{"id":262,"date":"2015-01-11T20:49:35","date_gmt":"2015-01-11T20:49:35","guid":{"rendered":"http:\/\/transistorgrab.de\/?p=262"},"modified":"2016-08-06T10:58:27","modified_gmt":"2016-08-06T10:58:27","slug":"tiny-led-booster","status":"publish","type":"post","link":"https:\/\/transistorgrab.de\/en\/2015\/01\/11\/tiny-led-booster\/","title":{"rendered":"Tiny LED booster"},"content":{"rendered":"<p>I own an older head-lamp (one that has a rubber band which you wear on your head) that still operated with a light bulb.<\/p>\n<p>But LED technology has made impressive progress in recent years and therefore I had the idea to transform this lamp to a LED light source.<\/p>\n<p><!--more--><\/p>\n<p>From\u00a0<a href=\"http:\/\/www.ti.com\/\">TI<\/a>\u00a0there is a device LM2731 in a compact SOT-23 package.<\/p>\n<p><a href=\"https:\/\/i0.wp.com\/transistorgrab.de\/wp-content\/uploads\/2015\/01\/schematic_original.png\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" style=\"background-image: none; float: none; padding-top: 0px; padding-left: 0px; margin-left: auto; display: block; padding-right: 0px; margin-right: auto; border: 0px;\" title=\"schematic_original\" src=\"https:\/\/i0.wp.com\/transistorgrab.de\/wp-content\/uploads\/2015\/01\/schematic_original_thumb.png?resize=437%2C199\" alt=\"schematic_original\" width=\"437\" height=\"199\" border=\"0\" \/><\/a><\/p>\n<p>The standard application (see above) is quite usable for LED applications with only a small modification.<\/p>\n<p>The LED needs to be connected between the output diode (D102) and the feedback input (pin 3). A resistor between the feedback pin and ground then defines the LED current.<\/p>\n<p>The resistor value is calculated from the desired LED current and the feedback voltage of 1.23 V.<br \/>\nWith a LED current of 25 mA the resistor value results in <code>1.23 V\/0.025 A = 49.2 \u03a9.<\/code><\/p>\n<p>A higher value reduces the LED current, a lower value increases it.<\/p>\n<p>This modification does not care about the number of LEDs connected in series because only the current through the sense-resistor controls the output voltage. The LM2731 can generate up to 22 V output voltage and therefore drive up to 6 white LED in a single string.<\/p>\n<p><span style=\"line-height: 1.5;\">Coil L102 needs to be modified accordingly, naturally.<\/span><\/p>\n<p>Of you want to protect the circuit against an interruption in the LED string (and therefore producing a too high output voltage) you can attach a resistor parallel to the LED (string) directly on the board (example value 890\u00a0\u03a9 when using a 50\u00a0\u03a9 sense resistor).<\/p>\n<p><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" style=\"background-image: none; float: none; padding-top: 0px; padding-left: 0px; margin-left: auto; display: block; padding-right: 0px; margin-right: auto; border: 0px;\" title=\"schematic_mod\" src=\"https:\/\/i0.wp.com\/transistorgrab.de\/wp-content\/uploads\/2015\/01\/schematic_mod.png?resize=437%2C216\" alt=\"schematic_mod\" width=\"437\" height=\"216\" border=\"0\" \/><\/p>\n<p><a href=\"https:\/\/i0.wp.com\/transistorgrab.de\/wp-content\/uploads\/2015\/01\/DSC_0069.jpg\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" style=\"background-image: none; float: none; padding-top: 0px; padding-left: 0px; margin-left: auto; display: block; padding-right: 0px; margin-right: auto; border: 0px;\" title=\"DSC_0069\" src=\"https:\/\/i0.wp.com\/transistorgrab.de\/wp-content\/uploads\/2015\/01\/DSC_0069_thumb.jpg?resize=436%2C772\" alt=\"DSC_0069\" width=\"436\" height=\"772\" border=\"0\" \/><\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>I own an older head-lamp (one that has a rubber band which you wear on your head) that still operated with a light bulb. But LED technology has made impressive progress in recent years and therefore I had the idea to transform this lamp to a LED light source.<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[1],"tags":[72,69,71,17,70],"class_list":["post-262","post","type-post","status-publish","format-standard","hentry","category-allgemeines","tag-led","tag-power-supply","tag-schaltregler","tag-spannungsquellen","tag-switching-power-supply"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p8KIDw-4e","jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/transistorgrab.de\/en\/wp-json\/wp\/v2\/posts\/262","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/transistorgrab.de\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/transistorgrab.de\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/transistorgrab.de\/en\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/transistorgrab.de\/en\/wp-json\/wp\/v2\/comments?post=262"}],"version-history":[{"count":0,"href":"https:\/\/transistorgrab.de\/en\/wp-json\/wp\/v2\/posts\/262\/revisions"}],"wp:attachment":[{"href":"https:\/\/transistorgrab.de\/en\/wp-json\/wp\/v2\/media?parent=262"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/transistorgrab.de\/en\/wp-json\/wp\/v2\/categories?post=262"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/transistorgrab.de\/en\/wp-json\/wp\/v2\/tags?post=262"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}