Monday, March 28, 2022

110/220VAC 4 Step Control Touch Dimmer Switch Lamp Circuit with PCB

Fig. 1 110/220VAC 4 Step Control Touch Dimmer Switch Lamp Circuit with PCB

Enhance Your Lighting: Build a 110/220VAC 4-Step Touch Dimmer Switch Circuit for Lamps with PCB Control

This type of circuit is widely used in lampshades that are sold in residential lighting stores, it activates an incandescent bulb through the touch on the device's casing.

It works as a dimmer with 4 pre-set levels, activated by touching a part of the sensor with your finger, which can be a metallic point, or a metallic housing, etc. The entire 4-level brightness control circuit is based on the LS7237 IC.

LS7237 IC Description

LS7237 is a 8-Pin monolithic, MOS integrated circuit designed to control the brightness of an incandescent lamp, as show in Figure 2 above. The output of the LS7237 triggers a Triac connected in series with a lamp. 

Fig. 2 - Pinout LS7237

The lamp brightness is determined by controlling the output conduction angle (Triac triggering angle) in relation to the AC line frequency.


This circuit works directly connected to the 110/220V electrical network, and has a high power load, any carelessness, or wrong connections, error in the project, or any other occasion, can lead to irreversible damage. 

We are not responsible for any type of event. If you do not have enough experience to assemble this circuit, do not do it, and if you do, when testing, be sure to have the proper protections and be accompanied by someone else.

How the Circuit Work

The circuit works as follows: when a touch is made to the board, it causes the brightness of the lamp to change in specified steps as follows:

  • LEVEL - - - BRIGHTNESS(% Rated Wattage)
  • Off .................... 0
  • Night Light ....... 9
  • Mood Light ...... 29
  • Medium ............ 66
  • Maximum ......... 99

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, initiating a new sequence.


  • PLL synchronization allows use as a Wall Switch
  • Provides brightness control of an incandescent lamp with a touch plate or mechanical 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 DC Power Supply (VSS - VDD)
  • 8-Pin Plastic DIP , 8-Pin SOIC

The Schematic Circuit

The 110/220VAC 4 Step Control Touch Dimmer Switch Lamp Circuit diagram is shown in Figure 3 below.  

Is a moderately simple circuit to assemble, with few external components, however one must have at least basic to advanced experience to assemble this circuit, if you are not experienced enough, ask someone more experienced to help you.

Fig. 3 - 110/220VAC 4 Step Control Touch Dimmer Switch Lamp Circuit

110Vac or 220Vac

This circuit was designed to work with 220Vac voltage, for use in 110Vac power network, the following components must be replaced in the component list.

  • R1, R2 .... 2.7MΩ 1/4W (red, violet, red, gold) 
  • R6 ........... 270Ω 1W (red, violet, brown, gold)
  • C5 ........... 330nF / 400V polyester Capacitor 
  • L1 .......... 60µH (RFI Filter)

Components List

  • Semiconductors
    • U1 ............ LS7237 Integrated Circuit
    • Q1 ............ BT136 Triac Transistor
    • D1 ............ 1N4007 Diode
    • DZ1 ......... 1N4744 15V/1W Zenner Diode 

  • Resistor
    • R1, R2 .... 4.7MΩ 1/4W (yellow, violet, green, gold) 
    • R3 ........... 1.8MΩ 1/4W (brown, gray, green, gold)
    • R4 ........... 1.5MΩ 1/4W (brown, yellow, green, gold)
    • R5 ........... 100Ω 1/4W (brown, black, brown, gold)
    • R6 ........... 1KΩ 2W (brown, black, red, gold)
  • Capacitor
    • C1 ........... 680pF / 400V Polyester Capacitor
    • C2 ............47nF / 400V Polyester Capacitor
    • C3 ........... 470pF/ 400V Ceramic Capacitor
    • C4 ........... 47µF / 25V Electrolytic Capacitor 
    • C5 ........... 220nF / 400V Polyester Capacitor
    • C6 ........... 150nF /400V polyester Capacitor

  • Miscellaneous 
    • L1 .......... 120µH (RFI Filter)
    • P1, P2 .... 2-pin PCB soldering terminal blocks
    • F1 .......... 3A/250V Soldering fuse
    • Others .... PCB, heat sink, power supply, wires, etc.

Printed Circuit Board - Download

We are offering the PCB - Printed Circuit Board, in GERBER, PDF and PNG files, for you who want to do the most optimized assembly, either at home.

If you prefer in a company that develops the board, you can is downloading and make the files in the Download option below.

Fig. 4 - PCB 110/220VAC 4 Step Control Touch Dimmer Switch Lamp Circuit

Files to download, Direct Link:

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