powering a 555 off mains

[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. 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.

 

[Franc Zabkar]

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.

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

 

[Phil Allison]

"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

 

[Franc Zabkar]

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

 

[Mark Harriss]

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.

 

[Mark Harriss]

I wondered if my post would bring you flapping out
of the woodwork of Nostradamus' coffin.

 

[Rheilly Phoull]

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

Hey Franc
Did ya get that lighting cct sorted ??

 

[Franc Zabkar]

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

 

[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.

FWIW, I see used MOSFET based (?) PWM treadmill DC motor controllers
(120V) on Ebay for US$60.

- Franc Zabkar