|
A joule thief is a minimalist Armstrong〔("Fun Examples for Teaching Linear and Nonlinear Circuits" ), Circuits and Systems (ISCAS), 2013 IEEE International Symposium on, 19-23 May 2013, p2557 - 2560〕 self-oscillating voltage booster that is small, low-cost, and easy to build, typically used for driving light loads. It can use nearly all of the energy in a single-cell electric battery, even far below the voltage where other circuits consider the battery fully discharged (or "dead"); hence the name, which suggests the notion that the circuit is ''stealing'' energy or "joules" from the source. The term is a pun on the expression "jewel thief": one who steals jewelry or gemstones. The circuit is a variant of the blocking oscillator that forms an unregulated voltage boost converter. The output voltage is increased at the expense of higher current draw on the input, but the integrated (average) current of the output is lowered and brightness of a luminescence decreased. ==History== In the November 1999 issue of Everyday Practical Electronics (EPE) magazine, the "Ingenuity Unlimited" (reader ideas) section had a novel circuit idea entitled ''"One Volt LED - A Bright Light"'' by from Swindon, Wilts, UK. Three circuits examples were shown for operating LEDs from supply voltages below 1.5 Volts. The basic circuits consisted of a transformer-feedback ZTX450 NPN transistor voltage converter based on the blocking oscillator, which originally used a vacuum tube / thermionic valve and dates prior to World War II.〔Everday Practical Electronics; November 1999.〕 The name ''"Joule Thief"'' was coined by Clive Mitchell〔("Make a joule thief" ), www.bigclive.com, retrieved 28 June 2013〕 and given to his variant of Kaparnik's circuit which consisted of a single cell, a single BC549 NPN transistor, a coil with two windings, a single resistor (typically 1000 ohms), and a single white LED. Clive originally named the circuit ''"Vampire Torch"'', because it sucked the last remnants of life from a battery. Mitchell's newer circuit is essentially the same as Kaparnik's older circuit, except for component values. * The Kaparnik schematic showed a resistor value of 10K though he stated that lower resistance, such as 2K, would produce higher currents; where as Mitchell's schematic showed only a 1K resistor in his schematic. * Kaparnik stated that an NPN transistor with lower Vce(sat) yielded better results. He tested three transistors: ZTX450 at 73% efficiency, ZTX650 at 79% efficiency, BC550 at 57% efficiency. Mitchell showed only the BC549 in his schematic. 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「Joule thief」の詳細全文を読む スポンサード リンク
|