A very simple 5 W constant voltage ,constant current (CV/CC) universal-input power supply for cell phone or similar charger applications can be designed using the LNK616PG product from the LinkSwitch-II family.
The LNK616PG was developed to cost effectively replace all existing solutions in lowpower charger and adapter applications. Its core controller is optimized for constant voltage , constant current charging applications with minimal external parts count and very tight control of both the output voltage and current, without the use of an optocoupler.
The LNK616PG has an integrated 700 V switching MOSFET and ON/OFF control function which together deliver high efficiency under all load conditions and low no-load energy consumption.
The LNK616PG also provides a sophisticated range of protection features including autorestart for control loop component open/short circuit faults and output short circuit conditions. Accurate hysteretic thermal shutdown ensures safe average PCB temperatures under all conditions.
This circuit uses the LNK616PG in a primary-side regulated flyback power-supply configuration.
The AC input power is rectified by diodes D1 through D4. The rectified DC is filtered by the bulk storage capacitors C1 and C2. Inductors L1 and L2, with capacitors C1 and C2, form pi filters to attenuate conducted differential-mode EMI noise.
The rectified and filtered input voltage is applied to one end of the transformer (T1) primary winding. The other side of the transformer’s primary winding is driven by the internal MOSFET of U1. An RCD-R clamp consisting of D5, R3, R4, and C3 limits drain voltage spikes caused by leakage inductance.
Transformer T1’s secondary is rectified by D7, a Schottky barrier-type diode (chosen for higher efficiency), and filtered by C7 and C8.
The LNK616PG regulates output using ON/OFF control for constant voltage regulation, and frequency control for constant current regulation. The output voltage is sensed by a bias winding on the transformer.
Resistor R9 provides a minimum load to maintain output regulation when the output is unloaded.
For T1 transformer you can be used transformers from Santronics type SNXR1346 , Ice Components TP07161 or Precision, Inc 019-6120-00R.
As you can see in the circuit diagram , this low cost charger, adapter accepts a wide range of input voltage , from 85 VAC up to 265 VAC and will provide a fixed 5 volt DC output at a maximum output current of 1 ampere.
