This is the LED indicator for show AC current load, that use the transformer and LED as based of circuit.
Sometimes we need to detect the large AC current. One way is the LEDs is connected with the resistors and the diode 1N4001 networks. But this have disadvantage is voltage drop across too much.
There is best ways by use the current transformer, advantage of this way is current that will check, can convert to neat instrument. And, The transformer also helps to separate the current to be measured with a meter out. Which are very useful in measuring current or voltage high.
This transformer may use normal transformer by the lower voltage coil is connected to the high current. And the primary coil connect to the LED or them meter. In selecting the transformer: Maximum current of the secondary coil And a maximum current of the LED is determined as follows.
Example: The current detector is 0.6A. Thus the lower coil will must can tolerate this current size. Assuming that the maximum current For the measurement is 30 mA must select a transformer 220 volts is 12 volts. To get an accurate conversion ratio (600/30).
The voltage loss to drop across the coil of the transformer is very low. And Leakage current across the coil of the transformer is very low and may abandon it. Thus the voltage loss so as the LED voltage divided by the ratio of the transformer.
The secondary coil of transformer must to connect to load all times so we have the four diode as bridge to show both positive and negative wave form. If no load the secondary coil will be normal coil.