{"id":5346,"date":"2012-12-18T07:03:08","date_gmt":"2012-12-18T15:03:08","guid":{"rendered":"http:\/\/rustybolt.info\/wordpress\/?p=5346"},"modified":"2013-01-09T05:20:35","modified_gmt":"2013-01-09T13:20:35","slug":"2012-12-18-replication-of-any-value-joule-thief","status":"publish","type":"post","link":"https:\/\/rustybolt.info\/wordpress\/?p=5346","title":{"rendered":"2012-12-18 Replication of “Any Value Joule Thief”"},"content":{"rendered":"

\"\"<\/a>I watched this Youtube video<\/a> where he replicates a circuit from an Instructable on designing an “Any Value Joule Thief”<\/a>.\u00a0 I read the instructable, and found that the claims made by the author seemed far too optimistic.<\/p>\n

The Instructable goes through multiple calculations to arrive at values for the components in the schematic.\u00a0 In the video, he uses a 1.2V rechargeable battery and claimed that the circuit could put out hundreds of milliamps to a high power LED.<\/p>\n

I’d like to remind you that this two transistor V booster is not a true Joule Thief.\u00a0 In the picture, I show my replication of the circuit.\u00a0 I used PN2222A NPNs for both transistors.\u00a0 The other components are the same values that were given in the schematic.\u00a0 The big resistor on the right is the 1 ohm current sensing resistor used for measuring the current through the LED.\u00a0 The LED was a half watt 5 chip white 10mm LED capable of handling 150 milliamps.\u00a0 The 100 uH choke had a DC resistance of less than 1\/2 ohm.<\/p>\n

My results were as follows.\u00a0 I used a supply voltage of 1.5 volts, not 1.2 volts as shown in the schematics (this should increase the LED current, giving better results).\u00a0 The supply current was 160 mA, the LED current was 51 mA, and the frequency was 98 kHz.\u00a0 At 1.2 volts supply the LED current dropped down to about 42 milliamps.\u00a0 This is about half the LED current of the 2 transistor “JT” circuit<\/a> I blogged last week.<\/p>\n

I thought that it might help if I removed the 100 nF capacitor which was across the Q1 (the orange blob between the clip leads).\u00a0 I unsoldered it and the LED current jumped up to 74 mA at 1.5V, and the supply current increased to 290 mA, and the frequency jumped up to 216 kHz.\u00a0 I’m not sure what the reason was for using this capacitor.\u00a0 The 100 nF capacitor was damping the switching and slowing down the circuit.\u00a0 It obviously performed better without it.<\/p>\n

Instead of the 100 nF, I tried a 47 nF, but it still damped enough to dim the LED a bit.\u00a0 I then tried a 10 nF, and it dropped the frequency 40 kHz and the LED lost only 2 milliamps, from 76 to 74 mA.\u00a0 So a 10 nF is about the most that the circuit can handle without suffering too much.<\/p>\n

I tried a variable capacitor across the 68 pF capacitor.\u00a0 But no matter what setting it was, from 5 to 140 pF, the LED current went down as the capacitance was increased.\u00a0 So 68 pF or less may be the optimum value.<\/p>\n

The\u00a0 one thing I haven’t done is switch the output transistor.\u00a0 This PN2222A is capable of driving a regular 5mm white LED at full brightness.\u00a0 But when pressed to drive a high power LED, it cannot measure up to the task.\u00a0 It is quickly becoming apparent that the circuit has its limits just like others of this kind, and that no matter what calculations say, if the transistors are just average, the output to the LED will be just average.\u00a0 A good choice would be the transistor I used in the blog I linked to in\u00a0\u00b6 (paragraph) 4.<\/p>\n","protected":false},"excerpt":{"rendered":"

I watched this Youtube video where he replicates a circuit from an Instructable on designing an “Any Value Joule Thief”.\u00a0 I read the instructable, and found that the claims made by the author seemed far too optimistic. The Instructable goes through multiple calculations to arrive at values for the components in the schematic.\u00a0 In the <\/p>\n

(Read More…)<\/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-5346","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\/5346","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=5346"}],"version-history":[{"count":20,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/5346\/revisions"}],"predecessor-version":[{"id":5722,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/5346\/revisions\/5722"}],"wp:attachment":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=5346"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=5346"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=5346"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}