Problem: Choose a type of rectifier tube suitable for use in a single-phase, full-wave power supply to deliver a total average current of 500 milliamperes at a maximum d-c voltage of 2385 volts. Also, for what maximum secondary voltage (Ebms) should the transformer be designed in order to deliver 2385 volts to the filter at maximum load current.

Procedure: First, determine the maximum peak inverse voltage which each rectifier tube must withstand. By reference to the relations shown for the single-phase, full-wave circuit (Fig. 20 in the above table), it is found that the maximum peak inverse voltage corresponding to a d-c voltage of 2385 volts is 3.14x 2385, or 7489 volts. Since two half-wave rectifiers will be required in this service, each rectifier will only have to deliver 500/2, or 250 milliamperes. A rectifier tube meeting these voltage and current requirements is the RCA-866, with a peak inverse voltage rating of 7500 volts and an average plate current rating of 250 milliamperes. In order to deliver 2385 volts to the filter at maximum load, the transformer should be designed so that each half of the secondary will produce an Ebms of 1.11 x2385, or 2647 volts.

The percentage change in output voltage of the power supply between no-load and full-load conditions is known as voltage regulation. For example, if the d-c output voltage is 1000 volts at no load and is 900 volts at full load, the voltage regulation is (1000-900)/1000 = 0.1, or 10%. Well-designed power supplies have

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