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<\/a>To enlarge, click more than once.<\/p><\/div>\n
I wound the two normal windings on the toroid core, then I wound a third winding of 20 turns for driving the LED. But instead of driving the LED directly from the transistor, I connected one of the 3rd winding leads to negative and the other lead to the anode of a 1N5817 Schottky diode. I connected the cathode of this diode to the positive of a 100 uF ‘lytic capacitor and connected its negative to the battery negative. In other words, the pulses from this winding are being rectified and filtered to DC. One important thing to remember is that this winding may give higher LED current when connected in one direction, so it’s best to try both directions and use the one with the highest LED current (see note).<\/p>\n
This DC is then connected directly to the LED. A 1 ohm resistor is between the LED cathode and the negative to allow the LED current to be measured: 1 millivolt equals 1 milliamp.<\/p>\n
The rest of the circuit is a conventional JT, but instead of a 1k resistor, I used two 27k resistors in series, totaling 54k. The transistor was a BC337-25. It used a standard 5mm white LED.<\/p>\n
The battery current measured about 23 mA, but when I put a short across the meter leads, I could see the LED get brighter, so I estimate the actual battery current is more like 27 mA. The meter read 8 millivolts across the 1 ohm resistor, so there are 8 milliamps through the LED. I calculated an efficiency of about 64 percent, which is a reasonable value for a Joule Thief.<\/p>\n
Note: Some experimenters try to solve this by using a diode bridge rectifier. but the bridge has two diode drops totaling 1.2 to 1.6 volts, which is up to half the power sent to the LED being wasted in the diodes as heat. Obviously this is not a good idea. Less diodes is best. Also using a Schottky diode with low voltage drop wastes less power.<\/p>\n","protected":false},"excerpt":{"rendered":"
I built this special Joule Thief a while ago, and I don’t remember if I wrote a blog about it. I wound the two normal windings on the toroid core, then I wound a third winding of 20 turns for driving the LED. But instead of driving the LED directly from the transistor, I connected <\/p>\n (Read More…)<\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4,12],"tags":[],"class_list":["post-10045","post","type-post","status-publish","format-standard","hentry","category-joule-thief-smps-dc-dc","category-led"],"_links":{"self":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/10045","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=10045"}],"version-history":[{"count":15,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/10045\/revisions"}],"predecessor-version":[{"id":10118,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/10045\/revisions\/10118"}],"wp:attachment":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=10045"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=10045"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=10045"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}