{"id":10920,"date":"2015-11-30T11:06:27","date_gmt":"2015-11-30T19:06:27","guid":{"rendered":"http:\/\/rustybolt.info\/wordpress\/?p=10920"},"modified":"2015-12-23T14:28:01","modified_gmt":"2015-12-23T22:28:01","slug":"2015-11-30-joule-thief-with-daylight-shutoff","status":"publish","type":"post","link":"https:\/\/rustybolt.info\/wordpress\/?p=10920","title":{"rendered":"2015-11-30 Low Power Joule Thief With Daylight Shutoff"},"content":{"rendered":"<p>This has been blogged, here and <a href=\"http:\/\/rustybolt.info\/wordpress\/?p=8234\">here<\/a>.\u00a0 I added a CdS photocell (resistor with a circle around it) to shut it off during daylight, thus conserving the AAA cell.\u00a0 I used a 100k resistor for the base bias, so it draws very low current from the cell.\u00a0 I can then call this a <u>low power Joule Thief<\/u>.<br \/>\n<a href=\"http:\/\/rustybolt.info\/wordpress\/wp-content\/uploads\/2015\/12\/wpid-wp-1449011537198.jpeg\"><img decoding=\"async\" title=\"wp-1449011537198\" class=\"alignnone size-full\"  alt=\"image\" src=\"http:\/\/rustybolt.info\/wordpress\/wp-content\/uploads\/2015\/12\/wpid-wp-1449011537198.jpeg\" \/><\/a> <\/p>\n<p>The T1 ferrite toroid core is 3\/8 inch or 9 mm O.D. with about twenty turns of 30 AWG wire for both the primary and secondary windings.  The 150 pF capacitor bypasses the secondary winding so the high value of the 100 k resistor doesn&#8217;t reduce the feedback.  The typical value for a Joule Thief is 1k.<\/p>\n<p>The &#8220;high energy&#8221; aka zinc carbon AAA battery I&#8217;m using has dropped below 1.25 volts, so it doesn&#8217;t have much life left.  The circuit has a lot of hysteresis.  The LED will stay on until the photocell gets well lit, then it will turn off.  Then to turn back on, the light has to get quite a bit dimmer than it was to turn off.  The hysteresis seems to be greater than when I started, possibly because the cell voltage has dropped.<\/p>\n<p>The transistor is S9014 D, which is similar to a 2N3904 or BC547, but the D on the end means it is very high gain, 600 to 1000.  This is why the LED is bright even though the base resistor is 100k.  A 2N3904 would put out less current to the LED with that resistor, or the resistor would have to be lowered to about 33k to get the same LED current.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>This has been blogged, here and here.\u00a0 I added a CdS photocell (resistor with a circle around it) to shut it off during daylight, thus conserving the AAA cell.\u00a0 I used a 100k resistor for the base bias, so it draws very low current from the cell.\u00a0 I can then call this a low power<a href=\"https:\/\/rustybolt.info\/wordpress\/?p=10920\"> <\/p>\n<p> (Read More&#8230;)<\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4,13],"tags":[],"class_list":["post-10920","post","type-post","status-publish","format-standard","hentry","category-joule-thief-smps-dc-dc","category-lighting"],"_links":{"self":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/10920","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=10920"}],"version-history":[{"count":10,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/10920\/revisions"}],"predecessor-version":[{"id":10948,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/10920\/revisions\/10948"}],"wp:attachment":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=10920"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=10920"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=10920"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}