Connecting a MCU to mains power

[Hell-e-Guy]

Hi,
What's the best way to connect a MCU and different peripherals to 220VAC.
I will require 3.3V and around 100mA.
I have seen the zener approach with a series resistor and capacitor,
but I don't like this non isolated topology.
Are there small 0.5W universal offline regulators?
Whats the smallest 50Hz iron transformer that can be found?

Hell-e

[jeffs555]

The best way is probaby with a wall wart. Most of the wall chargers for cell phones, PDA's etc, are simple current limited dc supplies with an unregulated output around 5 volts. Add a 3.3v regulator and a couple caps to your MCU board, and you are all set.

[Hell-e-Guy]

Thanks jeffs555,
Do you have any particular one in mind (as small as possible)....
I have a couple of old Nokia chargers but they are too big.

Hell-e

[vintage1]

Hi,
What's the best way to connect a MCU and different peripherals to 220VAC.
I will require 3.3V and around 100mA.


100mA at line voltage(US) is 10W..no you don;t want a dropper do you? :rolleyes:

I have seen the zener approach with a series resistor and capacitor,
but I don't like this non isolated topology.
Are there small 0.5W universal offline regulators?

Yup

Whats the smallest 50Hz iron transformer that can be found?

Pretty small, but they don't come cheap..the wall wart size is the cheapest - reasonable gauge wire in those..

http://www.circuitspecialists.com/prod.itml/icOid/1708

Cheap enough, and pretty small.


You should be able to get a 5W 5v type transformer, and a teensy bridge rectifier

http://www.circuitspecialists.com/prod.itml/icOid/3387

and a small capacitor

http://www.circuitspecialists.com/prod.itml/icOid/3149

and a 3.3v regulator

http://www.circuitspecialists.com/prod.itml/icOid/4205

for not much at all. These are TO92 style regulators that are ideal for this.

You will need a couple of resistors and capacitors more for RF suppression and to set the output voltage.