M
mkr5000
I have a simple circuit on a breadboard that has been doing fine 24/7 for months which is --
120vac, hot into a 200k 1/2 watt that feeds a dropping cap (.47uf, 400v) that then feeds a bridge rectifier. The output of the bridge has a zener and a filter cap which supplies my DC.
I breadboarded it because I really never used a transformerless design in a project and just wanted to see how reliable it was. (so far -- very reliable).
My question is about the 100 ohm resistor (or around there) that is used in the neutral leg of the AC feeding the bridge that you often see in this circuit.
I'm not using one, just tying the neutral directly to the bridge.
So what is the purpose of this resistor? A safety precuation? Just to provide "some" isolation from ground (neutral 120vac?) Or maybe it acts as a cheap fuse?
Of course, you'd be stupid to not have the ground isolated from the chassis or anything that you could touch (like they did in the 50's and 60's).
I'll have to say that it's been very reliable on the breadboard anyway -- but I'm only drawing 25ma or so with my load.
120vac, hot into a 200k 1/2 watt that feeds a dropping cap (.47uf, 400v) that then feeds a bridge rectifier. The output of the bridge has a zener and a filter cap which supplies my DC.
I breadboarded it because I really never used a transformerless design in a project and just wanted to see how reliable it was. (so far -- very reliable).
My question is about the 100 ohm resistor (or around there) that is used in the neutral leg of the AC feeding the bridge that you often see in this circuit.
I'm not using one, just tying the neutral directly to the bridge.
So what is the purpose of this resistor? A safety precuation? Just to provide "some" isolation from ground (neutral 120vac?) Or maybe it acts as a cheap fuse?
Of course, you'd be stupid to not have the ground isolated from the chassis or anything that you could touch (like they did in the 50's and 60's).
I'll have to say that it's been very reliable on the breadboard anyway -- but I'm only drawing 25ma or so with my load.