt Whitman Road, Melville, NY 11747 (631) 271-0400 FAX (631) 271-0405

UL

®

A3800

PIN ASSIGNMENT - TOP VIEW

LS7631

LS7632

1

2

3

4

8

7

6

5

EXT

MODE

CAP

SYNC

FIGURE 1

TRIG

SENS