Pulse-width-modulation and the Baxandall Class-D oscillator

Jun 23, 2006 21 Replies

There's a hint on page 232, in reference to the L-C network for driving fluorescent tubes.... "the characteristic frequency is made approximately equal to the operating frequency and the network operates as a Boucherot network, giving a constant current output for a constant voltage input.

.... and then in a paper for a high power inverter from the Daresbury Laboratory.

Precis below.

L Vs---)))))---+-----+ | \\|/ I-load | \\ C=== / R-load | \\ | | -------------+-----+

"When driven by a sinusoidal voltage voltage (Vs) at the resonant frequency it has the property that the current in the load is given by:-

Iload = Vs/j.2pi.f.L.

ie, I-load is independant of the load value, making the circuit a natural constant current source."

Ref [4] P. Boucherot, "Concerning systems in which V1/I2 is constant". Revue Generale de l'Electricite, Vol 5, page 203. 1919.

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There are also audio references to the Boucherot Cell, which is the series R+C network placed on the output of amps to stabilise them. If the network acquires an inductance it gets called a Zobel Network.

Tony Williams.

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