FIGURE 4. TOUCH LAMP APPLICATION SCHEMATIC
+V
LOAD
D1
R1
MT2
MT1
+
-
T1
C1
R5
+
-
Z1
AC
MAINS
C6
G
-V
(SEE NOTE 1)
C5
C2
8
TRIG
7
6
5
VSS
MODE CONT
C7* (SEE NOTE 2)
LS7538
CLOCK SYNC VDD TOUCH
2
4
1
3
R2
D3
D2
R4
R3
TOUCH
PLATE
(LAMP BODY)
C3
C4
115VAC APPLICATION
220VAC APPLICATION
R1 = 20kW, 1W
R2 = 470kW, 1/4W
R3 = 1kW, 1/4W
C4 = 1000pF, 1kV
C5 = .03µF, 16V
C6 = 1µF, 16V
Z1 = 8.2V, 1/4W Zener
D1 = 1N4004
D2 = 1N4148
D3 = 1N4148
T1 = Q2004L4 (Typical Triac)
or Q2004F41 (Typical Triac)
R1 =
R2 =
(1) R4 =
D1 =
T1 =
or
39kW, 2W
910kW, 1/4W
360kW, 1/4W, 1%
1N4005
Q4004L4 (Typical Triac)
Q4004F41 (Typical Triac)
(1) R4 = 300kW, 1/4W, 1%
R5 = 10MW, 1/4W
C1 = 47µF, 16V
C2 = 1000pF, 16V
C3 = 1000pF, 1kV
All other values remain the same.
(1) Resistor should be placed adjacent to Pin 1.
NOTE 1: Connect MODE (Pin 6) for desired Brightness Step Sequence (See Table 1).
NOTE 2: A good PCB layout using through-hole components will provide protection for ESD introduced at the Touch Plate in the range
of 25kV. Using surface mount components and/or a poor PCB layout can reduce the ESD protection. The OEM can increase the ESD
protection provided by the product with any combination of the following steps:
Step 1: The most effective and least costly way to increase ESD protection is to create a spark gap around the Touch Plate input on
the PCB. This will increase ESD protection on a good PCB layout to abut 35kV. The gap should be made with a split metal ring with
each side of the metal ring connected back to opposite sides of the AC line. This ensures that a path for the spark back to house ground
through AC Neutral exists independent of line plug polarity. The split ring and the center conduction plate should be constructed so that
the spacing between them conforms to UL requirements. The spark gap will absorb most of the ESD leaving a remnant of about 10kV
for the rest of the circuit to absorb.
Step 2: Increase R3 from 1kWto 5.1kWand add C7, a 0.1µF capacitor, between VDD and Vss.
(A minimal loss in touch sensitivity may be experienced.)
Step 3: Replace diodes D2 and D3 (1N4148) with Schottky diodes (1N5819 or similar)
7538/39-091100-4
LSI [ LSI COMPUTER SYSTEMS ]
