What isthe blue block in power supply?

[ahgu]

The blue block in any AC adaptor? It is in parallel with the AC input. 1M resistance. Is it for high voltage protection? What is its name?

Also, anyone has schematics for 110-240V input 12V or 5V commercial grade power adaptor schematics? say like 2A.

thanks
Ahgu

 

[Bagster]

These are usually noise supressors or mains suppression capacitors. They aree genrally rated to 440V and have capacitances around 0.1 to 2.2 uF.
For a schematic, use a geneal stepdown transformer and a linear regulator. If you are very careful you can just rectify the mains directly to get dc and then use a large (1M ohm resistor to drop the voltage) This will only work for very low currents.
Best off using a switch mode for high currents. Infineon have some good appnotes and parts you could use, that take mains voltages directly into them.

 

[Frosty]

If you have a 'blue block' directly across L&N then it is most likeley a MOV suppresor.

If its across L or N to earth connection then it is probably a Y class cap.

For 12v @ 2A you could use SMPS solution from PI.

Check out h##p://www.powerint.com/dak.htm

They have 12v supply design 'ready to go'. Already built, tested with results.

STM also have a similar solution using 'Viper'.

You should d/l these apps notes and designs and look for yourself.

R