{"id":4105,"date":"2012-09-10T07:30:13","date_gmt":"2012-09-10T14:30:13","guid":{"rendered":"http:\/\/rustybolt.info\/wordpress\/?p=4105"},"modified":"2012-12-18T07:04:32","modified_gmt":"2012-12-18T15:04:32","slug":"2012-09-10","status":"publish","type":"post","link":"https:\/\/rustybolt.info\/wordpress\/?p=4105","title":{"rendered":"2012-09-10 Hybrid Ge – Si Joule Thief"},"content":{"rendered":"

\"\"<\/a>I’ve been running some AA and AAA cells on a few Joule Thiefs that use silicon transistors until the cell gets down to about a half volt, then I switch the cell to a germanium Joule Thief and run it until the LED goes out and there’s typically less than a quarter volt left in the cell.\u00a0 Some of the AA and AAA cells are way, way out of date, like the 1990s and even a few from the late ’80s.\u00a0 Believe it or not, these still have enough juice in them to light up a JT fairly bright.\u00a0 But I’ve had some of them leak, so I decided I have to get rid of them, so why not run some JTs while I’m getting rid of them?<\/p>\n

The solution to the leakage problem is to use a pair of small magnets to hold the wires on to the ends of the cell.\u00a0 If it leaks, the corrosion only affects the small magnets and usually can be scraped off the magnet so it can be reused.<\/p>\n

But I wanted to get rid of having to switch from silicon to germanium Joule Thiefs.\u00a0 Why not combine them into one?\u00a0 Good idea.<\/p>\n

I decided that an easy way to do this is to parallel one of each transistor. \u00a0 If the germanium is a PNP, then I’ll have to use a PNP silicon such as the 2N4403 or BC327.\u00a0 The emitters and collectors of both Si and Ge transistors are connected together.\u00a0 The existing 1k resistor to the silicon is still used, and another 1k resistor is connected to the second transistor’s base and the winding lead that’s going to the original 1k.\u00a0 See the attached photo.\u00a0 The BC327 silicon transistor (black plastic case) is nestled between the leads of the 2N404 germanium transistor ( larger metal case).<\/p>\n

Downshift<\/strong> – When the cell has more than a half volt left, the silicon and germanium transistors will both switch current to the coil.\u00a0 As the cell voltage drops below 1\/2 volt, the silicon stops working, and the germanium continues to switch current until the cell voltage drops below a quarter volt.\u00a0\u00a0 Then both transistors stop, and the cell is thoroughly drained and ready for the trash can.<\/p>\n

Also, the germanium transistor will start up with 1\/4 volt from the cell, and the silicon transistor will then go along for the ride, idling in the background.\u00a0 The two transistors should give more current to the LED than a single transistor, but I haven’t measured the LED current yet.<\/p>\n

I’ll have to convert a couple of the JTs I’m using and see how it works.\u00a0 Well, I’ve already done that, as evidenced by the mess of wires in the photo.\u00a0 I have some germanium transistors that are NPN so I won’t have to switch the polarity of the JT.<\/p>\n

Another thought<\/strong> – I could add a third winding to the coil and put it in series with the existing feedback winding.\u00a0 The idea is the germanium transistor using the existing feedback winding would get the JT running when the cell voltage is less than 1\/2 volt, and the added winding would boost the voltage to get the silicon transistor conducting even though the cell voltage is low.\u00a0 Another thought: use this added winding to drive the gate of a 2N7000 MOSFET, and see if the two transistors will run at very low cell voltages.\u00a0 Also, if the winding was isolated it could be rectified, filtered and the DC used to provide a several volt supply to drive the gate of a larger MOSFET.\u00a0 Essentially the idea here is to use the germanium transistor just for minimal current generation for supplying the higher voltage the\u00a0 larger switching transistor needs.\u00a0 But I have to remember that I have already done a similar thing<\/a> with regular silicon transistors.<\/p>\n

I did a few tests with ‘dead’ batteries.\u00a0 It works, giving a lot less light when the cell is below a half volt, but it drains the cell, which is my main objective.<\/p>\n

Back to experimenting…<\/p>\n","protected":false},"excerpt":{"rendered":"

I’ve been running some AA and AAA cells on a few Joule Thiefs that use silicon transistors until the cell gets down to about a half volt, then I switch the cell to a germanium Joule Thief and run it until the LED goes out and there’s typically less than a quarter volt left in <\/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-4105","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\/4105","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=4105"}],"version-history":[{"count":16,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/4105\/revisions"}],"predecessor-version":[{"id":5348,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/4105\/revisions\/5348"}],"wp:attachment":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=4105"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=4105"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=4105"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}