{"id":4815,"date":"2012-10-28T19:04:48","date_gmt":"2012-10-29T02:04:48","guid":{"rendered":"http:\/\/rustybolt.info\/wordpress\/?p=4815"},"modified":"2012-11-08T06:43:54","modified_gmt":"2012-11-08T14:43:54","slug":"2012-10-28","status":"publish","type":"post","link":"https:\/\/rustybolt.info\/wordpress\/?p=4815","title":{"rendered":"2012-10-28 Joule Thief Circuit From 1960"},"content":{"rendered":"<p><a href=\"http:\/\/rustybolt.info\/wordpress\/?attachment_id=4892\" rel=\"attachment wp-att-4892\"><img loading=\"lazy\" decoding=\"async\" class=\"alignright size-medium wp-image-4892\" title=\"DSC_0045S\" src=\"http:\/\/rustybolt.info\/wordpress\/wp-content\/uploads\/2012\/10\/DSC_0045S-229x300.jpg\" alt=\"\" width=\"229\" height=\"300\" srcset=\"https:\/\/rustybolt.info\/wordpress\/wp-content\/uploads\/2012\/10\/DSC_0045S-229x300.jpg 229w, https:\/\/rustybolt.info\/wordpress\/wp-content\/uploads\/2012\/10\/DSC_0045S.jpg 784w\" sizes=\"auto, (max-width: 229px) 100vw, 229px\" \/><\/a>I took a picture of this old application note from Texzs Instruments dated 1960.\u00a0 The circuit uses a germanium transistor, and adds a third winding to the coil to get high voltage (800 volts).\u00a0 If this third winding is removed and a LED is placed across the Q1 collector and emitter, and the supply voltage is reduced to less than the LED V, then it would be essentially a Joule Thief.<\/p>\n<p>They used two resistors in a voltage divider to give the transistor base bias current.\u00a0 One thing that we should remember is that the germanium transistor could have an emitter to base reverse breakdown voltage as high as the collector breakdown voltage.\u00a0 Today\u2019s silicon transistors are typically rated for 5 or 6 volts, not any higher.\u00a0 This is not a problem when the supply voltage is only a volt or two, but if the supply voltage goes above 5V, then the circuit could put the same negative voltage on the base, so the transistor must have some way to protect it from excessive reverse E to B voltage.\u00a0 The ratio between the windings can be changed so that the feedback winding gets a reduced negative voltage.\u00a0 Or a few diodes or LED can be put between emitter and base to shunt excessive voltages.\u00a0 However this wastes some power, which is not desirable with a battery operated circuit.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>I took a picture of this old application note from Texzs Instruments dated 1960.\u00a0 The circuit uses a germanium transistor, and adds a third winding to the coil to get high voltage (800 volts).\u00a0 If this third winding is removed and a LED is placed across the Q1 collector and emitter, and the supply voltage<a href=\"https:\/\/rustybolt.info\/wordpress\/?p=4815\"> <\/p>\n<p> (Read More&#8230;)<\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4],"tags":[],"class_list":["post-4815","post","type-post","status-publish","format-standard","hentry","category-joule-thief-smps-dc-dc"],"_links":{"self":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/4815","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=4815"}],"version-history":[{"count":9,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/4815\/revisions"}],"predecessor-version":[{"id":4893,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/4815\/revisions\/4893"}],"wp:attachment":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=4815"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=4815"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=4815"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}