Component Parts of Rectifier Filters

Author: J.B. Hoag

Fig. 11 H. A typical rectifier circuit

Figure 11 H shows the complete circuit of a typical rectifier. The chokes or coils are wound on iron cores which have a small air gap. The air gap helps to maintain the inductance of the coil at a high value (10 to 30 henries) even when comparatively large currents pass through the coil. Since the inductance does vary somewhat with current, the specification of the inductance can only be given with accuracy for a given current.

For voltages up to approximately 800, the compact, high-capacity electrolytic-type of condenser is used. For still higher voltages, the insulator or dielectric of the condenser is usually made of thin, oil-impregnated paper. Care must be taken to choose a condenser whose continuous-operation or working voltage is high enough so that it will not be punctured. The capacitance of each condenser is usually 4 or 8 μfd., although 16 and even 100 μfd. are occasionally used.

The high resistance BR in the circuits of Fig. 11 G is called a "bleeder-resistance" and is used to discharge the condensers after the power is removed. It should not pass more than 10 per cent of the output current. For small rectifier units ("B-battery eliminators"), a typical bleeder resistor would have 15,000 ohms resistance and 25 watts power-dissipating ability.