{"id":9290,"date":"2020-06-14T19:13:58","date_gmt":"2020-06-14T19:13:58","guid":{"rendered":"https:\/\/stevepedwards.today\/stevepedwards.com\/ElectronicsStuff\/?p=9290"},"modified":"2020-08-04T10:41:34","modified_gmt":"2020-08-04T09:41:34","slug":"astable-multivibrator-duty-cycle-from-0-to-100","status":"publish","type":"post","link":"https:\/\/stevepedwards.today\/ElectronicsStuff\/astable-multivibrator-duty-cycle-from-0-to-100\/","title":{"rendered":"555 Astable Multivibrator – Duty Cycle From 0 To 100%"},"content":{"rendered":"

From AdvancedElectronicsManual.pdf
\nAdvanced Electronics Manual.pdf<\/a>
\nAstable multivibrator with duty cycle variable from 0 to 100%:<\/em>
\nIn some applications, it is needed to vary the duty cycle from about 0 to 100%. In that case the circuit is designed as shown in the circuit diagram. Here a potentiometer, RX, is used so that RA = R1+R2, RB = RX-R2+R3. A diode is now connected across a variable RB.<\/em>
\nThus a variable duty cycle is achieved. Therefore, the frequency of oscillation and duty cycle can be derived as follows.<\/em>
\nThe time for charging C from 1\/3 to 2\/3 Vcc, i.e, ON Time = 0.693 (RA + RB). C The time for discharging C from 2\/3 to 1\/3 Vcc, i.e. OFF Time = 0.693 RB. C To get the total oscillation period, just add the two:
\nTosc = 0.693\u00e2\u02c6\u2122(RA+RB)\u00e2\u02c6\u2122C + 0.693\u00e2\u02c6\u2122(RB)\u00e2\u02c6\u2122C = 0.693 \u00e2\u02c6\u2122 (RA + 2\u00e2\u02c6\u2122RB) \u00e2\u02c6\u2122 C<\/strong>
\nfosc = 1\/ Tosc = 1.44\/(RA + RB).C = 1.44\/(R1 + RX + R3).C<\/strong>
\nMin. Duty Cycle = R1\/(R1 + RX + R3)<\/strong>
\nMax. Duty Cycle = (R1 + RX)\/(R1 + RX + R3)<\/strong>
\n\"\"
\nI had only a 5k trim pot and 1.5k\/2k5 resistors, not 10k\/1k so could only get about 20% to 66% duty cycles not 0-100% as this circuit claims:
\n\"\"
\n\"\"
\nDong the calcs for my values:
\nMin. Duty Cycle = R1\/(R1 + RX + R3)<\/strong>
\nMin. Duty Cycle<\/strong> = R1\/(R1 + RX + R3) = 1500 \/ (1500+5000+2500 = 9000 ) =
\n15\/90 = 1\/6 = 17%<\/strong>
\nMax. Duty Cycle<\/strong> = (R1 + RX)\/(R1 + RX + R3) = 1500 + 5000 \/ (1500+5000+2500 = 9000 ) = 6500 \/ 9000 = 0.72 = 72%<\/strong>
\nI added another 5k trim and got these results at max and minimum resistance:
\n\"\" \"\"
\nThis has changed both duty cycles from about 1\/6 to 3\/4:
\nMin. Duty Cycle = R1\/(R1 + RX + R3)<\/strong>
\nMin. Duty Cycle<\/strong> = R1\/(R1 + RX + R3) = 1500 \/ (1500+10000+2500 = 14000 ) =
\n1500\/14000 = 15\/140 = 10.7%<\/strong>
\nMax. Duty Cycle<\/strong> = (R1 + RX)\/(R1 + RX + R3) = 1500 + 10000 \/ (1500+10000+2500 = 14000 ) = 11500 \/ 14000= 82%<\/strong>
\nThe capacitor charge was read from pins 6\/2.<\/p>\n","protected":false},"excerpt":{"rendered":"

From AdvancedElectronicsManual.pdf Advanced Electronics Manual.pdf Astable multivibrator with duty cycle variable from 0 to 100%: In some applications, it is needed to vary the duty cycle from about 0 to 100%. In that case the circuit is designed as shown in the circuit diagram. Here a potentiometer, RX, is used so that RA = R1+R2, ... 555 Astable Multivibrator – Duty Cycle From 0 To 100%<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[],"class_list":["post-9290","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/stevepedwards.today\/ElectronicsStuff\/wp-json\/wp\/v2\/posts\/9290","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/stevepedwards.today\/ElectronicsStuff\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/stevepedwards.today\/ElectronicsStuff\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/stevepedwards.today\/ElectronicsStuff\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/stevepedwards.today\/ElectronicsStuff\/wp-json\/wp\/v2\/comments?post=9290"}],"version-history":[{"count":1,"href":"https:\/\/stevepedwards.today\/ElectronicsStuff\/wp-json\/wp\/v2\/posts\/9290\/revisions"}],"predecessor-version":[{"id":9332,"href":"https:\/\/stevepedwards.today\/ElectronicsStuff\/wp-json\/wp\/v2\/posts\/9290\/revisions\/9332"}],"wp:attachment":[{"href":"https:\/\/stevepedwards.today\/ElectronicsStuff\/wp-json\/wp\/v2\/media?parent=9290"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/stevepedwards.today\/ElectronicsStuff\/wp-json\/wp\/v2\/categories?post=9290"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/stevepedwards.today\/ElectronicsStuff\/wp-json\/wp\/v2\/tags?post=9290"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}