Apparatus for operating electric discharge lamps

Claim 2

In apparatus for operating an electric discharge lamp comprising an electric power source, a first semiconductor switching and a reactive impedance element and a discharge lamp which are connected in series across said source, a second semiconductor switching element connected in parallel with the series connection of said reactive impedance element and said discharge lamp, and a control circuit operating said discharge lamp at high frequency by generating two pulse sequences for alternately switching on said first and second semiconductor elements, the improvement wherein said control circuit includes means for providing a time interval greater than the turn-off time of said first and second semiconductor switching elements between pulses of two pulse sequences for alternately switching on said first and second semiconductor switching elements.

Claim 3

An apparatus as claimed in claim 1 wherein said first and second semiconductor switching elements are both transistors.

Claim 4

An apparatus as claimed in claim 1 wherein said first and second semiconductor elements are both thyristors.

Claim 5

An apparatus as claimed in claim 1 wherein said control circuit comprises an astable multivibrator for generating two pulse sequences different by 180* in phase, a first and a second differentiating means receiving two pulse sequences respectively from said astable multivibrator and deriving differentiated pulses, a first and a second monostable multivibrator for generating in synchronism with said differentiated pulses two pulse sequences of pulses having a pulse width smaller than that of pulses from said astable multivibrator and thereby providing a time interval greater than the turn-off time of said semiconductor switching elements between pulses of two pulse sequences, a first and a second means for amplifying each pulse sequence from said first and second monostable multivibrator, and a first and a second transformer for supplying each amplified pulse sequence from said first and second amplifying means respectively to said first and second semiconductor switching elements.

Claim 6

An apparatus as claimed in claim 1 wherein said control circuit comprises an astable multivibrator, a flip-flop for receiving an output pulse sequence from said astable multivibrator and generating two pulse sequences different by 180* in phase, a first and a second AND means receiving respectively one of said two pulse sequences and further respectively receiving output pulse from said astable multivibrator to derive two pulse sequences equal in pulse width to the pulse from said astable multivibrator thereby imparting a time interval longer than the turn-off time of said semiconductor switching elements between pulses of the two pulse sequences, a first and a second amplifying means for amplifying output pulse sequences from said first and second AND means, and a first and second transformer for impressing amplified pulse sequences respectively on said first and second semiconductor switching elements.

Claim 7

An apparatus as claimed in claim 1 wherein said control circuit comprises an astable multivibrator for generating pulse sequence having a positive and a negative voltage level, an integrating means for integrating the output pulse sequence from said astable multivibrator, a Schmitt circuit having threshold levels substantially symmetric in positive and negative portions and for shaping the output from said integrating means for obtaining a rectangular pulse having a predetermined positive voltage leveL and a rectangular pulse having a predetermined negative voltage level, a first rectifying means for taking out only pulses having positive voltage level from said Schmitt circuit, a second rectifying means for taking out only pulses having negative voltage level, means for reversing the polarity of negative pulses from said second rectifying means, a first and a second amplifying means for amplifying the output pulse respectively from said reversing means and said first rectifying means, and a first and a second transformer for supplying the output pulses from said first and second amplifying means to said first and second semiconductor switching elements.

Claim 8

An apparatus as claimed in claim 1 wherein said control circuit comprises a sine wave oscillator, a first rectifying means for deriving only portions of positive polarity from the output of said sine wave oscillator, a second rectifying means for deriving only portions of negative polarity, means for reversing the output from said second rectifying means, a first and a second Schmitt circuit having predetermined threshold levels for shaping the outputs respectively from said reversing means and said first rectifying means, a first and a second amplifying means for amplifying the outputs respectively of said first and second Schmitt circuits, and a first and a second transformer for supplying the output pulses from said first and second amplifying means respectively to said first and second semiconductor switching elements.