Circuit Design of 2.75W High Efficiency Constant Voltage/Constant Current Output USB Charger

Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

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Summary:

The LinkSwitch-XT flyback power supply converts the AC input voltage from 90VAC to 264VAC into a single isolated DC output voltage. The power supply output is 5V, 550mA (2.75W) constant voltage / constant current (CV / CC). Typical applications include cell phone chargers, portable audio players, digital cameras, and other products with a USB charger interface. Diodes D1, D2, D3, and D4 and capacitors C1 and C2 rectify and smooth the AC input voltage. Differential mode EMI filtering is provided by C1, C2, L1 and L2. Through the integrated frequency modulation function in U1 and the E-Shield technology of the transformer, we can make this simple EMI filter comply with the EN55022B standard, even if the primary and secondary insulation layers do not have a Y capacitor.

design feature

• Standard USB output connector
• High efficiency (>60% under full load)
• Meets CEC/Energy Star 2008 requirements for efficiency in the load mode (up to 63%, 59.1% required)
• Low input power at no load (< 200 mW at 200 VAC AC input)
• Excellent constant voltage and constant current characteristics with overheat protection
• Meet all specifications of China USB charger
• Compliant with CISPR-22/EN55022 B conducted EMI limit (EMI margin > 10dBμV), no Y capacitor required

USB charger (5 V, 550 mA) circuit diagram using LinkSwitch-XT series LNK363DN

See the uploading documentation for details (click to download)