12V/120mA switch mode power supply circuit.
Transformer less switch mode power supplies have become very popular these days. The circuit shown below is of a 12V/120mA output, 85 to 230V AC input transformerless switch mode power supply using LNK304 IC. Applications of a power supply based on this IC includes hand held devices, timers, small appliances, LED drivers, industrial gadgets etc.
LNK304 is a low component count,
efficient off-line switcher IC that can support buck, buck-boost and
flyback topologies. The IC has a built in auto start circuit for short
circuit and open loop fault protection. Other features of LNK304
includes low temperature variation, thermal shut down,high break down
voltage, good line & load regulation, high band width , wide input
voltage range (85 to 230V AC) etc. In general the LNK304 has a better
performance when compared to the many other discrete buck regulators.
LNK304 pin configuration and typical application
The pin configuration and the typical
application diagram of LNK304 are shown above. Drain (D) pin the drain
connection of the built in power MOSFET. The external by pass capacitor
(0.1uF) is connected to the BYPASS (BP) terminal. FEEDBACK (FB) pin
controls the switching of the built in power MOSFET. A current above
than 49uA delivered to this pin will inhibit the switching. The internal
power MOSFETs source is connected to
