SGL8022W Touch LED PWM Module Schematic Circuit Diagram
A while back, during my eBay search for a straightforward LED controller to modernize my vintage bedroom lamp, I stumbled upon this touch-LED PWM module. To be frank, although it was a fully assembled module and appeared to be well-made, I had some reservations after reviewing the documentation. Upon closer examination of the compact circuit board, I observed that it was built around a single-channel DC LED control touch chip known as SGL8022W (manufactured by Sigma Micro), which was largely in line with my expectations.
Chip Talk
According to Sigma Micro, the SGL8022W is a single-channel touch chip designed for LED brightness control. This chip can manage the on/off status of LED lights and regulate their brightness across a continuous range, making it suitable for use with incandescent and halogen lights. SGL8022W exhibits robust performance, with an EFT (Electrical Fast Transient) tolerance exceeding ±2 KV. This means that its touch sensitivity and response time remain reliable, even when subjected to interference from nearby mobile phones. You can find the pin assignments and descriptions of SGL8022W in its SOP 8 package. Furthermore, the chip supports a relatively wide input voltage range, which can be selected within the range of 2.4 to 5.5 Vdc as needed.
Circuit Surgery
Modifying the module’s circuitry was a straightforward process for me, as I have access to the hardware schematics and possess ample experience as a hardware design engineer. However, upon closer inspection of the module, I noticed that the circuit layout deviated somewhat from the original application example provided in the datasheet. Additionally, there were two unexpected components introduced into the design: a diode and a resistor, along with the inclusion of a “power on” LED and its corresponding current-limiting resistor!
The purpose of the diode is evident; it serves as a safeguard against incorrect input polarity, although it’s worth noting that it introduces a 0.7-V voltage drop since it’s not a Schottky diode. However, the role of the additional component was initially unclear to me. To gain better understanding, I decided to replicate the original circuitry of the FC-106 module, as illustrated below.
In this schematic, we can observe that the component in question is a 36-ohm (36R) resistor, connected between the Vcc rail and the common Vcc points of the mode selection jumpers T1 and T2. My assumption is that this resistor serves as an additional safeguard for the circuit. Additionally, it’s worth mentioning that the touch sensitivity can be adjusted by modifying the value of the sampling capacitor located between pin 2 (VC) and pin 4 (GND) of the SGL8022W chip. It’s important to note that the 100-μF capacitor (C1) featured in the original application circuit is not utilized in this module; you can spot its footprint between the chip and the diode in the module being tested.
Now to the mode selection; i.e., the four mode options determined by the configuration of mode selection jumpers T1 and T2 (as examined by me):
