U® L LSI Computer Systems, Inc. 1235 Walt Whitman Road, Melville, NY 11747 (631) 271-0400 FAX (631) 271-0405
TOUCH CONTROL HALOGEN LAMP DIMMER
• Touch or pushbutton control of high-voltage lamps
and *transformer-coupled low-voltage halogen lamps
*Magnetic Transformers and most Electronic Transformers
• Automatic Safety Shutdown
• Three operating modes
• Extension input for remote activation
• 50Hz/60Hz AC line frequency
• +5V Power Supply (VDD -VSS)
• LS7634, LS7635 (DIP); LS7634-S, LS7635-S (SOIC);
LS7634FO, LS7635FO (DIP);
LS7634FO-S, LS7635FO-S (SOIC)
- See Figure 1 -
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.
PIN ASSIGNMENT - TOP VIEW
VDD (+V ) 1
7 VSS (-V )
VDD (Pin 1) Supply voltage positive terminal.
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:
Vss = Mode 0; Float = Mode 1; VDD = Mode 2
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.