Why the transformer is used in rectifier circuit?

Question

vacuum tube rectifier & semiconductor diode rectifier.

Answer 1

It isn't always.

A rectifier converts AC to DC.

A transformer steps AC up or down, to provide a higher or lower voltage.

If you want to convert 120 VAC to 12VDC, you need a step down transformer, followed by a rectifier.

If you want to convert 12VAC to 12VDC, you only need a rectifier.

Answer 2

It doesn't have to be, but then the only AC voltage available would be the 230 volts from the wall outlet. When you rectified and filtered that you would have 320 volts DC.

And there would be no isolation.

Most appliances require a different voltage than 320 volts, so you use a transformer to get that voltage.

And you also get isolation.

.

Answer 3

The transformer in a rectifier power supply circuit serves several purposes.

1- used to change the voltage level from the 115VAC to another level, either higher of lower, to accomadate the needs of the rest of the circuit.

2- provides isolation between the power mains and the circuit power for safety reasons.  If you touch a hot part of the circuit on the secondary side of the transformer while being grounded, you most likely will not get a shock.  If the transformer wasn't in the circuit....you wouldn't be so lucky.  Other than very small leakage currents, no current flow's from the primary side of the transformer to the secondary.

3- Some rectifier circuits require a center reference point.  This is easy to do with a center tapped transformer winding.

4- Many devices require multiple voltage sources.  A transformer can have multiple secondary windings, each wound to produce a different voltage.  An example would be in the tube circuit, where the filaments of a tube might require 6.3vac and the rest of the circuit 600VDC.  The transformer is well suited to provide these multiple outputs.

Answer 4

*When running from an AC source(220V), a transformer is used to transform the incoming mains voltage to the correct value (9V)required for the power supply electronics circuitry.

*The resulting voltage waveform is an alternating current.

*This must be rectified to enable the power to be smoothed and regulated for use by electronics circuitry

Answer 5

http://en.wikipedia.org/wiki/Transformer