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The Pearson–Anson effect, discovered in 1922 by Stephen Oswald Pearson〔Stephen Oswald Pearson,''Dictionary of Wireless Technical Terms'' (London: Iliffe & Sons, 1926).〕 and Horatio Saint George Anson, is the phenomenon of an oscillating electric voltage produced by a neon bulb connected across a capacitor, when a direct current is applied through a resistor. This circuit, now called the Pearson-Anson oscillator, neon lamp oscillator, or sawtooth oscillator, is one of the simplest types of relaxation oscillator. It generates a sawtooth output waveform.〔 It has been used in low frequency applications such as blinking warning lights, stroboscopes,〔 tone generators in electronic organs〔 and other electronic music circuits, and in time bases and deflection circuits of early cathode ray tube oscilloscopes.〔 Since the development of microelectronics, these simple negative resistance oscillators have been superseded in many applications by more flexible semiconductor relaxation oscillators such as the 555 timer IC. ==Neon bulb as a switching device== A neon bulb, often used as an indicator lamp in appliances, consists of a glass bulb containing two electrodes, separated by an inert gas such as neon at low pressure. Its nonlinear current-voltage characteristics ''(diagram below)'' allow it to function as a switching device. When a voltage is applied across the electrodes, the gas conducts almost no electric current until a threshold voltage is reached ''(point b)'', called the ''firing'' or ''breakdown voltage'', ''V''b.〔〔( Dance, 1967 ), p.6-7〕 At this voltage electrons in the gas are accelerated to a high enough speed to knock other electrons off gas atoms, which go on to knock off more electrons in a chain reaction. The gas in the bulb ionizes, starting a glow discharge, and its resistance drops to a low value. In its conducting state the current through the bulb is limited only by the external circuit. The voltage across the bulb drops to a lower voltage called the ''maintaining voltage'' ''V''m. The bulb will continue to conduct current until the applied voltage drops below the ''extinction voltage'' ''V''e ''(point d)'', which is usually close to the maintaining voltage. Below this voltage, the current provides insufficient energy to keep the gas ionized, so the bulb switches back to its high resistance, nonconductive state ''(point a)''. The bulb's "turn on" voltage ''V''b is higher than its "turn off" voltage ''V''e. This property, called hysteresis, allows the bulb to function as an oscillator. Hysteresis is due to the bulb's negative resistance, the fall in voltage with increasing current after breakdown,〔〔 which is a property of all gas discharge lamps. Up until the 1960s sawtooth oscillators were also built with thyratrons. These were gas-filled triode electron tubes. These worked somewhat similarly to neon bulbs, the tube would not conduct until the cathode to anode voltage reached a breakdown voltage. The advantage of the thyratron was that the breakdown voltage could be controlled by the voltage on the grid.〔 This allowed the frequency of the oscillation to be changed electronically. Thyratron oscillators were used as time bases in oscilloscopes.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pearson–Anson effect」の詳細全文を読む スポンサード リンク
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