I'm looking to build a mains filter for one of my systems based on the Fo-Felix design I found here.
Now, I had this idea about adding an indicator for each output, to show if a device is connected and drawing power. Bit by bit I researched my way into current sensing transformers and figured that I could use one, coupled with a transistor, to drive a white LED on the front panel. Making it go on/off would be relatively easy, but I decided to make this into a learning project as well, so why not make it vary its intensity with the current draw as well?
With the help of a friend I put together this schematic in LTSpice and it seems to do what I want: drive the LED at about 4mA for 0.1mA of transformer current and at 40mA for 1mA input (assuming 1:1000 transformer ratio, so mains draw would be 100mA -> 1A, the top end being mostly theoretical).
I'd be curious for some feedback on this, especially since I've gotten to a point where LTSpice will take "forever" to simulate the circuit if I change any value/part (so either spice is broken or there's something wrong with my circuit).
Now, I had this idea about adding an indicator for each output, to show if a device is connected and drawing power. Bit by bit I researched my way into current sensing transformers and figured that I could use one, coupled with a transistor, to drive a white LED on the front panel. Making it go on/off would be relatively easy, but I decided to make this into a learning project as well, so why not make it vary its intensity with the current draw as well?
With the help of a friend I put together this schematic in LTSpice and it seems to do what I want: drive the LED at about 4mA for 0.1mA of transformer current and at 40mA for 1mA input (assuming 1:1000 transformer ratio, so mains draw would be 100mA -> 1A, the top end being mostly theoretical).
I'd be curious for some feedback on this, especially since I've gotten to a point where LTSpice will take "forever" to simulate the circuit if I change any value/part (so either spice is broken or there's something wrong with my circuit).
A current transformer is normally loaded by a small value resistor. The small AC voltage across this resistor
would be then amplified and rectified by an active full wave rectifier op amp circuit. This removes the diode drops
from the process.
https://www.tutorialspoint.com/line...tegrated_circuits_applications_rectifiers.htm
would be then amplified and rectified by an active full wave rectifier op amp circuit. This removes the diode drops
from the process.
https://www.tutorialspoint.com/line...tegrated_circuits_applications_rectifiers.htm
on a 5/8 x 5/8 inch bobbin, i wind 2000 turns of #36 magnet wire and 2 turns #15 for primary, so then 1A primary current will drop 1 volt into a 1k ohm 2W resistor. maybe arduino can display the actual current readings...
Thanks, rayma! That was a very informative article. However, if I understood it correctly, it only handles the rectification part. It seems to have better performance, but at the expense of a dual op-amp and 2 diodes for the full wave (versus a simple bridge in my schematic). Not sure it's worth the trouble, to be honest, but I am glad I learned something new.
I'm pretty sure an Arduino could read the voltage, but I was looking for a simpler solution. However, I might go down this route, since I might need to produce a logarithmic output from a linear one and I could this in code.
It is possible to intercept the current using two schottky diodes, for minimal losses.
There is minimal processing, and no need for an auxiliary supply. Here is a working example (it has been in use for 15 years as a pilot light for my attic lighting):
This is the circuit before it is wrapped into a shrinking tube:
This is the circuit in operation (it operates from 5mA to 2A):
The autosynchronous rectifier can be much more elaborated: here is an example:
There are infinite variations possible on the rectifier and the converter, like this one:
There is minimal processing, and no need for an auxiliary supply. Here is a working example (it has been in use for 15 years as a pilot light for my attic lighting):
This is the circuit before it is wrapped into a shrinking tube:
This is the circuit in operation (it operates from 5mA to 2A):
The autosynchronous rectifier can be much more elaborated: here is an example:
There are infinite variations possible on the rectifier and the converter, like this one:
An alternative to a special transformer would be to use an optocoupler to isolate the signal.
It would probably need some changes to the rest of the circuits as well, but that should be straight forward.
Jan
It would probably need some changes to the rest of the circuits as well, but that should be straight forward.
Jan