An electronic recitification circuit. The use of large, heavy and expensive electrolytic capacitors is avoided, being replaced by an active transistor in this gyrator circuit.
To avoid excess ripple output on a power supply feeding a heavy load, usually a large value capacitor is
chosen following the rectifier. In this circuit, C1's value is only a 470uF. The gyrator circuit works on
the principle that the value of input capacitance at the base-emitter terminals of a transitor is effectively multiplied by the static forward current gain, HFE
of the transistor. In this circuit C2, a 100uF
capacitor is effectively magnified at the ouput ( Vreg ).
If you assume a dc current gain, HFE of 50 for the 2N3055 power transistor, then the effective
value of the smoothing capacitor would be 50x this value; or be the same as using a 5000uF capacitor without
the power transistor. The graph below shows the output voltage and current through the load :-
The load draws nearly 400mA. With the output directly from the rectifier there is about 5v pk-pk ripple
in the output. Using the output at the emitter of the transistor things are much better. The circuit will
take a few hundred milliseconds for the output voltage to stabilize and reach maximum value. The
advantages are that a smaller, less costly reservoir capacitor can be used with this circuit to give a
high quality smoothed supply.