{"id":64431,"date":"2025-05-12T09:18:28","date_gmt":"2025-05-12T06:18:28","guid":{"rendered":"https:\/\/wpcalc.com\/en\/?p=64431"},"modified":"2026-09-30T18:24:09","modified_gmt":"2026-09-30T15:24:09","slug":"lm317-current-regulator","status":"publish","type":"post","link":"https:\/\/wpcalc.com\/en\/engineering\/lm317-current-regulator\/","title":{"rendered":"LM317 Current Regulator Calculator"},"content":{"rendered":"<section class=\"not-prose calculator-box\" aria-labelledby=\"calculator-title\"><div class=\"flex items-baseline sm:items-center justify-between gap-2 sm:gap-3\"><div class=\"flex flex-col sm:flex-row sm:items-center gap-2\"><span class=\"icon icon-calculator text-primary-700! text-base! dark:text-primary-300!\" aria-hidden=\"true\"><\/span><h2 id=\"calculator-title\" class=\"text-lg font-display font-bold\">Constant Current Output from LM317<\/h2><\/div><div class=\"calcdash-favorite group\">\n  <button type=\"button\" class=\"favorite\" id=\"favorite\" data-favorite-id=\"64431\" data-favorite-title=\"LM317 Current Regulator\" data-favorite-url=\"https:\/\/wpcalc.com\/en\/engineering\/lm317-current-regulator\/\" data-favorite-excerpt=\"Calculate the output current of an LM317 constant current regulator from a single resistor value. Just enter the resistance between the output and adjust pins to get the current in amps.\" aria-label=\"Add to Favorites\" data-favorite-icon=\"icon icon-electrical\">\n    <span class=\"icon icon-shape-star-empty\" aria-hidden=\"true\"><\/span>\n  <\/button>\n  <div class=\"calcdash-favorite__tip\" aria-hidden=\"true\">\n   <span class=\"favorite-tooltip\" id=\"favorite-tooltip\"><\/span>\n  <\/div>\n  <span class=\"sr-only\" role=\"status\" id=\"favorite-status\"><\/span>\n<\/div><\/div><form action=\"https:\/\/wpcalc.com\/en\/engineering\/lm317-current-regulator\/\" method=\"POST\" class=\"calculator\" id=\"calculator-64431\" data-post=\"64431\"><fieldset class=\"fieldset-input is-1\"><legend class=\"sr-only\">Input Fields<\/legend><div class=\"field has-term\" id=\"input-1\"><label for=\"field-1\">Resistor value<\/label><div class=\"term\">R<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"text\" name=\"resistor_value\" id=\"field-1\" aria-describedby=\"calc-unit-1 calc-info-1\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" min=\"0.01\" value=\"10\"\/><div class=\"unit\" id=\"calc-unit-1\">\u03a9<\/div><small id=\"calc-info-1\">Resistor used to set constant current<\/small><\/div><\/fieldset><div class=\"buttons\"><button type=\"submit\" data-text=\"Re-Calculate\" id=\"calculate-button\" data-post=\"64431\">Calculate<\/button><button type=\"reset\">Reset<\/button><\/div><div class=\"field is-checkbox hidden!\" id=\"field-auto-calc\"><input type=\"checkbox\" id=\"auto-calc\"><label for=\"auto-calc\">Calculate automatically<\/label><small>If enabled, the result will update automatically when you change any value.<\/small><\/div><div class=\"fieldset-result is-hidden\" aria-labelledby=\"result-title\" aria-live=\"polite\" role=\"region\"> <h3 class=\"result-title bg-gradient-to-r from-primary-50 to-gray-50 dark:from-primary-900 dark:to-gray-800\" id=\"result-title\"><span class=\"icon icon-s-pulse\" aria-hidden=\"true\"><\/span> Your Results<\/h3><div class=\"result-box\"><div class=\"field-result\" id=\"output-1\"><span class=\"field-title\"><span>Output Current<\/span><\/span><span class=\"field-value\" id=\"result-1\" data-unit=\"A\"><\/span><button type=\"button\" class=\"copy-result\" data-tooltip=\"Copy Result\" aria-label=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\" aria-hidden=\"true\"><\/span><\/button><\/div><\/div><div class=\"result-actions\"><button type=\"button\" class=\"copy-link\"><svg viewBox=\"0 0 20 20\" fill=\"currentColor\" aria-hidden=\"true\"><path d=\"M12.232 4.232a2.5 2.5 0 0 1 3.536 3.536l-1.225 1.224a.75.75 0 0 0 1.061 1.06l1.224-1.224a4 4 0 0 0-5.656-5.656l-3 3a4 4 0 0 0 .225 5.865.75.75 0 0 0 .977-1.138 2.5 2.5 0 0 1-.142-3.667l3-3Z\"\/><path d=\"M11.603 7.963a.75.75 0 0 0-.977 1.138 2.5 2.5 0 0 1 .142 3.667l-3 3a2.5 2.5 0 0 1-3.536-3.536l1.225-1.224a.75.75 0 0 0-1.061-1.06l-1.224 1.224a4 4 0 1 0 5.656 5.656l3-3a4 4 0 0 0-.225-5.865Z\"\/><\/svg><span class=\"copy-link__text\">Copy link to this calculation<\/span><\/button><span class=\"sr-only\" role=\"status\" id=\"copy-link-status\"><\/span><\/div><\/div><a href=\"#respond\" class=\"hidden transition-opacity duration-300 opacity-0 w-50 text-sm justify-center items-center gap-2 px-4 py-2 rounded bg-gray-200 text-gray-700 hover:bg-gray-300\" id=\"leave-comment\"><span class=\"icon icon-comments\" aria-hidden=\"true\"><\/span>Leave a Comment<\/a><\/form><\/section><section id=\"calc-reactions\" class=\"not-prose hidden my-12 bg-gradient-to-r from-primary-50 to-gray-50 border border-indigo-100 rounded-xl px-6 py-4 shadow-sm\" data-post=\"64431\" aria-live=\"polite\" aria-labelledby=\"calc-reactions-title\"><p id=\"calc-reactions-title\" class=\"text-sm text-gray-500 text-center mb-2\">How did this result make you feel?<\/p><div role=\"group\" aria-labelledby=\"calc-reactions-title\" class=\"grid grid-cols-3 sm:flex sm:flex-row sm:justify-around gap-4 sm:items-center sm:flex-wrap\"><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"like\"><span class=\"reaction-count\" data-reaction-count=\"like\">1<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\ude00 <\/span><span class=\"reaction-description font-medium\">Like <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"helpful\"><span class=\"reaction-count\" data-reaction-count=\"helpful\">2<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\udca1 <\/span><span class=\"reaction-description font-medium\">Helpful <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"confused\"><span class=\"reaction-count\" data-reaction-count=\"confused\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\ude15 <\/span><span class=\"reaction-description font-medium\">Confused <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"disappointed\"><span class=\"reaction-count\" data-reaction-count=\"disappointed\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\ude1e <\/span><span class=\"reaction-description font-medium\">Disappointed <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"inaccurate\"><span class=\"reaction-count\" data-reaction-count=\"inaccurate\">0<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\u274c <\/span><span class=\"reaction-description font-medium\">Inaccurate <\/span><\/button><\/div><div id=\"reaction-message\" class=\"hidden mt-8 rounded-md border border-primary-100 bg-white\/50 backdrop-blur-sm px-4 py-2 text-sm text-center shadow-sm\"><\/div><\/section><div class=\"calcdash-ad not-prose calcdash-ad--calc_result calcdash-ad--in-article\"><ins class=\"adsbygoogle\" style=\"display:block\" data-ad-client=\"ca-pub-1721569815777345\" data-ad-slot=\"6317458308\" data-ad-layout=\"in-article\" data-ad-format=\"fluid\"><\/ins><script>(adsbygoogle = window.adsbygoogle || []).push({});<\/script><\/div>\n<style id=\"wpcoderpro-inline-1\">.formula-box {\r\n\tborder-bottom: none !important;\r\n}<\/style><section class=\"formula-box\" aria-labelledby=\"formula-title\">\r\n\t<div id=\"formula-title\" class=\"not-prose font-display mb-4\"><span class=\"icon icon-formula\" aria-hidden=\"true\"><\/span><h2>LM317 Current Regulator Formula<\/h2><\/div>\r\n\t<figure class=\"not-prose formula\">\r\n\t\t<figcaption class=\"formula-title\">Formula<\/figcaption>\r\n\t\t<div class=\"text-base text-gray-800\" id=\"formula\">\n\\[ I = \\frac{V_{ref}}{R} \\]\n<\/div>\r\n\t<\/figure>\r\n\t<\/p>\n<p><strong>Where:<\/strong><\/p>\n<ul>\n<li>\\(I\\) \u2014 output current (A)<\/li>\n<li>\\(V_{ref}\\) \u2014 LM317 reference voltage, nominally \\(1.25\\text{ V}\\)<\/li>\n<li>\\(R\\) \u2014 resistor connected between the output and adjust pins (\u03a9)<\/li>\n<\/ul>\n<p>The LM317 maintains a constant \\(1.25\\text{ V}\\) across the resistor, so the current flowing through it \u2014 and therefore through the load \u2014 is set entirely by the resistor value.<\/p>\n<p>\r\n<\/section>\n<style id=\"wpcoderpro-inline-459\">.calculation-box {\r\n\tborder-bottom: none !important;\r\n}<\/style><section id=\"calculation\" class=\"calculation-box\" aria-labelledby=\"calculation-title\">\r\n\t<div id=\"calculation-title\" class=\"not-prose font-display\"><span class=\"icon icon-unordered-list\" aria-hidden=\"true\"><\/span><h2>LM317 Current Regulator \u2013 Calculation Example<\/h2><\/div>\r\n\r\n<\/p>\n<p><strong>Example:<\/strong> a 10 \u03a9 resistor is connected between the output and adjust pins of an LM317 acting as a constant current source.<\/p>\n<p>\\[ I = \\frac{V_{ref}}{R} = \\frac{1.25}{10} = 0.125\\text{ A} \\]<\/p>\n<p><strong>Result:<\/strong> the regulator delivers a constant current of <strong>0.125 A (125 mA)<\/strong> to the load.<\/p>\n<p>\n\r\n<\/section>\n<h2>How to use the calculator<\/h2>\n<ol>\n<li>Enter the <strong>Resistor value<\/strong> in ohms (\u03a9). This is the resistor wired between the LM317 output pin and the adjust pin.<\/li>\n<li>The <strong>Output Current<\/strong> in amps (A) is displayed instantly, based on the LM317 reference voltage of 1.25 V.<\/li>\n<li>If you need a specific current instead, rearrange the formula as \\( R = \\frac{1.25}{I} \\), compute the required resistance, and enter it to verify.<\/li>\n<\/ol>\n<h2>What is an LM317 current regulator?<\/h2>\n<p>The LM317 is an adjustable linear voltage regulator, but with just one external resistor it becomes a simple and reliable <strong>constant current source<\/strong>. The resistor is connected between the output (OUT) and adjust (ADJ) pins, and the load is connected between the adjust pin and ground. Because the LM317 always keeps 1.25 V between its output and adjust pins, the current through the resistor is fixed at \\( I = 1.25\/R \\) \u2014 and since the adjust pin draws only a tiny current (about 50\u2013100 \u00b5A), essentially the same current flows through the load.<\/p>\n<p>This configuration is popular in <strong>LED drivers<\/strong>, where LEDs need a controlled current rather than a controlled voltage, and in <strong>battery chargers<\/strong> and current-limited test supplies, where exceeding a set current could damage the device being powered. The circuit requires only two components beyond the LM317 itself (the set resistor and, optionally, an input capacitor), which makes it one of the cheapest constant-current solutions available.<\/p>\n<p>Because the current depends only on a fixed reference voltage and a resistor \u2014 both stable over time and temperature \u2014 the output current stays constant even as the supply voltage or load resistance varies, as long as the LM317 has enough voltage headroom to operate (see the limitations below).<\/p>\n<h2>Resistor values for common currents<\/h2>\n<table>\n<thead>\n<tr>\n<th>Desired current<\/th>\n<th>Resistor value (\u03a9)<\/th>\n<th>Resistor power rating needed<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>20 mA<\/td>\n<td>62.5<\/td>\n<td>\u2265 0.05 W<\/td>\n<\/tr>\n<tr>\n<td>50 mA<\/td>\n<td>25<\/td>\n<td>\u2265 0.125 W<\/td>\n<\/tr>\n<tr>\n<td>100 mA<\/td>\n<td>12.5<\/td>\n<td>\u2265 0.25 W<\/td>\n<\/tr>\n<tr>\n<td>250 mA<\/td>\n<td>5<\/td>\n<td>\u2265 0.5 W<\/td>\n<\/tr>\n<tr>\n<td>500 mA<\/td>\n<td>2.5<\/td>\n<td>\u2265 1 W<\/td>\n<\/tr>\n<tr>\n<td>1 A<\/td>\n<td>1.25<\/td>\n<td>\u2265 2 W<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>The power dissipated by the resistor is \\( P = I^2 R = 1.25 \\times I \\); always choose a resistor with a rating comfortably above this value.<\/p>\n<h2>Limitations and practical tips<\/h2>\n<ul>\n<li><strong>Voltage headroom:<\/strong> the LM317 needs the input voltage to exceed the output voltage by at least 3 V (the drop-out voltage) plus the 1.25 V across the set resistor \u2014 about 4.25 V total in this configuration. Below that, the current will sag.<\/li>\n<li><strong>Power dissipation:<\/strong> the LM317 dissipates \\( P = (V_{in} - V_{load}) \\times I \\). At high currents or large input-output differences, use a heatsink. The TO-220 package can typically dissipate a few watts with adequate cooling.<\/li>\n<li><strong>Maximum ratings:<\/strong> the standard LM317 is limited to about 1.5 A output current and a 37 V input-output differential. For higher currents, use an LM338 (5 A) or LM350 (3 A), which work with the same formula.<\/li>\n<li><strong>Resistor tolerance:<\/strong> the output current accuracy is directly limited by the tolerance of the resistor and the 1.25 V reference (which varies slightly, typically 1.20\u20131.30 V between parts). Use a 1% resistor for precise currents.<\/li>\n<li><strong>Efficiency:<\/strong> as a linear regulator, excess voltage is converted to heat. For battery-powered or high-power LED applications, a switching constant-current driver may be more efficient.<\/li>\n<\/ul>\n<p>When choosing wiring for your circuit, check that the conductor size can handle the current with our <a href=\"https:\/\/wpcalc.com\/en\/engineering\/wire-gauge\/\">Wire Gauge calculator<\/a>. If you need to build the set resistor from available parts, the <a href=\"https:\/\/wpcalc.com\/en\/engineering\/parallel-resistance\/\">Parallel Resistance calculator<\/a> helps combine resistors to reach the exact value. For voltage-regulation applications with a similar discrete design, see the <a href=\"https:\/\/wpcalc.com\/en\/engineering\/zener-diode\/\">Zener Diode Resistor calculator<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Calculate the output current of an LM317 constant current regulator from a single resistor value. Just enter the resistance between the output and adjust pins to get the current in amps.<\/p>\n","protected":false},"author":70,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[4],"tags":[94],"class_list":["post-64431","post","type-post","status-publish","format-standard","hentry","category-engineering","tag-circuits"],"acf":[],"_links":{"self":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/64431","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/users\/70"}],"replies":[{"embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/comments?post=64431"}],"version-history":[{"count":3,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/64431\/revisions"}],"predecessor-version":[{"id":65983,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/64431\/revisions\/65983"}],"wp:attachment":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/media?parent=64431"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/categories?post=64431"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/tags?post=64431"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}