Line Transformers

[aibelectronics]

I open my phone recharger and I see this small transformer (line transformer); there seem to be hardly a bridge rectifier present, just resistors and some lonely capacitors and diodes.

How does the line transformer work? Has anybody seen a circuit on how to use it? Does it have any power handling limitations? For I see them mostly in low power consuming devices.

 

[j.p.bill]

The transformer is not center tapped, so a bridge rectifier would be wasted. The beast just half wave rectifies and sort of smoothes the ripple with the caps. The output voltage is only accurate when the load is close to the current rating. Batteries are pretty unconcerned about the quality if the DC that charges them.

The rating for the output is usually moulded into the plastic case. You can bet that the charger's wall wart has just enough poop to do the charging.

 

[aibelectronics]

Sorry I think what I meant to say was 'current transformer' and not 'line transformer'?

 

[ronsimpson]

current transformer

If you really mean current transformer then: There are many different types. Some are square boxes with two large high current leads and two low current leads. There is a kind like in the link below where you run a wire through the center of a coil.
**broken link removed**
**broken link removed**
Some are for 50/60hz and some are for 1khz-200khz.

To directly measure power line current you could cut open the power line and insert a 0.01 ohm resistor. (find one first) measure 0.01 volts/Amp. Watch out do not get shocked.
OR
Run the hot power line wire through a 100:1 current transformer. Put a 100 ohm resistor on the secondary. Now you have isolation from the power line. The 0.01 volts is multiplied up to 1 volt. You can safely measure 1V/1Amp. Using a small 100 ohm resistor.