[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"doc-seo-562769-105":3,"detail-sidebar-cat-0-en-105":81,"doc-detail-562769-en":130},{"code":4,"msg":5,"data":6},0,"ok",{"site_id":7,"language":8,"slug":9,"title":10,"keywords":11,"description":12,"schema_data":13,"social_meta":74,"head_meta":76,"extra_data":78,"updated_unix":80},105,"en","power-supply-relay-based-ac-to-dc-voltage-doubler","Power supply - relay based AC-to-DC voltage doubler","","Explains how a relay stage and an AC-to-DC power supply are implemented and how their protective and timing behavior works. Describes voltage division, hysteresis, and capacitor discharge required before the relay turns off, plus diode protection against relay turn-off spikes. Details the ±12V rails generated from mains using a 330nF X2 capacitor, current-limiting resistor, dual half-wave rectifiers, Zener limiting to about 11.5V, and discharge/inrush control; estimates currents and resulting rail drop when the relay is energized.",{"@graph":14,"@context":73},[15,34,56],{"@type":16,"itemListElement":17},"BreadcrumbList",[18,23,27,31],{"item":19,"name":20,"@type":21,"position":22},"https://docshare.wps.com","Home","ListItem",1,{"item":24,"name":25,"@type":21,"position":26},"https://docshare.wps.com/document/","Document",2,{"item":28,"name":29,"@type":21,"position":30},"https://docshare.wps.com/document/technology/","Technology",3,{"item":32,"name":10,"@type":21,"position":33},"https://docshare.wps.com/document/power-supply-relay-based-ac-to-dc-voltage-doubler/562769/",4,{"url":32,"name":10,"@type":35,"image":36,"author":41,"headline":10,"publisher":44,"fileFormat":47,"inLanguage":8,"description":12,"dateModified":48,"datePublished":49,"encodingFormat":47,"isAccessibleForFree":50,"interactionStatistic":51},"DigitalDocument",{"url":37,"@type":38,"width":39,"height":40},"https://docshare.wps.com/thumbnails/power-supply-relay-based-ac-to-dc-voltage-doubler/562769.png","ImageObject",300,407,{"name":42,"@type":43},"hdkawk","Person",{"url":19,"name":45,"@type":46},"DocShare","Organization","application/pdf","2026-10-22","2026-10-12",true,{"@type":52,"interactionType":53,"userInteractionCount":55},"InteractionCounter",{"@type":54},"ViewAction",7,{"@type":57,"mainEntity":58},"FAQPage",[59,65,69],{"name":60,"@type":61,"acceptedAnswer":62},"Why is capacitor discharge required before the relay turns off?","Question",{"text":63,"@type":64},"The hysteresis for the stage means the capacitor must discharge by an additional amount before the relay input reaches the turn-off threshold.","Answer",{"name":66,"@type":61,"acceptedAnswer":67},"How are the ±12V rails generated from the mains supply?",{"text":68,"@type":64},"A 330nF X2 capacitor and 470Ω current-limiting resistor feed a dual half-wave rectifier using diodes D1 and D2, charging 220µF capacitors alternately to form positive and negative rails.",{"name":70,"@type":61,"acceptedAnswer":71},"What limits the voltage and current in the supply?",{"text":72,"@type":64},"12V Zener diodes (ZD1 and ZD2) limit capacitor voltage to about 11.5V, while the X2 capacitor impedance at 50Hz limits mains current to roughly 24mA; the 470Ω resistor further reduces dissipation and shapes current 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stage,and thecapacitor must discharge by this addi-tionalamount before the relay turns off.  \nThis allows the relay to stay onthrough brief dips in the load current.Diode D5 protects transistor Q1 fromany voltage spike created when therelay turns off.  \n# Power supply\n\nThe ±12V rails are derived from themainslive line viaa 330nFX2 series ca-pacitor,470Ω current-limiting resistorand dual half-wave rectifier formed bydiodes D1and D2.These diodes chargethe 220μF capacitors alternately witheach mains half-cycle,to provide thepositive and negative rails.12V Zenerdiodes ZD1 and ZD2 limit the voltageacross these capacitors to about 11.5V.The 330nF capacitor and470Q resistorlimit the current and thus dissipationin ZD1 and ZD2 to well below theirrated 1W.  \nIf you ignore the X2 capacitor andtwo 1W resistors,this is a traditionalAC-to-DC voltage doubler supply.TheX2 capacitor has an impedance at 50Hzof around 9.65kΩ,which limits themains current to about 230V÷9.65kΩ=24mA.It's a bit more complicatedthan this calculation implies,but that'sa reasonable approximation.  \nWe could have used a wirewoundresistor of a similar value,but it wouldthen dissipate 0.024A²×9.65kΩ =  \n5.5W.The capacitor dissipates virtu-ally no power.  \nThe parallel 10MΩ resistor dis-charges theX2 capacitor once power isremoved,while the 470Ωseries resistorlimits the inrush current when poweris first applied.  \nFor more details on how this type ofsupply works,see the description in theoriginal Soft Starterarticle(April2013).  \nThe specified relay has a nominalcoil resistance of 1.1kΩ.This meanswith a 24V supply it will draw around22mA.As stated earlier,the X2 capaci-tor limits the supply current to about24mA;less due to the series 470Ωresistor and other factors.  \nWhen the relay is turned on,the X2capacitor and 470Ω resistor form avolt-age divider with the coil resistance.Thesupply rails then dropto about±6Vandthe two Zener diodes cease conducting,since most of the input current flowsthrough the relay coil.","cbCaiviTDnfddGSp","https://ap.wps.com/l/cbCaiviTDnfddGSp","pdf",708759,"English","# Power supply\n## Relay stage hysteresis and turn-off behavior\n## Deriving ±12V rails from mains\n## Voltage limiting, current limiting, and dissipation\n## Discharge and inrush control\n## Relay coil current and voltage droop","[{\"question\":\"Why is capacitor discharge required before the relay turns off?\",\"answer\":\"The hysteresis for the stage means the capacitor must discharge by an additional amount before the relay input reaches the turn-off threshold.\"},{\"question\":\"How are the ±12V rails generated from the mains supply?\",\"answer\":\"A 330nF X2 capacitor and 470Ω current-limiting resistor feed a dual half-wave rectifier using diodes D1 and D2, charging 220µF capacitors alternately to form positive and negative rails.\"},{\"question\":\"What limits the voltage and current in the supply?\",\"answer\":\"12V Zener diodes (ZD1 and ZD2) limit capacitor voltage to about 11.5V, while the X2 capacitor impedance at 50Hz limits mains current to roughly 24mA; the 470Ω resistor further reduces dissipation and shapes current flow.\"}]","Power supply - relay based AC-to-DC voltage doubler | PDF",1791809696]