Pre Deled 2026 Examination
Drives the segment or graphic LCD panel, sequentially cycling through the active ports to show real-time voltage and current consumption.
Reduces electrical noise feedback into the AC lines. B. Rectification Stage
[ AC Input: 100-240V ] │ ▼ [ Primary Protection & EMI Filter ] │ ▼ [ Full-Bridge Rectifier & High-Volt DC Bus ] │ ▼ [ PWM Switcher IC & Main Transformer ] ──(Optocoupler Feedback)──┐ │ │ ▼ │ [ Secondary Rectification & LC Filter ] │ │ │ ▼ │ [ 5V Constant Voltage DC Bus ] <──────────────────────────────────┘ │ ├──► [ LED Display & Microcontroller Module ] │ └──► [ 6x Parallel USB Port Matrix with Current Sense Resistors ] Comprehensive Stage-by-Stage Circuit Analysis 1. Primary High-Voltage AC Input Stage
: Uses a standard Switching Mode Power Supply (SMPS) topology. The board contains a high-voltage primary side (AC input, bridge rectifier, and switching MOSFET) and a low-voltage secondary side (rectifiers, filter capacitors, and the USB distribution bus). Common Issues & Repair Findings Wlx-896b Schematic
A discrete bridge rectifier IC converts the AC sine wave into a pulsing high-voltage DC signal. This signal is smoothed out by a large primary bulk electrolytic capacitor (typically rated at 400V, 47µF–68µF).
: A pi-filter comprised of X-capacitors and a common-mode choke coil dampens high-frequency switching noise from feeding back into the wall outlet.
Burned out resistors used for current sensing can cause the digital display to show "0.00A" even when a device is charging. Drives the segment or graphic LCD panel, sequentially
data lines to scale voltages to 9V/2A or 12V/1.5V on demand.
: An EL817 or equivalent optocoupler straddles the isolation barrier, communicating with a TL431 precision shunt regulator on the low-voltage side to dynamically tune the PWM duty cycle, locking the main output rail at a stable 5.1V to 5.2V DC.
LED/LCD screen for real-time monitoring of voltage and current per port. 2. Schematic Functional Blocks Rectification Stage [ AC Input: 100-240V ] │
(For experienced users only):
A classic pi-filter configuration that filters out high-frequency switching noise, preventing it from feeding back into your home or shop electrical grid. 2. Primary Rectification & High-Voltage DC Bus
When looking at the PCB layout (which mirrors the schematic), you will notice that the board is divided into the "hot" (primary) and "cold" (secondary) sides, separated by an isolation gap for safety.
: A dedicated fast-charging IC handles negotiation protocols (Qualcomm Quick Charge) with attached devices, signaling a local buck-boost converter to step up the local port voltage to 9V or 12V when requested.
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