Valve Amplifiers by Morgan Jones

Author:Morgan Jones
Language: eng
Format: epub, pdf
ISBN: 978-0-08-096640-3
Publisher: Elsevier Science
Published: 2012-07-20T16:00:00+00:00

where f is the second harmonic of mains frequency.

The reactance of the choke is:

Using Ohm’s law to combine the two equations, the instantaneous current through the choke is:

We are only concerned with the maximum current, which occurs when cos(2 πft)=1, so this factor can be removed, leaving:

It was stated that only the second harmonic was significant, but this assumption should now be examined. Referring to the Fourier series, the fourth harmonic is 20% (0.12/0.6) of the voltage of the second harmonic. The doubled reactance of the choke at the fourth harmonic halves the choke current, resulting in a fourth harmonic current that is only 10% of the second harmonic, so the approximation is fair, but there is room for improvement.

The sum of the AC currents drawn by each of the Fourier terms, up to and including the eighth harmonic, was investigated to find the maximum positive peak. (The negative peak is irrelevant since when added to the DC load current, it reduces the total peak current.) The result of this exercise modified the equation to:

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