Full wave precision rectifier

Bridge rectifier with diodes.

What happens if we want to rectify 0.5 volts of the alternating current and convert it into 0.5 volts of the direct current?
Applying the above circuit, the diode bridge rectifier, we won’t obtain an exit (0 volts) between the + and – extremes of the diodes, since the diminution of the power in diodes will prevent the signal from being rectified.

The solution lies in constructing the circuit which will be able to rectify the alternating current practically from 0 volts.
This circuit is our precise full-wave rectifier. It is capable of rectifying the milivolts’ power in the alternating current and converting it to direct current, using the electrolytic condensers’ filters. The circuit is quite simple. We have integrated the source of power so that the assembly can be more compact.

The mentioned source of power is to be symmetric and of +-12 volts so that the integrated circuit TL072 can work properly and the rectification can be effective. The application of this circuit like a full-wave rectifier is perfectly adapted to the necessities of the current clamp for our household.

To create this circuit, we have to rectify the power given by our transformer, which ranges from milivolts to more than 2 volts in the alternating current..

The transformer used in the current clamp.

The electric scheme of the precise full-wave rectified circuit.

The circuit board.

At the pin 7 of TL072 integrated circuit we have the wave rectification of the alternating current and the components C1, C2, C3, R5, R6 form part of the rectification filter so that the output can be a direct current. The diodes 1N4148 rectify the positive half wave.
If we wish to rectify the negative half wave, we have to invert the direction of the diodes.

A photo of the finished circuit.

The 12K trimmer serves to adjust the exit power of the circuit. Turning the mentioned trimmer we can obtain exactly the same volts in direct current at the exit as the ones we had in the alternating current at the entrance.
However, we have exchanged the 12K trimmer for the 5k62 and 1% tolerance resistor, since we have used this prototype for the current clamp. In this assembly, the entrance already has a resistive divider with a trimmer, which serves to adapt the power that will manage the microcontroller pic, and that is why we don’t need to put a trimmer here, in this circuit.

The resistors are all 5k62 and 1% tolerance. They can be substituted for the others of a similar value and the circuit will function just the same.

The scheme and the circuit board should be in the same folder and they should have the same name, you should only change the extension to .sch for the scheme and to .brd for the circuit board, this way both of them will be recognized and associated by Eagle.

The file to download is compressed, to extract it, you should enter a password: www.kemisa.es

If you don´t know how to make a printed circuit boards click here.