Gyrator Circuit

Description

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.

Circuit Notes

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, H_FE of the transistor. In this circuit C2, a 100uF capacitor is effectively magnified at the ouput ( Vreg ). If you assume a dc current gain, H_FE 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.