TOUCH CONTROL LAMP STEP DIMMER
DESCRIPTION:
LS7237 is a MOS integrated circuit designed to control
the brightness of an incandescent lamp. The output of the
LS7237 triggers a triac connected in series with a lamp
(See Figure 5). The lamp brightness is determined by
controlling the output conduction angle (triac triggering
angle) in relation to the AC line frequency (See Figure 2).
The output conduction angle can be varied by applying a
low level pulse at the SENS input or a high level pulse at
the EXT input. When implemented as shown in Figure 5,
this is accomplished by touching the Touch Plate which
causes the lamp brightness to change in specified steps
as follows:
LEVEL BRIGHTNESS (% Rated Wattage)
Off
0
Night Light
9
Mood Light
29
Medium
66
Maximum
99
The LS7237 can operate in one of three different modes
selected by the MODE input. The Brightness Sequences
produced by the different modes are as follows:
MODE
BRIGHTNESS SEQUENCE
0
Off-Max-Off
1
Off-Mood-Med-Max-Off
2
Off-Night-Mood-Med-Max-Off
After AC power-up, the output comes up in the OFF state.
Following that, every time the Touch Plate is touched, the
output steps to the next level of brightness. The next step
following the maximum brightness is the OFF state, in-
itiating a new sequence.
1
2
3
4
8
7
6
5
LS7237
V
DD
(-V)
MODE
CAP
SYNC
TRIG
V
SS
(+V)
EXT
S E N S
FIGURE 1
PIN ASSIGNMENT - TOP VIEW
STANDARD 8 PIN PLASTIC DIP
LSI
7237-012703-1
January 2003
INPUT/OUTPUT DESCRIPTION:
V
SS
(Pin 1)
Supply voltage positive terminal.
MODE (Pin 2)
The operating mode for the circuit is selected by con-
necting this input as follows:
MODE INPUT SELECTED MODE
V
SS
Mode 0
V
DD
Mode 1
Float
Mode 2
CAP (Pin 3)
PLL filter input capacitor. A 0.047F capacitor should be
connected to this input.
SYNC (Pin 4)
The AC Line Frequency is applied to this input through an
external RC circuit (See Figure 5). The Phase-Lock Loop
in the IC synchronizes all internal timings to the AC signal
at the SYNC input.
SENS (Pin 5)
A low-level pulse applied to this input causes the TRIG out-
put to step to the next conduction angle in the sequence
selected by the MODE input. The change in conduction an-
gle takes place with the trailing edge of the SENS input
pulse.
FEATURES:
PLL synchronization allows use as a Wall Switch
Provides brightness control of an incandescent lamp
with a touch plate or pushbutton switch
Can control speed of shaded pole and universal AC motors
Controls the "duty cycle" from 23% to 88% (conduction
angles for AC half-cycles between 45 and 158, respectively)
Operates at 50Hz/60Hz line frequency
Extension input for remote activation
+12V to +18V (V
SS -
V
DD
)
LS7237 (DIP); LS7237-S (SOIC) - See Figure 1
LSI/CSI
LSI Computer Systems, Inc. 1235 Walt Whitman Road, Melville, NY 11747 (631) 271-0400 FAX (631) 271-0405
LS7237
UL
A3800
The information included herein is believed to be
accurate and reliable. However, LSI Computer Systems,
Inc. assumes no responsibilities for inaccuracies, nor for
any infringements of patent rights of others which may
result from its use.
CONDUCTION ANGLE, BRIGHTNESS LEVEL
No output
Off
45
Night Light
70
Mood Light
105
Medium
158
Maximum
NOTE: In the schematic shown in Figure 5, the SYNC Input sig-
nal is delayed in phase with respect to the AC Line by about 7.
This delay reduces the conduction angle, with respect to the
AC Line by 7 from the values shown above.
7237-012703-2
TRIG
S Y N C
T
W
T
W
FIGURE 2. TRIG OUTPUT CONDUCTION ANGLE,
EXT (Pin 6)
The EXT input is functionally similar to the SENS input with
the exception that a high-level pulse is the active signal. It is
recommended that the EXT input be used instead of the
SENS input when long extension wires are used between the
IC and the sensing circuitry (See Figure 5 and Figure 6) be-
cause the EXT input is less susceptible to "Noise".
V
DD
(Pin 7)
Supply voltage negative terminal.
TRIG (Pin 8)
The TRIG output is a low-level pulse of fixed duration oc-
curring once every half-cycle of the SYNC input. The con-
duction angle, of the output in relation to the SYNC signal
controls the lamp brightness. The 5 levels of brightness cor-
respond to the 5 values of as follows:
S E N S
, M O D E 0
, M O D E 1
, M O D E 2
T
S1
OFF
OFF
OFF
70
45
OFF
105
70
158
158
105
OFF
OFF
158
158
70
OFF
FIGURE 3. TRIG OUTPUT CONDUCTION ANGLE, , VS SENS INPUT
158
ABSOLUTE MAXIMUM RATINGS:
PARAMETER SYMBOL VALUE UNIT
DC Supply Voltage
V
SS
+20
V
Any Input Voltage
V
IN
V
SS
-20 to V
SS
+0.5
V
Operating Temperature
T
A
0 to +80
C
Storage Temperature
T
STG
-65 to +150
C
DC ELECTRICAL CHARACTERISTICS:
(T
A
= 25C, all voltages referenced to V
DD
)
PARAMETER SYMBOL
MIN
TYPE MAX UNIT CONDITION
Supply Voltage V
SS
+12
+18
V -
Supply Current
I
SS
1.0
1.4
mA V
SS
= +15V,
output off
Input Voltages:
MODE LO
V
IZL
0
V
SS
- 9
V -
MODE HI
V
IZH
V
SS
- 1.5
V
SS
V -
SYNC LO
V
IRL
0
V
SS
- 9.5
V -
SYNC HI
V
IRH
V
SS
- 5.5
V
SS
V -
SENS LO
V
IOL
0
V
SS
- 8
V -
SENS HI
V
IOH
V
SS
- 2
V
SS
V -
EXT LO
V
IVL
0
V
SS
- 8
V -
EXT HI
V
IVH
V
SS
- 2
V
SS
V -
Input Current:
SYNC, SENS, EXT HI
I
IH
110
A With Series 1.5M
Resistor to
115VAC Line
SYNC, SENS, EXT LO
I
L
100
nA -
TRIG HI Voltage
V
OH
V
SS
V -
TRIG LO Voltage
V
OL
V
SS
- 8
V V
SS
= +15V
TRIG Sink Current
I
OS
25
mA V
SS
= +15V
V
OL
= V
SS
- 4V
TIMING CHARACTERISTICS (See Figures 2 and 3):
All timings are based on fs = 60Hz, unless otherwise specified. 50Hz timings are 1.2 times 60Hz timings.
PARAMETER
SYMBOL
MIN TYPE MAX
UNIT
SYNC Frequency
fs
40
-
70
Hz
SENS/EXT Duration
T
S1
50
-
Infinite
ms
TRIG Pulse Width
T
W
-
33
-
s
7237-012703-3
OUTPUT
DRIVER
DIGITAL
COMPARATOR
MEMORY
PHASE
LOCK
LOOP
CONTROL
LOGIC
BUF
BUF
BUF
BUF
SYNC
CAP
MODE
EXT
SENS
V
SS
V
DD
FIGURE 4
LS7237 BLOCK DIAGRAM
4
3
2
6
5
1
7
(+V)
(-V)
8
TRIG
POINTER
C1 = 0.15F, 200V
R4 = 1M
to 5M
, 1/4W
C2 = 0.33F, 200V
(Select for sensitivity)
C3 = 0.047F, 25V
R5, R6 = 2.7M
, 1/4W
C4 = 470pF, 25V
R7 = 150k
, 1/4W
C5 = 47F, 25V
R8 = 100
, 1/4W
C6 = 680pF, 25V
D1 = IN4148
C7 = 0.1F, 25V
Z = 15V, 1W (Zener)
R1 = 270
, 1W
T = Q4006L4 Triac (Typical)
R2 = 1.5M
, 1/4W
L = 100H (RFI Filter)
R3 = 1.5M
, 1/4W
(1) For Connection A. Use 0.22F for Connection B.
(2) For Connection A, Modes 1 and 2.
Use 1/4W for Mode 0 and Connection B, all Modes.
C1 = 0.15F, 400V
R4 = 1M
to 5M
, 1/4W
C2 = 0.22F, 400V
(Select for sensitivity)
C3 = 0.047F, 25V
R5, R6 = 4.7M
, 1/4W
C4 = 470pF, 25V
R7 = 150k
, 1/4W
C5 = 47F, 25V
R8 = 100
, 1/4W
C6 = 680pF, 25V
D1 = 1N4148
C7 = 0.1F, 25V
Z = 15V, 1W (Zener)
R1 = 1k
, 2W
T = Q5004L4 Triac (Typical)
R2 = 1.5M
, 1/4W
L = 200H (RFI Filter)
R3 = 1.5M
, 1/4W
(3) For Connection A. Use 0.1F for Connection B.
(4) For Connection A, Modes 1 and 2.
Use 1/4W for Mode 0 and Connection B, all Modes.
N O T E S :
P
115VAC
OR
220VAC
N
LOAD
C1
T
L
C2
R1
R2
A
B
R8
R3
C5
D1
1
2
3
4
8
7
6
5
R4
C3
C4
TRIG VDD EXT SENS
VSS MODE CAP SYNC
+
SEE NOTE 3
L S 7 2 3 7
R6
R5
FIGURE 5. A Typical Lamp Dimmer
G
Z
-
ELECTRONIC
EXTENSION
(FIG. 6)
EXTN
P
C7
SEE NOTE 4
SEE NOTE 2
R7
C6
TOUCH
PLATE
MT2
MT1
1) All circuits connected by broken lines are optional.
2) C7 is used only with electronic extension and R7 is used only with mechanical switch
3) Use Connection A when Neutral is not available. Use Connection B when Neutral is available.
4) Connection between Pin 6 and Pin 7 should be broken when EXT is used.
(1)
115V
220V
7237-012703-4
APPLICATION EXAMPLES:
A typical implementation of a lamp dimmer circuit is shown in Fig. 5.
Here the brightness of the lamp is set by touching the Touch Plate .
The functions of different components are as follows:
The 15V DC supply for the chip is provided by Z, D1, R1, C2, C5.
R2 and C4 generate the filtered signal for the SYNC input for syn-
chronizing the internal PLL with the line frequency.
R3 and C7 act as filter circuit for the electronic extension. If exten-
sions are not used, the EXT input (Pin 6) should be tied to V
DD
(Pin 7).
R4, R5, R6 set up the sensitivity of the SENS input. C6 provides
noise filtering.
C3 is the filter capacitor for the internal PLL.
R8 provides current limiting and isolation between the chip output
and the triac gate.
C1 and L are RF filter circuits.
In the case of momentary power failure, the circuit state remains un-
changed for a period up to 1 sec. For longer power interruptions, the
output is shut off.
EXTENSIONS:
All switching and dimming functions can also be implemented by
utilizing the EXT input. This can be done by either a pushbuttonl
switch or the electronic switch in conjunction with a Touch Plate
as shown in Figure 6. When the plate is touched, a logic high lev-
el is generated at the EXT input of the IC for both half-cycles of
the line frequency. (See Figure 5)
EXTN
2K
,1/4W
IN914
TOUCH PLATE
*R
200K
,1/4W
MPS8599
FIGURE 6. ELECTRONIC EXTENSION
P
*R
*R
=
2M
, 1/4W for 115VAC
*R
=
3.6M
, 1/4W for 220VAC
(2)
(3)
(4)
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