LED Driver LM3409 | Forum for Electronics

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It may not display this or other websites correctly.<br />You should upgrade or use an <a href="https://www.google.com/chrome/" target="_blank" rel="noopener">alternative browser</a>.</div> <div class="p-body-header"> <div class="p-title "> <h1 class="p-title-value">LED Driver LM3409</h1> </div> <div class="p-description"> <ul class="listInline listInline--bullet"> <li> <i class="fa--xf fal fa-user" aria-hidden="true" title="Thread starter"></i> <span class="u-srOnly">Thread starter</span> <a href="/members/abi0987654321.694292/" class="username u-concealed" dir="auto" data-user-id="694292" data-xf-init="member-tooltip">abi0987654321</a> </li> <li> <i class="fa--xf fal fa-clock" aria-hidden="true" title="Start date"></i> <span class="u-srOnly">Start date</span> <a href="/threads/led-driver-lm3409.414072/" class="u-concealed"><time class="u-dt" dir="auto" datetime="2025-02-18T08:48:07+0000" data-time="1739868487" data-date-string="Feb 18, 2025" data-time-string="8:48 AM" title="Feb 18, 2025 at 8:48 AM">Today at 8:48 AM</time></a> </li> </ul> </div> </div> <div class="p-body-main p-body-main--withSidebar "> <div class="p-body-contentCol"></div> <div class="p-body-sidebarCol"></div> <div class="p-body-content">  <div id='div-gpt-eda_wallpaper'> <script> googletag.cmd.push(function() { googletag.display('div-gpt-eda_wallpaper'); }); </script> </div> <div class="p-body-pageContent"> <div class="block block--messages " data-xf-init="lightbox select-to-quote" data-message-selector=".js-post" data-lb-id="thread-414072"> <div class="block-outer"></div> <div class="block-outer js-threadStatusField"></div> <div class="block-container"> <div class="block-body"> <article class="message message--post js-post js-inlineModContainer " data-author="abi0987654321" data-content="post-1788887" id="js-post-1788887" > <span class="u-anchorTarget" id="post-1788887"></span> <div class="message-header"> <header class="message-attribution message-attribution--split"> <ul class="message-attribution-main listInline "> <li class="u-concealed"> <a href="/threads/led-driver-lm3409.414072/post-1788887" rel="nofollow" > <time class="u-dt" dir="auto" datetime="2025-02-18T08:48:07+0000" data-time="1739868487" data-date-string="Feb 18, 2025" data-time-string="8:48 AM" title="Feb 18, 2025 at 8:48 AM">Today at 8:48 AM</time> </a> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <a href="/threads/led-driver-lm3409.414072/post-1788887" class="message-attribution-gadget" data-xf-init="share-tooltip" data-href="/posts/1788887/share" aria-label="Share" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </a> </li> <li> <a href="/threads/led-driver-lm3409.414072/post-1788887" rel="nofollow"> #1 </a> </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" > <div class="message-avatar "> <div class="message-avatar-wrapper"> <a href="/members/abi0987654321.694292/" class="avatar avatar--m avatar--default avatar--default--dynamic" data-user-id="694292" data-xf-init="member-tooltip" style="background-color: #521433; color: #d1478c"> <span class="avatar-u694292-m" role="img" aria-label="abi0987654321">A</span> </a> </div> </div> <div class="message-userDetails"> <h4 class="message-name"><a href="/members/abi0987654321.694292/" class="username " dir="auto" data-user-id="694292" data-xf-init="member-tooltip">abi0987654321</a></h4> <h5 class="userTitle message-userTitle" dir="auto">Newbie</h5> </div> <img src="/styles/images/ranks/blevel1.gif" alt="Newbie level 4"> <div class="message-userExtras"> <dl class="pairs pairs--justified joinedBlock"> <dt>Joined</dt> <dd>Feb 18, 2025</dd> </dl> <dl class="pairs pairs--justified pairs--xbBoxed"> <dt>Messages</dt> <dd>6</dd> </dl> <dl class="pairs pairs--justified"> <dt> Helped</dt> <dd>0</dd> </dl> <dl class="pairs pairs--justified"> <dt>Reputation </dt> <dd> <a href="/reputation/authors/abi0987654321.694292" class="fauxBlockLink-linkRow u-concealed">0</a> </dd> </dl> <dl class="pairs pairs--justified"> <dt>Reaction score</dt> <dd>0</dd> </dl> <dl class="pairs pairs--justified pairs--xbBoxed trophyBlock"> <dt>Trophy points</dt> <dd>1</dd> </dl> <dl class="pairs pairs--justified creditBlock"> <dt title="Activity points">Activity points</dt> <dd> <a href="/activity/" data-xf-click="overlay" class="fauxBlockLink-blockLink u-concealed"> 34 </a> </dd> </dl> </div> <span class="message-userArrow"></span> </section> </div> <div class="message-cell message-cell--main"> <div class="message-main js-quickEditTarget"> <div class="message-content js-messageContent"> <div class="message-userContent lbContainer js-lbContainer " data-lb-id="post-1788887" data-lb-caption-desc="abi0987654321 · Feb 18, 2025 at 8:48 AM"> <article class="message-body js-selectToQuote"> <div > <div class="bbWrapper">I am having doubt on peak current control circuit (Rsns) section. Since op-Amp can ref voltage with ground. In that case voltage at non-inverting terminal should be 1.24v. How it is Vcst= 2.48mV? How Vcst=248mV will be the ref voltage to the comparartor? How did they derive Vcst=238mV? In what basic principle is used in that circuit analysis?<br /> <br /> <br /> Page N0=12<br /> <br /> This is the circuit</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> <section class="message-attachments"> <h4 class="block-textHeader">Attachments</h4> <ul class="attachmentList"> <li class="file file--linked"> <a class="u-anchorTarget" id="attachment-197411"></a> <script class="js-extraPhrases" type="application/json"> { "lightbox_close": "Close", "lightbox_next": "Next", "lightbox_previous": "Previous", "lightbox_error": "The requested content cannot be loaded. 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7</h5> </div> <img src="/styles/images/ranks/hlevel4.gif" alt="Advanced Member level 7"> <div class="message-userExtras"> <dl class="pairs pairs--justified joinedBlock"> <dt>Joined</dt> <dd>Apr 17, 2014</dd> </dl> <dl class="pairs pairs--justified pairs--xbBoxed"> <dt>Messages</dt> <dd>26,534</dd> </dl> <dl class="pairs pairs--justified"> <dt> Helped</dt> <dd>4,933</dd> </dl> <dl class="pairs pairs--justified"> <dt>Reputation </dt> <dd> <a href="/reputation/authors/klausst.544298" class="fauxBlockLink-linkRow u-concealed">9,887</a> </dd> </dl> <dl class="pairs pairs--justified"> <dt>Reaction score</dt> <dd>5,839</dd> </dl> <dl class="pairs pairs--justified pairs--xbBoxed trophyBlock"> <dt>Trophy points</dt> <dd>1,393</dd> </dl> <dl class="pairs pairs--justified creditBlock"> <dt title="Activity points">Activity points</dt> <dd> <a href="/activity/" data-xf-click="overlay" class="fauxBlockLink-blockLink u-concealed"> 178,866 </a> </dd> </dl> </div> <span class="message-userArrow"></span> </section> </div> <div class="message-cell message-cell--main"> <div class="message-main js-quickEditTarget"> <div class="message-content js-messageContent"> <div class="message-userContent lbContainer js-lbContainer " data-lb-id="post-1788892" data-lb-caption-desc="KlausST · Feb 18, 2025 at 10:42 AM"> <article class="message-body js-selectToQuote"> <div itemprop="text"> <div class="bbWrapper">Hi,<br /> <br /> why did you post in the "IC design" section? Do you want to design an IC on your own?<br /> <br /> <blockquote data-attributes="member: 694292" data-quote="abi0987654321" data-source="post: 1788887" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1788887" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1788887">abi0987654321 said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> How it is Vcst= 2.48mV? </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>the formula/explanation is given in "section 1"<br /> <br /> <blockquote data-attributes="member: 694292" data-quote="abi0987654321" data-source="post: 1788887" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1788887" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1788887">abi0987654321 said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> How did they derive Vcst=238mV? </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>Where do you find this?<br /> <br /> Klaus</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a href="/threads/led-driver-lm3409.414072/reply?quote=1788892" class="actionBar-action actionBar-action--reply" title="Reply, quoting this message" rel="nofollow" data-xf-click="quote" data-quote-href="/posts/1788892/quote">Reply</a> </div> </div> <div class="reactionsBar js-reactionsList "> </div> <br/> <div class="js-historyTarget message-historyTarget toggleTarget" data-href="trigger-href"></div> </footer> </div> </div> <div class="message-cell message-cell--vote"> <div class="message-column"> <div class="contentVote js-contentVote " data-xf-init="content-vote" data-content-id="post-1788892"> <meta itemprop="upvoteCount" content="0" /> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--up " data-vote="up"><span class="u-srOnly">Upvote</span></a> <span class="contentVote-score js-voteCount" data-score="0">0</span> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--down " data-vote="down"><span class="u-srOnly">Downvote</span></a> </div> </div> </div> </div> </article> <article class="message message--post js-post js-inlineModContainer " data-author="abi0987654321" data-content="post-1788894" id="js-post-1788894" itemscope itemtype="https://schema.org/Answer" itemid="https://www.edaboard.com/posts/1788894/"> <meta itemprop="parentItem" itemscope itemid="https://www.edaboard.com/threads/led-driver-lm3409.414072/" /> <span class="u-anchorTarget" id="post-1788894"></span> <div class="message-header"> <header class="message-attribution message-attribution--split"> <ul class="message-attribution-main listInline "> <li class="u-concealed"> <a href="/threads/led-driver-lm3409.414072/post-1788894" rel="nofollow" itemprop="url"> <time class="u-dt" dir="auto" datetime="2025-02-18T10:50:30+0000" data-time="1739875830" data-date-string="Feb 18, 2025" data-time-string="10:50 AM" title="Feb 18, 2025 at 10:50 AM" itemprop="datePublished">Today at 10:50 AM</time> </a> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <a href="/threads/led-driver-lm3409.414072/post-1788894" class="message-attribution-gadget" data-xf-init="share-tooltip" data-href="/posts/1788894/share" aria-label="Share" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </a> </li> <li> <a href="/threads/led-driver-lm3409.414072/post-1788894" rel="nofollow"> #3 </a> </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" itemprop="author" itemscope itemtype="https://schema.org/Person" itemid="https://www.edaboard.com/members/abi0987654321.694292/"> <meta itemprop="url" content="https://www.edaboard.com/members/abi0987654321.694292/" /> <div class="message-avatar "> <div class="message-avatar-wrapper"> <a href="/members/abi0987654321.694292/" class="avatar avatar--m avatar--default avatar--default--dynamic" data-user-id="694292" data-xf-init="member-tooltip" style="background-color: #521433; 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Do you want to design an IC on your own?<br /> <br /> the formula/explanation is given in "section 1"<br /> But op amp sees with ground ref. In that case Voltage will be 1.24 right. How op-amp sees 248mV. what principle they hav eused?<br /> <br /> Where do you find this? </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote><br /> Sorry it is 248mV. I have attached an image.<br /> <blockquote data-attributes="member: 544298" data-quote="KlausST" data-source="post: 1788892" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1788892" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1788892">KlausST said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> Klaus </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote></div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" 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694292" data-quote="abi0987654321" data-source="post: 1788887" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1788887" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1788887">abi0987654321 said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> I am having doubt on peak current control circuit (Rsns) section. Since op-Amp can ref voltage with ground. In that case voltage at non-inverting terminal should be 1.24v. How it is Vcst= 2.48mV? How Vcst=248mV will be the ref voltage to the comparartor? How did they derive Vcst=238mV? In what basic principle is used in that circuit analysis?<br /> <br /> <br /> Page N0=12<br /> <br /> This is the circuit </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>The calculation for Vcst is shown in your posted image of the circuit.....?</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a href="/threads/led-driver-lm3409.414072/reply?quote=1788896" class="actionBar-action actionBar-action--reply" title="Reply, quoting this message" rel="nofollow" data-xf-click="quote" data-quote-href="/posts/1788896/quote">Reply</a> </div> </div> <div class="reactionsBar js-reactionsList "> </div> <br/> <div class="js-historyTarget message-historyTarget toggleTarget" data-href="trigger-href"></div> </footer> </div> </div> <div class="message-cell message-cell--vote"> <div class="message-column"> <div class="contentVote js-contentVote " data-xf-init="content-vote" data-content-id="post-1788896"> <meta itemprop="upvoteCount" content="0" /> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--up " data-vote="up"><span class="u-srOnly">Upvote</span></a> <span class="contentVote-score js-voteCount" data-score="0">0</span> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--down " data-vote="down"><span class="u-srOnly">Downvote</span></a> </div> </div> </div> </div> </article> <article class="message message--post js-post js-inlineModContainer " data-author="abi0987654321" data-content="post-1788897" id="js-post-1788897" itemscope itemtype="https://schema.org/Answer" itemid="https://www.edaboard.com/posts/1788897/"> <meta itemprop="parentItem" itemscope itemid="https://www.edaboard.com/threads/led-driver-lm3409.414072/" /> <span class="u-anchorTarget" id="post-1788897"></span> <div class="message-header"> <header class="message-attribution message-attribution--split"> <ul class="message-attribution-main listInline "> <li class="u-concealed"> <a href="/threads/led-driver-lm3409.414072/post-1788897" rel="nofollow" itemprop="url"> <time class="u-dt" dir="auto" datetime="2025-02-18T13:09:54+0000" data-time="1739884194" data-date-string="Feb 18, 2025" data-time-string="1:09 PM" title="Feb 18, 2025 at 1:09 PM" itemprop="datePublished">Today at 1:09 PM</time> </a> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <a href="/threads/led-driver-lm3409.414072/post-1788897" class="message-attribution-gadget" data-xf-init="share-tooltip" data-href="/posts/1788897/share" aria-label="Share" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </a> </li> <li> <a href="/threads/led-driver-lm3409.414072/post-1788897" rel="nofollow"> #5 </a> </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" itemprop="author" itemscope itemtype="https://schema.org/Person" itemid="https://www.edaboard.com/members/abi0987654321.694292/"> <meta itemprop="url" content="https://www.edaboard.com/members/abi0987654321.694292/" /> <div class="message-avatar "> <div class="message-avatar-wrapper"> <a href="/members/abi0987654321.694292/" class="avatar avatar--m avatar--default avatar--default--dynamic" data-user-id="694292" data-xf-init="member-tooltip" style="background-color: #521433; 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What my doubt is, As per my understanding Vcst should be 1.24v with ref ground.so non inverting terminal reference should be 1.24v. But they calculated as Vcst=248mV which is reference for non inverting terminal. could you please explain how non inverting takes Vcst=248mV as reference? Or else proof or provide calculation that vcst=248mV will the reference not 1.24v</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a href="/threads/led-driver-lm3409.414072/reply?quote=1788897" class="actionBar-action actionBar-action--reply" title="Reply, quoting this message" rel="nofollow" data-xf-click="quote" data-quote-href="/posts/1788897/quote">Reply</a> </div> </div> <div class="reactionsBar js-reactionsList "> </div> <br/> <div class="js-historyTarget message-historyTarget toggleTarget" data-href="trigger-href"></div> </footer> </div> </div> <div class="message-cell message-cell--vote"> <div class="message-column"> <div class="contentVote js-contentVote " data-xf-init="content-vote" data-content-id="post-1788897"> <meta itemprop="upvoteCount" content="0" /> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--up " data-vote="up"><span class="u-srOnly">Upvote</span></a> <span class="contentVote-score js-voteCount" data-score="0">0</span> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--down " data-vote="down"><span class="u-srOnly">Downvote</span></a> </div> </div> </div> </div> </article> <article class="message message--post js-post js-inlineModContainer " data-author="std_match" data-content="post-1788898" id="js-post-1788898" itemscope itemtype="https://schema.org/Answer" itemid="https://www.edaboard.com/posts/1788898/"> <meta itemprop="parentItem" itemscope itemid="https://www.edaboard.com/threads/led-driver-lm3409.414072/" /> <span class="u-anchorTarget" id="post-1788898"></span> <div class="message-header"> <header class="message-attribution message-attribution--split"> <ul class="message-attribution-main listInline "> <li class="u-concealed"> <a href="/threads/led-driver-lm3409.414072/post-1788898" rel="nofollow" itemprop="url"> <time class="u-dt" dir="auto" datetime="2025-02-18T13:50:21+0000" data-time="1739886621" data-date-string="Feb 18, 2025" data-time-string="1:50 PM" title="Feb 18, 2025 at 1:50 PM" itemprop="datePublished">Today at 1:50 PM</time> </a> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <a href="/threads/led-driver-lm3409.414072/post-1788898" class="message-attribution-gadget" data-xf-init="share-tooltip" data-href="/posts/1788898/share" aria-label="Share" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </a> </li> <li> <a href="/threads/led-driver-lm3409.414072/post-1788898" rel="nofollow"> #6 </a> </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" itemprop="author" itemscope itemtype="https://schema.org/Person" itemid="https://www.edaboard.com/members/std_match.333403/"> <meta itemprop="url" content="https://www.edaboard.com/members/std_match.333403/" /> <div class="message-avatar "> <div class="message-avatar-wrapper"> <a href="/members/std_match.333403/" class="avatar avatar--m avatar--default avatar--default--dynamic" data-user-id="333403" data-xf-init="member-tooltip" style="background-color: #336699; 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It is the offset/reference for the upper comparator.<br /> 1.24V is the reference for the lower opamp. The current through the 5R resistor also goes through the R resistor next to the CSP pin.<br /> 1.24V over the 5R resistor will give 248 mV over the R resistor = Vcst.<br /> 248 mV = 1.24V / 5</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a href="/threads/led-driver-lm3409.414072/reply?quote=1788898" class="actionBar-action actionBar-action--reply" title="Reply, quoting this message" rel="nofollow" data-xf-click="quote" data-quote-href="/posts/1788898/quote">Reply</a> </div> </div> <div class="reactionsBar js-reactionsList "> </div> <br/> <div class="js-historyTarget 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<dd> <a href="/activity/" data-xf-click="overlay" class="fauxBlockLink-blockLink u-concealed"> 15,840 </a> </dd> </dl> </div> <span class="message-userArrow"></span> </section> </div> <div class="message-cell message-cell--main"> <div class="message-main js-quickEditTarget"> <div class="message-content js-messageContent"> <div class="message-userContent lbContainer js-lbContainer " data-lb-id="post-1788899" data-lb-caption-desc="danadakk · Feb 18, 2025 at 1:53 PM"> <article class="message-body js-selectToQuote"> <div itemprop="text"> <div class="bbWrapper">The OpAmp creates a current source at output of MOSFET it drives of<br /> 1.24V / 5R. That current flows thru R of the upper comparator creating<br /> a Vcst thru divider action of R/5R x 1.24</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a href="/threads/led-driver-lm3409.414072/reply?quote=1788899" class="actionBar-action actionBar-action--reply" title="Reply, quoting this message" rel="nofollow" data-xf-click="quote" data-quote-href="/posts/1788899/quote">Reply</a> </div> </div> <div class="reactionsBar js-reactionsList "> </div> <br/> <div class="js-historyTarget message-historyTarget toggleTarget" data-href="trigger-href"></div> </footer> </div> </div> <div class="message-cell message-cell--vote"> <div class="message-column"> <div class="contentVote js-contentVote " data-xf-init="content-vote" data-content-id="post-1788899"> <meta itemprop="upvoteCount" content="0" /> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--up " data-vote="up"><span class="u-srOnly">Upvote</span></a> <span class="contentVote-score js-voteCount" data-score="0">0</span> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--down " data-vote="down"><span class="u-srOnly">Downvote</span></a> </div> </div> </div> </div> </article> <article class="message message--post js-post js-inlineModContainer " data-author="abi0987654321" data-content="post-1788902" id="js-post-1788902" itemscope itemtype="https://schema.org/Answer" itemid="https://www.edaboard.com/posts/1788902/"> <meta itemprop="parentItem" itemscope itemid="https://www.edaboard.com/threads/led-driver-lm3409.414072/" /> <span class="u-anchorTarget" id="post-1788902"></span> <div class="message-header"> <header class="message-attribution message-attribution--split"> <ul class="message-attribution-main listInline "> <li class="u-concealed"> <a href="/threads/led-driver-lm3409.414072/post-1788902" rel="nofollow" itemprop="url"> <time class="u-dt" dir="auto" datetime="2025-02-18T14:48:50+0000" data-time="1739890130" data-date-string="Feb 18, 2025" data-time-string="2:48 PM" title="Feb 18, 2025 at 2:48 PM" itemprop="datePublished">Today at 2:48 PM</time> </a> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <a href="/threads/led-driver-lm3409.414072/post-1788902" class="message-attribution-gadget" data-xf-init="share-tooltip" data-href="/posts/1788902/share" aria-label="Share" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </a> </li> <li> <a href="/threads/led-driver-lm3409.414072/post-1788902" rel="nofollow"> #8 </a> </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" itemprop="author" itemscope itemtype="https://schema.org/Person" itemid="https://www.edaboard.com/members/abi0987654321.694292/"> <meta itemprop="url" content="https://www.edaboard.com/members/abi0987654321.694292/" /> <div class="message-avatar "> <div class="message-avatar-wrapper"> <a href="/members/abi0987654321.694292/" class="avatar avatar--m avatar--default avatar--default--dynamic" data-user-id="694292" data-xf-init="member-tooltip" style="background-color: #521433; 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That current flows thru R of the upper comparator creating<br /> a Vcst thru divider action of R/5R x 1.24 </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>Could you please explain how the current path. Since vcsp is the high potential how current flows from 5R to Vcst ,R ?</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a href="/threads/led-driver-lm3409.414072/reply?quote=1788902" class="actionBar-action actionBar-action--reply" title="Reply, quoting this message" rel="nofollow" data-xf-click="quote" data-quote-href="/posts/1788902/quote">Reply</a> </div> </div> <div class="reactionsBar js-reactionsList "> </div> <br/> <div class="js-historyTarget message-historyTarget toggleTarget" data-href="trigger-href"></div> </footer> </div> </div> <div class="message-cell message-cell--vote"> <div class="message-column"> <div class="contentVote js-contentVote " data-xf-init="content-vote" data-content-id="post-1788902"> <meta itemprop="upvoteCount" content="0" /> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--up " data-vote="up"><span class="u-srOnly">Upvote</span></a> <span class="contentVote-score js-voteCount" data-score="0">0</span> <a href="javascript:" class="contentVote-vote is-disabled contentVote-vote--down " data-vote="down"><span class="u-srOnly">Downvote</span></a> </div> </div> </div> </div> </article> <article class="message message--post js-post js-inlineModContainer " data-author="abi0987654321" data-content="post-1788903" id="js-post-1788903" itemscope itemtype="https://schema.org/Answer" itemid="https://www.edaboard.com/posts/1788903/"> <meta itemprop="parentItem" itemscope itemid="https://www.edaboard.com/threads/led-driver-lm3409.414072/" /> <span class="u-anchorTarget" id="post-1788903"></span> <div class="message-header"> <header class="message-attribution message-attribution--split"> <ul class="message-attribution-main listInline "> <li class="u-concealed"> <a href="/threads/led-driver-lm3409.414072/post-1788903" rel="nofollow" itemprop="url"> <time class="u-dt" dir="auto" datetime="2025-02-18T14:50:17+0000" data-time="1739890217" data-date-string="Feb 18, 2025" data-time-string="2:50 PM" title="Feb 18, 2025 at 2:50 PM" itemprop="datePublished">Today at 2:50 PM</time> </a> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <a href="/threads/led-driver-lm3409.414072/post-1788903" class="message-attribution-gadget" data-xf-init="share-tooltip" data-href="/posts/1788903/share" aria-label="Share" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </a> </li> <li> <a href="/threads/led-driver-lm3409.414072/post-1788903" rel="nofollow"> #9 </a> </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" itemprop="author" itemscope itemtype="https://schema.org/Person" itemid="https://www.edaboard.com/members/abi0987654321.694292/"> <meta itemprop="url" content="https://www.edaboard.com/members/abi0987654321.694292/" /> <div class="message-avatar "> <div class="message-avatar-wrapper"> <a href="/members/abi0987654321.694292/" class="avatar avatar--m avatar--default avatar--default--dynamic" data-user-id="694292" data-xf-init="member-tooltip" style="background-color: #521433; 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It is the offset/reference for the upper comparator.<br /> 1.24V is the reference for the lower opamp. The current through the 5R resistor also goes through the R resistor next to the CSP pin.<br /> 1.24V over the 5R resistor will give 248 mV over the R resistor = Vcst.<br /> 248 mV = 1.24V / 5 </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>How current flows form low to high potential.since Vcsp is at high potential.current flows from vcsp to R to 5R.rit</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a href="/threads/led-driver-lm3409.414072/reply?quote=1788903" class="actionBar-action 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<article class="message-body js-selectToQuote"> <div itemprop="text"> <div class="bbWrapper">dear abi <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite2" alt=";)" title="Wink ;)" loading="lazy" data-shortname=";)" /><br /> <br /> If I<span style="font-size: 9px">T</span> = max, then 1.24V = 5*Vcst due to single current path and FET V drop. depends on Vin - 6/5*1.24<br /> Since CSN pin has no current, <b>V</b><span style="font-size: 9px"><b>SNS</b></span><b>=V</b><span style="font-size: 9px"><b>CST </b>= </span><span style="font-size: 15px">1.24/5</span><br /> <br /> <div class="bbImageWrapper js-lbImage" title="1739894493368.png" data-src="https://www.edaboard.com/attachments/1739894493368-png.197414/" data-lb-sidebar-href="" data-lb-caption-extra-html="" data-single-image="1"> <img src="https://www.edaboard.com/attachments/1739894493368-png.197414/" data-url="" class="bbImage" data-zoom-target="1" 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</section> </div> <div class="message-cell message-cell--main"> <div class="message-main js-quickEditTarget"> <div class="message-content js-messageContent"> <div class="message-userContent lbContainer js-lbContainer " data-lb-id="post-1788911" data-lb-caption-desc="abi0987654321 · Feb 18, 2025 at 3:57 PM"> <article class="message-body js-selectToQuote"> <div itemprop="text"> <div class="bbWrapper"><blockquote data-attributes="member: 134022" data-quote="D.A.(Tony)Stewart" data-source="post: 1788910" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1788910" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1788910">D.A.(Tony)Stewart said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> dear abi <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite2" alt=";)" title="Wink ;)" loading="lazy" data-shortname=";)" /><br /> <br /> If I<span style="font-size: 9px">T</span> = max, then 1.24V = 5*Vcst due to single current path and FET is 0V drop. at threshold.<br /> Since CSN pin has no current, <b>V</b><span style="font-size: 9px"><b>SNS</b></span><b>=V</b><span style="font-size: 9px"><b>CST </b>= </span><span style="font-size: 15px">1.24/5</span><br /> <br /> <a href="https://www.edaboard.com/attachments/197413/" target="_blank">View attachment 197413</a> </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>Sorry, Im not understanding your explanation.could you please elaborate?</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta 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18, 2025 at 6:36 PM"> <article class="message-body js-selectToQuote"> <div itemprop="text"> <div class="bbWrapper"><blockquote data-attributes="member: 694292" data-quote="abi0987654321" data-source="post: 1788911" class="bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch"> <div class="bbCodeBlock-title"> <a href="/goto/post?id=1788911" class="bbCodeBlock-sourceJump" rel="nofollow" data-xf-click="attribution" data-content-selector="#post-1788911">abi0987654321 said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> Sorry, Im not understanding your explanation.could you please elaborate? </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>What exactly don´t you understand. <br /> All parts are marked, you see the 1.24V refeerence, the 5R, the R, .. also Tony showed you the current path ... so I can´t imagine what is unclear. <br /> <br /> Klaus</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a href="/threads/led-driver-lm3409.414072/reply?quote=1788917" class="actionBar-action actionBar-action--reply" title="Reply, quoting this message" rel="nofollow" data-xf-click="quote" data-quote-href="/posts/1788917/quote">Reply</a> </div> </div> <div class="reactionsBar js-reactionsList "> </div> <br/> <div class="js-historyTarget message-historyTarget toggleTarget" data-href="trigger-href"></div> </footer> </div> </div> <div class="message-cell message-cell--vote"> <div class="message-column"> <div 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data-content-selector="#post-1788911">abi0987654321 said:</a> </div> <div class="bbCodeBlock-content"> <div class="bbCodeBlock-expandContent js-expandContent "> Sorry, Im not understanding your explanation.could you please elaborate? </div> <div class="bbCodeBlock-expandLink js-expandLink"><a role="button" tabindex="0">Click to expand...</a></div> </div> </blockquote>Can you elaborate what you do understand? <br /> Virtual null in Op Amp inputs, controlled by Vin+<br /> Voltage controlled current?</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a 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Reload the page for the latest version.", server_did_not_respond_in_time_try_again: "The server did not respond in time. Please try again.", oops_we_ran_into_some_problems: "Oops! We ran into some problems.", oops_we_ran_into_some_problems_more_details_console: "Oops! We ran into some problems. Please try again later. More error details may be in the browser console.", file_too_large_to_upload: "The file is too large to be uploaded.", uploaded_file_is_too_large_for_server_to_process: "The uploaded file is too large for the server to process.", files_being_uploaded_are_you_sure: "Files are still being uploaded. Are you sure you want to submit this form?", attach: "Attach files", rich_text_box: "Rich text box", close: "Close", link_copied_to_clipboard: "Link copied to clipboard.", text_copied_to_clipboard: "Text copied to clipboard.", loading: "Loading…", you_have_exceeded_maximum_number_of_selectable_items: "You have exceeded the maximum number of selectable items.", processing: "Processing", 'processing...': "Processing…", showing_x_of_y_items: "Showing {count} of {total} items", showing_all_items: "Showing all items", no_items_to_display: "No items to display", number_button_up: "Increase", number_button_down: "Decrease", push_enable_notification_title: "Push notifications enabled successfully at Forum for Electronics", push_enable_notification_body: "Thank you for enabling push notifications!", pull_down_to_refresh: "Pull down to refresh", release_to_refresh: "Release to refresh", refreshing: "Refreshing…" , "svStandardLib_time.day": "{count} day", "svStandardLib_time.days": "{count} days", "svStandardLib_time.hour": "{count} hour", "svStandardLib_time.hours": "{count} hours", "svStandardLib_time.minute": "{count} minutes", "svStandardLib_time.minutes": "{count} minutes", "svStandardLib_time.month": "{count} month", "svStandardLib_time.months": "{count} months", "svStandardLib_time.second": "{count} second", "svStandardLib_time.seconds": "{count} seconds", "svStandardLib_time.week": "time.week", "svStandardLib_time.weeks": "{count} weeks", "svStandardLib_time.year": "{count} year", "svStandardLib_time.years": "{count} years" }); </script> <form style="display:none" hidden="hidden"> <input type="text" name="_xfClientLoadTime" value="" id="_xfClientLoadTime" title="_xfClientLoadTime" tabindex="-1" /> </form>  <script type="application/ld+json"> { "@context": "https://schema.org", "@type": "QAPage", "url": "https://www.edaboard.com/threads/led-driver-lm3409.414072/", "mainEntity": { "@type": "Question", "@id": "https://www.edaboard.com/threads/led-driver-lm3409.414072/", "name": "LED Driver LM3409", "datePublished": "2025-02-18T08:48:07+00:00", "dateModified": "2025-02-18T10:00:49+00:00", "url": "https://www.edaboard.com/threads/led-driver-lm3409.414072/", "image": "https://www.edaboard.com/attachments/screenshot-2025-02-17-123352-png.197411/", "text": "I am having doubt on peak current control circuit (Rsns) section. Since op-Amp can ref voltage with ground. In that case voltage at non-inverting terminal should be 1.24v. How it is Vcst= 2.48mV? How Vcst=248mV will be the ref voltage to the comparartor? How did they derive Vcst=238mV? In what basic principle is used in that circuit analysis?\n\n\nPage N0=12\n\nThis is the circuit", "answerCount": 12, "upvoteCount": 0, "author": { "@type": "Person", "@id": "https://www.edaboard.com/members/abi0987654321.694292/", "name": "abi0987654321", "url": "https://www.edaboard.com/members/abi0987654321.694292/" }, "suggestedAnswer": [ { "@type": "Answer", "datePublished": "2025-02-18T21:11:29+00:00", "url": "https://www.edaboard.com/posts/1788919/", "text": "Sorry, Im not understanding your explanation.could you please elaborate?\n\nCan you elaborate what you do understand? \nVirtual null in Op Amp inputs, controlled by Vin+\nVoltage controlled current?", "upvoteCount": 0, "author": { "@type": "Person", "@id": "https://www.edaboard.com/members/d-a-tony-stewart.134022/", "name": "D.A.(Tony)Stewart", "url": "https://www.edaboard.com/members/d-a-tony-stewart.134022/" } }, { "@type": "Answer", "datePublished": "2025-02-18T18:36:15+00:00", "url": "https://www.edaboard.com/posts/1788917/", "text": "Sorry, Im not understanding your explanation.could you please elaborate?\n\nWhat exactly don\u00b4t you understand. \nAll parts are marked, you see the 1.24V refeerence, the 5R, the R, .. also Tony showed you the current path ... so I can\u00b4t imagine what is unclear. \n\nKlaus", "upvoteCount": 0, "author": { "@type": "Person", "@id": "https://www.edaboard.com/members/klausst.544298/", "name": "KlausST", "url": "https://www.edaboard.com/members/klausst.544298/" } }, { "@type": "Answer", "datePublished": "2025-02-18T15:57:07+00:00", "url": "https://www.edaboard.com/posts/1788911/", "text": "dear abi ;)\n\nIf IT = max, then 1.24V = 5*Vcst due to single current path and FET is 0V drop. at threshold.\nSince CSN pin has no current, VSNS=VCST = 1.24/5\n\n\n\nSorry, Im not understanding your explanation.could you please elaborate?", "upvoteCount": 0, "author": { "@type": "Person", "@id": "https://www.edaboard.com/members/abi0987654321.694292/", "name": "abi0987654321", "url": "https://www.edaboard.com/members/abi0987654321.694292/" } } ] }, "publisher": { "@type": "Organization", "name": "Forum for Electronics", "description": "International Electronics Discussion Forum: EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals", "url": "https://www.edaboard.com" } } </script> <script> $(function(){ var notice = $('.xb-welcome-notice'); if(notice.length){ var cookie = XF.Cookie.get('hide_welcome_notice'); if(!cookie){ XF.Cookie.set('hide_welcome_notice', Date.now()); notice.show(); } else if ((Date.now() - cookie) > 8.64e+7){ XF.Cookie.set('hide_welcome_notice', Date.now()); notice.show(); } else { notice.hide(); } } }); </script> </div> </body> </html>

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