{"id":491,"date":"2025-06-08T15:48:43","date_gmt":"2025-06-08T15:48:43","guid":{"rendered":"https:\/\/daq-design.co.uk\/blog\/?p=491"},"modified":"2025-06-10T16:51:48","modified_gmt":"2025-06-10T16:51:48","slug":"simple-voltage-regulator","status":"publish","type":"post","link":"https:\/\/daq-design.co.uk\/blog\/?p=491","title":{"rendered":"Simple Voltage Regulator"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">A Simple 5 Volt regulator using an NPN Transistor and a Zener Diode. Circuit drawn in <a href=\"https:\/\/daq-design.co.uk\/sim\/circuitjs.html?startCircuit=gw001.txt\" target=\"_blank\" rel=\"noreferrer noopener\">Falstad Circuit Simulator<\/a><\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"878\" height=\"524\" src=\"https:\/\/daq-design.co.uk\/blog\/wp-content\/uploads\/2025\/06\/Screenshot-HP-2025-06-08-at-16.52.39.jpg\" alt=\"\" class=\"wp-image-500\" srcset=\"https:\/\/daq-design.co.uk\/blog\/wp-content\/uploads\/2025\/06\/Screenshot-HP-2025-06-08-at-16.52.39.jpg 878w, https:\/\/daq-design.co.uk\/blog\/wp-content\/uploads\/2025\/06\/Screenshot-HP-2025-06-08-at-16.52.39-300x179.jpg 300w, https:\/\/daq-design.co.uk\/blog\/wp-content\/uploads\/2025\/06\/Screenshot-HP-2025-06-08-at-16.52.39-768x458.jpg 768w, https:\/\/daq-design.co.uk\/blog\/wp-content\/uploads\/2025\/06\/Screenshot-HP-2025-06-08-at-16.52.39-800x477.jpg 800w\" sizes=\"auto, (max-width: 878px) 100vw, 878px\" \/><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">It doesn&#8217;t get much simpler that this, well, it does actually if you don&#8217;t use a transistor but you won&#8217;t get much current delivery.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The key to the circuit is in knowing a number of variables:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>What do you want the load current to be?<\/li>\n\n\n\n<li>What do you want the output voltage to be?<\/li>\n\n\n\n<li>What is the likely input voltage going to be?<\/li>\n\n\n\n<li>What&#8217;s the gain (hfe) of the NPN transistor?<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>How it works.<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A Zener diode is used as a voltage reference, in this circuit the voltage is 5.6V. This voltage is supplied to the base of the transistor and the forward volt drop of the base-emitter junction reduces the output at the emitter to (Vz-Vbe) 5.6-0.6=5V.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The input voltage can vary and using Kirchoff&#8217;s law there will be a voltage drop across the sense resistor of Vin-Vz and and a current flow. The resistor also provides the bias current for the transistor to ensure it turns on. So, there are two currents to consider in the base circuit.<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Iz. The Zener needs somewhere between 5 and 10mA to maintain the 5.6V reference voltage at the base.<\/li>\n\n\n\n<li>Ib. This is related to the gain of the transistor and the output current. The base current can be calculated as Ic\/hfe. We know hfe and we know the design current from the requirements.<\/li>\n\n\n\n<li>ib&lt;&lt; iz.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Calculating Rs.<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The sense resistor can now be calculated using a simple Ohm&#8217;s law calculation:<\/p>\n\n\n\n<figure class=\"wp-block-image size-full is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"460\" height=\"144\" src=\"https:\/\/daq-design.co.uk\/blog\/wp-content\/uploads\/2025\/06\/Rs_Basic.png\" alt=\"\" class=\"wp-image-557\" style=\"width:198px;height:auto\" srcset=\"https:\/\/daq-design.co.uk\/blog\/wp-content\/uploads\/2025\/06\/Rs_Basic.png 460w, https:\/\/daq-design.co.uk\/blog\/wp-content\/uploads\/2025\/06\/Rs_Basic-300x94.png 300w\" sizes=\"auto, (max-width: 460px) 100vw, 460px\" \/><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">For our simple use case, these are the core requirements.<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>ILoad=30mA<\/li>\n\n\n\n<li>Vs=9V<\/li>\n\n\n\n<li>Vout=5V<\/li>\n\n\n\n<li>hfe=100<\/li>\n\n\n\n<li>Iz=5mA<\/li>\n<\/ul>\n\n\n\n<figure class=\"wp-block-image size-full is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1403\" height=\"120\" src=\"https:\/\/daq-design.co.uk\/blog\/wp-content\/uploads\/2025\/06\/RS_640.png\" alt=\"\" class=\"wp-image-539\" style=\"width:550px;height:auto\" srcset=\"https:\/\/daq-design.co.uk\/blog\/wp-content\/uploads\/2025\/06\/RS_640.png 1403w, https:\/\/daq-design.co.uk\/blog\/wp-content\/uploads\/2025\/06\/RS_640-300x26.png 300w, https:\/\/daq-design.co.uk\/blog\/wp-content\/uploads\/2025\/06\/RS_640-1024x88.png 1024w, https:\/\/daq-design.co.uk\/blog\/wp-content\/uploads\/2025\/06\/RS_640-768x66.png 768w, https:\/\/daq-design.co.uk\/blog\/wp-content\/uploads\/2025\/06\/RS_640-800x68.png 800w\" sizes=\"auto, (max-width: 1403px) 100vw, 1403px\" \/><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">As this isn&#8217;t a preferred value, chose a lower value to ensure sufficient bias is applied to the transistor : 620\u03a9<\/p>\n","protected":false},"excerpt":{"rendered":"<p>A Simple 5 Volt regulator using an NPN Transistor and a Zener Diode. Circuit drawn in Falstad Circuit Simulator It doesn&#8217;t get much simpler that this, well, it does actually if you don&#8217;t use a transistor but you won&#8217;t get &hellip; <a href=\"https:\/\/daq-design.co.uk\/blog\/?p=491\">Continue reading <span class=\"meta-nav\">&rarr;<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6],"tags":[34,26,33],"class_list":["post-491","post","type-post","status-publish","format-standard","hentry","category-transistors","tag-falstad","tag-transistor","tag-zener-diode"],"_links":{"self":[{"href":"https:\/\/daq-design.co.uk\/blog\/index.php?rest_route=\/wp\/v2\/posts\/491","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/daq-design.co.uk\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/daq-design.co.uk\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/daq-design.co.uk\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/daq-design.co.uk\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=491"}],"version-history":[{"count":18,"href":"https:\/\/daq-design.co.uk\/blog\/index.php?rest_route=\/wp\/v2\/posts\/491\/revisions"}],"predecessor-version":[{"id":517,"href":"https:\/\/daq-design.co.uk\/blog\/index.php?rest_route=\/wp\/v2\/posts\/491\/revisions\/517"}],"wp:attachment":[{"href":"https:\/\/daq-design.co.uk\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=491"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/daq-design.co.uk\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=491"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/daq-design.co.uk\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=491"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}