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Electronics Forum / Electronics / May 2007powering a 555 off mains
I'd like to make a 555 PWM speed controller to drive a mosfet and switch a 240V DC motor that normally runs off a TRIAC circuit fed into a bridge rectifier. The TRIAC controller normally is set up to output 240V max from the 340V rectified mains and while it works ok has no low down torque and outputs an awful lot of RF interference. My main query is this: what's a simple effective way to generate the 12V DC or so to power a 555 IC off 340V DC?. I was mainly considering a power resistor/zener combination. > I'd like to make a 555 PWM speed controller to drive >a mosfet and switch a 240V DC motor that normally runs off [quoted text clipped - 6 lines] >generate the 12V DC or so to power a 555 IC off 340V DC?. >I was mainly considering a power resistor/zener combination. That's how it's done in cheap household appliances, eg timers, toasters. See http://www.users.on.net/~fzabkar/Toaster_5698123.pdf - Franc Zabkar  SignaturePlease remove one 'i' from my address when replying by email. >> I'd like to make a 555 PWM speed controller to drive >>a mosfet and switch a 240V DC motor that normally runs off [quoted text clipped - 13 lines] > > - Franc Zabkar Hey Franc Did ya get that lighting cct sorted ?? SignatureCheers .......... Rheilly P >Hey Franc >Did ya get that lighting cct sorted ?? If you're referring to that recent continuation of a very old thread (22 Feb 2007), then the OP with the problem was Nick Hobbs, not me. http://groups.google.com/group/aus.electronics/msg/0f2f422b77dac3a7?dmode=source &hl=en - Franc Zabkar SignaturePlease remove one 'i' from my address when replying by email. "Mark Harriss" > I'd like to make a 555 PWM speed controller to drive > a mosfet and switch a 240V DC motor that normally runs off > a TRIAC circuit fed into a bridge rectifier. ** Totally nuts idea. > The TRIAC > controller normally is set up to output 240V max from the > 340V rectified mains and while it works ok has no low down > torque and outputs an awful lot of RF interference. ** ROTFL So what fool's magic will make using a MOSFET any different ?? Go have a look at a *half wave* SCR drill speed control - low speed torque is kept high by the use of back emf induced feedback of the firing phase. Many kits designs have been published by EA and SC. ...... Phil I wondered if my post would bring you flapping out of the woodwork of Nostradamus' coffin. > I'd like to make a 555 PWM speed controller to drive >a mosfet and switch a 240V DC motor that normally runs off >a TRIAC circuit fed into a bridge rectifier. The TRIAC >controller normally is set up to output 240V max from the >340V rectified mains ... Is this a treadmill application? Just curious ... - Franc Zabkar SignaturePlease remove one 'i' from my address when replying by email. > Is this a treadmill application? Just curious ... > > - Franc Zabkar Production gemstone faceting machines Frank, the speed controller sits in an earthed, cast metal box and they've been made for 40 odd years using triacs but the lack of low end speed and the bad interference as well as some false triggering problems when you have more than one unit on the same powerpoint makes me want to evaluate a slightly more recent design principle. >> Is this a treadmill application? Just curious ... >> [quoted text clipped - 6 lines] >have more than one unit on the same powerpoint makes me want to >evaluate a slightly more recent design principle. FWIW, I see used MOSFET based (?) PWM treadmill DC motor controllers (120V) on Ebay for US$60. - Franc Zabkar SignaturePlease remove one 'i' from my address when replying by email. |
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