{"id":5450,"date":"2012-12-20T13:11:17","date_gmt":"2012-12-20T21:11:17","guid":{"rendered":"http:\/\/rustybolt.info\/wordpress\/?p=5450"},"modified":"2013-01-09T05:19:00","modified_gmt":"2013-01-09T13:19:00","slug":"2012-12-22-joule-thief-no-good-for-flasher","status":"publish","type":"post","link":"https:\/\/rustybolt.info\/wordpress\/?p=5450","title":{"rendered":"2012-12-22 Joule Thief No Good For Flasher"},"content":{"rendered":"

\"\"<\/a><\/p>\n

Update:<\/strong> This circuit is much like the Supercharged JT, see the end.<\/p>\n

A while back I built a Joule Thief flasher, like the one I had seen somewhere on the web, most likely on Youtube.\u00a0 The schematic shows the different arrangement of the feedback winding and base bias resistor.\u00a0 Normally the feedback winding is in series with the 1k resistor to the positive supply.\u00a0 But in this arrangement, one lead of the feedback winding is connected to negative, and the other lead is connected to the timing capacitor.\u00a0 In my first build, I had used a 120k ohm resistor for the base bias from positive to the base, and a 33 uF ‘lytic for the timing capacitor, but the flashes were so fast that I had to put another 220 uF capacitor across the 33 uF.\u00a0 Even with this large capacitor, the flash rate was still too fast.\u00a0 And the flash was very weak, not really visible.\u00a0 The supply current was very low, only a milliamp or less.<\/p>\n

So at this time, I decided that if I was going to use an even bigger timing capacitor, I would have to use a smaller timing resistor to give the transistor more base bias and help brighten the LED (I used an amber LED).\u00a0 I put a 33k resistor across the 120k, which was then effectively 25.8 k.\u00a0 The flash rate sped up, but the LED didn’t get much brighter.\u00a0 And at this time, I figured that if I lowered the timing resistor down to where the flash was much brighter, the timing capacitor would have to be a thousand microfarads or more.\u00a0 Nix to that!\u00a0 My Supercharged Joule Thief Flasher does a much better job with a capacitor of a few uF.<\/p>\n

So now what should I do?\u00a0 I’ll change it back to a Joule Thief, but I will just leave it like it is, with the feedback winding to negative.\u00a0 So I removed the capacitor and put a 0.1 uF capacitor in its place.\u00a0 Well, of course the flash rate sped up so fast that the LED looked continuously on to my eye.\u00a0 But it was still too dim.\u00a0 The frequency was 4567 kHz.<\/p>\n

I removed the 0.1 uF capacitor and put a .01 uF capacitor in its place.\u00a0 The LED was brighter and the narrow pulses were getting closer together, as I saw them on my ‘scope.\u00a0 With the scope on the collector, the waveform was a narrow low positive voltage spike, followed by a much more negative voltage spike.\u00a0\u00a0 The frequency was 46 kHz, but there was still a lot of ‘dead time’ between spikes.\u00a0 I figured that if I decreased the timing capacitor even further, the spikes would get even closer together and less dead time would mean a brighter LED.\u00a0 So I replaced the .01 uF with a .001 uF or 1 nF.\u00a0 The LED became brighter and the spikes were closer together.<\/p>\n

Well, I figured that the spikes needed to be a bit closer, so I changed the timing capacitor to a 330 pF.\u00a0 Now the LED was getting bright enough to see decently and the pulses were close together.\u00a0 The frequency was 172 kHz. \u00a0 Even so, the supply current was only 5 mA, which is less than a tenth of a normal Joule Thief.<\/p>\n

Conclusion<\/h3>\n

Right now, I can say from this experience that this circuit the way it is, is not the optimum for a Joule Thief, and that it is definitely no good for a flasher, even though the circuit does flash dimly.\u00a0 I will try to increase the base bias current by reducing the value of the resistor below 33k in parallel with 120k.<\/p>\n

I have changed R1 to a 5.6k resistor, which was the value that gave about 50 milliamps supply current.\u00a0 The amber LED brightened considerably.\u00a0 I put a 0.47 ohm resistor in series with the LED so I could measure the LED current.\u00a0 The LED current was maxed at 15.5 milliamps when I changed the capacitor to a variable capacitor and tuned it to 101 pF.\u00a0 So I replaced it with a 100 pF disk capacitor. The frequency was almost 300 kHz and the supply current at 1.5V was about 50 milliamps.\u00a0 That was very low for a current of 25.5 mA through the amber LED.<\/p>\n

The amber LED was brightest when the variable capacitor was broadly tuned to a certain point.\u00a0 This is much like the Supercharged Joule Thief, where the capacitor interacts with the coil’s feedback winding to give higher efficiency than a conventional Joule Thief.<\/p>\n

I removed the amber LED and replaced it with a white LED.\u00a0 This is so I can make an “apples to apples”comparison with the Supercharged JT.\u00a0 I further reduced the R1 to 3.9k, to increase the supply current up to the point where the Supercharged JT usually is.\u00a0 I was getting about 15 mA to the LED with a supply current of 48 mA.\u00a0 The frequency was 593kHz which is very high, at the bottom of the AM broadcast band.\u00a0 Some figures for calculating the efficiency:<\/p>\n

3.3V * 0.015A = .0495 W or 49.5 milliwatts.<\/p>\n

1.5V * .048A = .072W or 72 milliwatts.<\/p>\n

49.5 \/ 72 = 68.75 percent.<\/p>\n

So this circuit is on the very high end of efficiency of the conventional JT, but on the low end of the efficiency of the Supercharged JT.\u00a0 I will have to make another one or two of these to see if the circuit is consistent with the parts I used.<\/p>\n

I’m building a second one, so read my blog about it here<\/strong><\/a>.<\/p>\n

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

Update: This circuit is much like the Supercharged JT, see the end. A while back I built a Joule Thief flasher, like the one I had seen somewhere on the web, most likely on Youtube.\u00a0 The schematic shows the different arrangement of the feedback winding and base bias resistor.\u00a0 Normally the feedback winding is 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-5450","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\/5450","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=5450"}],"version-history":[{"count":23,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/5450\/revisions"}],"predecessor-version":[{"id":5719,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/5450\/revisions\/5719"}],"wp:attachment":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=5450"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=5450"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=5450"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}