{"id":4373,"date":"2012-09-26T08:15:09","date_gmt":"2012-09-26T15:15:09","guid":{"rendered":"http:\/\/rustybolt.info\/wordpress\/?p=4373"},"modified":"2012-10-06T13:29:53","modified_gmt":"2012-10-06T20:29:53","slug":"2012-09-26","status":"publish","type":"post","link":"https:\/\/rustybolt.info\/wordpress\/?p=4373","title":{"rendered":"2012-09-26 Joule Thief Works With The 2N3904 Backwards"},"content":{"rendered":"

I was observing this video<\/a>, and I saw that the 2N3904’s collector was connected to the negative and LED cathode, and the emitter was connected to the coil winding and LED anode.\u00a0 But I was surprised that when he connected it up, the LED lit up.\u00a0 Weird.\u00a0 But when he tried it with the 2n2222A (probably a PN2222A) backwards, it would not light.\u00a0 Which is what I had expected with the 2N3904.\u00a0 Apparently the 2N3904 had enough gain in the reverse direction to oscillate.\u00a0 But the emitter to base breakdown voltage is only 5 volts; fortunately the circuit stays below that maximum.<\/p>\n

Back to observing others experimenting (scary!)…<\/p>\n

Update Sep 28<\/strong> – TK has come up with another 18 minute video<\/a> which does further experiments with the transistors in forward and backward.\u00a0\u00a0 I like his test jig setup;\u00a0 he has everything glued down to a piece of veneer board, and everything stays put so it’s easy to make changes.\u00a0 However\u00a0 he could eliminate the current monitoring gizmo between the battery and holder.\u00a0 I think he has a double throw, center off switch.\u00a0 It would be easy to mount two #4 screws on the board to allow clipping on his current monitoring meter.\u00a0 Then switch the switch one way to monitor the current, the other way to bypass the current monitor.<\/p>\n

The problem is that during his experiment, the voltage on the depleted AA cell is changing.\u00a0 So it’s impossible to get an apples to apples comparison between the different configurations.\u00a0 I noticed that at one point in his readings the battery voltage was down to 0.76 volt, which is so low that the JT would have a hard time oscillating with the transistor in the correct way.\u00a0 I think it would be much better if he used a fresh battery with a stable 1.5 volts.\u00a0 Also it is wise to put a 10 uF or 22 uF capacitor across the battery leads to help eliminate any tendency to be unstable.<\/p>\n

Measuring power input is easy: just multiply the input voltage by the input current. \u00a0 But how do you measure power out?\u00a0 You put a 1 ohm resistor in series with the cathode of the LED.\u00a0 Then measure the voltage across this with the DMM set on 200 millivolts.\u00a0 Every millivolt will be equal to a milliamp, so 17 millivolts, for example will be 17 milliamps.\u00a0 Then take .017 amp (same as 17 millliamps)\u00a0 and multiply that by 3.3 volts, which is the assumed forward voltage of the white or blue LED.\u00a0 This will give you .0561 watt or 56.1 milliwatts.\u00a0 Divide that by the power in, then multiply by 100 to get the percent, and you have the efficiency.\u00a0 My Supercharged Joule Thief<\/a> \u00a0 has an efficiency of 70 to 90 percent.\u00a0 Since the 3.3 volts is assumed, this measurement is not entirely accurate , but it gives you a very good comparison of differences when you make a change to the circuit.\u00a0 If you want absolute accuracy, you should measure with the LED held a fixed distance away from a light meter inside of a dark enclosure, to shield it from ambient light.\u00a0 This will give you the actual light output.<\/p>\n

Maybe I should build a test jig like this.<\/p>\n

I had an earlier blog with the transistor in backwards<\/a>.<\/p>\n

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

I was observing this video, and I saw that the 2N3904’s collector was connected to the negative and LED cathode, and the emitter was connected to the coil winding and LED anode.\u00a0 But I was surprised that when he connected it up, the LED lit up.\u00a0 Weird.\u00a0 But when he tried it with the 2n2222A <\/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":[4,80],"tags":[],"class_list":["post-4373","post","type-post","status-publish","format-standard","hentry","category-joule-thief-smps-dc-dc","category-transistors"],"_links":{"self":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/4373","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=4373"}],"version-history":[{"count":12,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/4373\/revisions"}],"predecessor-version":[{"id":4381,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/4373\/revisions\/4381"}],"wp:attachment":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=4373"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=4373"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=4373"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}