TOUCH CONTROL HALOGEN LAMP DIMMER

FEATURES:

• Touch or pushbutton control of incandescent lamps

and transformer-coupled halogen lamps

• Works with Magnetic or ElectronicTransformers

• Automatic Safety Shutdown

• Three operating modes

• Extension input for remote activation

• 50Hz/60Hz AC line frequency

• LS7634, LS7635 (DIP); LS7634-S, LS7635-S (SOIC);

LS7634FO, LS7635FO (DIP);

LS7634FO-S, LS7635FO-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 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 LS7634/LS7635

family of CMOS ICs as follows:

1. 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. Delayed triac turn-on and safety shutdown

With inductive loads, the holding current needed to maintain

the triac On-State, may seriously lag behind the gate trigger

signal causing the triac to turn off prematurely. 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

All variations of LS7634 and LS7635 can operate in 3 different

modes. The 3-state MODE input selects the operating modes:

SYNC (Pin 4) - See Figure 6

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

are synchronized to the AC. 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.

Test (Pin 3)

For factory use only.

September 2006

7634/7635-090606-1

LSI/CSI

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

UL

®

A3800

LS7634 LS7635

LS7634FO LS7635FO

1

2

3

4

8

7

6

5

EXT

MODE

SYNC

FIGURE 1

TRIG

SENS

PIN ASSIGNMENT - TOP VIEW

TEST