Looked at the various common mode links provided when I asked to start a new Thread.
This one gets close to what I need:
http://www.diyaudio.com/forums/tubes-valves/104578-common-mode-choke-question.html#post1255023
But I don't quite follow the explanation.
I want to try Galo's method for PSU using a common mode choke between the bridge rectifier and the smoothing capacitance.
The choke is the toroid type.
I can wind any thickness of wire from 0.3mm (too low current capability) to 3mm (hard to bend around the core).
I'm thinking of using 1.2mm or 1.4mm diameter enameled copper.
Once I have the two windings on the core, how do I check that I am wiring it in correctly?
Is there a way to "test" that it is wired as a common mode choke?
This one gets close to what I need:
http://www.diyaudio.com/forums/tubes-valves/104578-common-mode-choke-question.html#post1255023
But I don't quite follow the explanation.
I want to try Galo's method for PSU using a common mode choke between the bridge rectifier and the smoothing capacitance.
The choke is the toroid type.
I can wind any thickness of wire from 0.3mm (too low current capability) to 3mm (hard to bend around the core).
I'm thinking of using 1.2mm or 1.4mm diameter enameled copper.
Once I have the two windings on the core, how do I check that I am wiring it in correctly?
Is there a way to "test" that it is wired as a common mode choke?
Bifilar winding is the simplest way to check. Connect both 'starts' to the rectifier and both 'ends' to the capacitor. Bifilar is also the best way to ensure identical windings, which are needed to ensure flux cancellation.
Assuming you can identify the two windings OK (e.g. with a meter) then there are only two ways to wire them for common mode: right and wrong. The wrong way will give you a differential-mode choke with very low DC saturation current.
One way to check is to short what you believe to be one end. Measure the inductance across the two wires at the other end. This should be very low. If not you have it wrong.
Assuming you can identify the two windings OK (e.g. with a meter) then there are only two ways to wire them for common mode: right and wrong. The wrong way will give you a differential-mode choke with very low DC saturation current.
One way to check is to short what you believe to be one end. Measure the inductance across the two wires at the other end. This should be very low. If not you have it wrong.
What if I have the two "halves" of the toroid separated by a physical barrier.
A winding around one half and the second winding around the other half.
Can you talk me through the identification of the correct and wrong wiring?
A winding around one half and the second winding around the other half.
Can you talk me through the identification of the correct and wrong wiring?
When you say "short...one end" do you mean connect the two windings in series?
OK,
I can measure the inductance of a single winding.
Then series connect the two windings.
If the inductance has gone up to double or even quadruple that single value then it is wired wrong.
If the inductance goes down a "lot", then I have wired it correctly for common mode.
Now, how do I wire it into the two rails between the bridge rectifier and the smoothing caps?
Let's call/label the ends
a is the input common to both inductance tests.
b is the output of the first test
c is the end that gets connected to be ready for the second test.
d is the output of the second test.
I can measure the inductance of a single winding.
Then series connect the two windings.
If the inductance has gone up to double or even quadruple that single value then it is wired wrong.
If the inductance goes down a "lot", then I have wired it correctly for common mode.
Now, how do I wire it into the two rails between the bridge rectifier and the smoothing caps?
Let's call/label the ends
a is the input common to both inductance tests.
b is the output of the first test
c is the end that gets connected to be ready for the second test.
d is the output of the second test.
Take a choke which has just passed the common-mode test (i.e. two connections joined, low inductance between the other two connections). Put the first two connections (now separated) as the input from the rectifier. Put the other two connections (across which you did the measurement) as the output to the caps. Use an ohmmeter to get the polarity right.
Having said all that, I am not at all convinced of the benefit of common-mode chokes in power supplies, except as a mains filter. I suspect they are just a fad. They do nothing for smoothing (as ripple is differential mode) and rectifier spikes are likely to be mainly differential too.
Having said all that, I am not at all convinced of the benefit of common-mode chokes in power supplies, except as a mains filter. I suspect they are just a fad. They do nothing for smoothing (as ripple is differential mode) and rectifier spikes are likely to be mainly differential too.
Agreed: a CMC can play its role (useful or not) only if it manages to isolate all common mode paths.
If it is used with the usual center-tap/dual-supply configuration, the most obvious common-mode path, GND to the center tap is excluded and won't be isolated. A trifilar choke would be required (but I very much doubt it is worth the trouble).
I saw the sch in the Jung website in an article authored by Galo. part4 of regulators for high performance audio.
I thought it would be worth a try.
I do foresee a problem, the common mode requires balance of the DC current flows in the two halves of the choke.
If the Centre tap carries any current, then that "missing" current is not passing through one, or other, half of the balanced current choke.
This Centre tap current could result in saturation of the choke core.
A centre tapped is NOT what Galo shows in his PSU sch. He uses dual bridge on dual secondaries.
I thought it would be worth a try.
I do foresee a problem, the common mode requires balance of the DC current flows in the two halves of the choke.
If the Centre tap carries any current, then that "missing" current is not passing through one, or other, half of the balanced current choke.
This Centre tap current could result in saturation of the choke core.
A centre tapped is NOT what Galo shows in his PSU sch. He uses dual bridge on dual secondaries.
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