Hello friends.
I have this zener follower regulator below and its input is 120 VAC; here in Canada that's the mains voltage. Although I do have a suitable transformer for it, for space and weight considerations it would be nice if I could dispense with it and hook up directly to the mains (ceramic fuse protected). I believe the correct term for such a connection is "in-line" ?.
Of course in that case the circuit ground above would not be tied to mains earth as that would shunt a diode at each half cycle, neutral and earth being tied at the distribution panel. This circuit feeds an ultrasonic vacuum tube heater supply that has an output transformer; so the business end will be isolated and grounded.
For safety and also EMI reduction, the whole contraption would be put in a grounded metallic case, which in turn would sit in the main amp enclosure, also earthed - Implementing class II double isolation. Not shown on schematic, discharge resistors across the caps both upstream and downstream of the pass mosfet would be placed for added safety.
So.............. What can go wrong right ?
As always, thanks in advance for any insights.
Joris
I have this zener follower regulator below and its input is 120 VAC; here in Canada that's the mains voltage. Although I do have a suitable transformer for it, for space and weight considerations it would be nice if I could dispense with it and hook up directly to the mains (ceramic fuse protected). I believe the correct term for such a connection is "in-line" ?.
Of course in that case the circuit ground above would not be tied to mains earth as that would shunt a diode at each half cycle, neutral and earth being tied at the distribution panel. This circuit feeds an ultrasonic vacuum tube heater supply that has an output transformer; so the business end will be isolated and grounded.
For safety and also EMI reduction, the whole contraption would be put in a grounded metallic case, which in turn would sit in the main amp enclosure, also earthed - Implementing class II double isolation. Not shown on schematic, discharge resistors across the caps both upstream and downstream of the pass mosfet would be placed for added safety.
So.............. What can go wrong right ?
As always, thanks in advance for any insights.
Joris
Definitely not, that is extremely dangerous. Always use an AC line isolation transformer.
Is that source not already grounded / earthed somewhere along 'the line', further up in your street?
Then, your pointing down triangle, sugggesting a 'safe' reference, is already at 60Vac. Not really safe I assume.
These kind of blindfolded shortcuts stems from opportunistic folks everywhere on the globe.
Rayma is right #2.
SomeJoe, do you have children?
My son is an adult now but I see your point. For what it's worth I build my designs with a key switch in series with the mains switch so nobody can power the amp if I'm not around.
Believe it or not, this ultrasonic heater supply I build is based on China-sourced halogen lamp "electronic transformers" which are not grounded nor isolated, sold with the intent to be mains-connected. The unit comes complete with bogus underwriter lab approval seals:
I guess I better not replicate this, but at least I didn't intent to sell any of these...
Thanks for your reply.
Mains transients (lightning, inductive load switching) can be several kV - directly connecting a supply like this will conduct these transients straight to the output. A transformer supply has the secondary earthed so transients can't appear at the output. Short differential transients will be soaked up by the filter caps on the secondary.
If you look at mains components you'll see their insulation ratings are measured in kV, not hundreds of volts as you might naively expect. Anything directly connected to the mains has to be able to handle these voltage transients.
And a CE marking with the wrong geometry (the geometry of a CE mark is precisely defined) such bogus marking is commonly referred to as "China Export".
I'll send you an appropiate flower arrangement, fresh from the Netherlands (we're the lowest country, most close to hell), when due...