Back when there were such things as "swinging chokes" (the name sounds like a now cringe reference to the mid 1960s) they would make chokes specially for choke input use with a slightly larger amount of copper (more turns), a slightly lesser amount of iron, and a big air gap. These would vary lots in inductance with DC current, but would hopefully maintain enough inductance to still be "choke input filters" at low currents, and would sacrifice inductance at higher currents. The larger air gap flattened the B/H curve to allow peak currents to stay not-too-far into the saturation region.
If one wanted to use modern commercially available ("smoothing", love that) chokes at higher AC voltages, a couple could also be connected in series. Or, if in hand, could be given the rayma test: hang one across an isolated (for safety, but it's still obviously dangerous to touch) mains AC voltage. If it stays cold and quiet, it's still an inductor. An isolated Variac is endlessly useful for DIY.
All good fortune,
Chris
If one wanted to use modern commercially available ("smoothing", love that) chokes at higher AC voltages, a couple could also be connected in series. Or, if in hand, could be given the rayma test: hang one across an isolated (for safety, but it's still obviously dangerous to touch) mains AC voltage. If it stays cold and quiet, it's still an inductor. An isolated Variac is endlessly useful for DIY.
All good fortune,
Chris
I remember the input was the swinging and the 2nd was the smoothing. Because of the saying: the swinger is a smoothy. Of course there was a time they were called bucker and booster as well..
Apparently, some Hi Fi / Stereo designers have no clue about the drastic change of B+ current of a CW transmitter:
Key-up Open (No current in the output tube), to Key-down Closed (Full current in the output tube).
Try that on a Full Gallon (1 killo Watt) CW transmitter amplifier.
Surprise, those transmitters used Swinging Chokes!
Tube Hi Fi / Stereo amplifiers are different than CW transmitters.
Advantages of choke input B+ on audio tube amplifiers, instead of using cap input filters:
Cooler power transformers for the same DC B+ current.
Better voltage regulation versus load current
Power Factors up to 0.9 (Which might even pass Europes power factor requirements).
More DC output current capability for vacuum tube rectifiers
Less voltage drop for vacuum tube rectifiers
Just my opinions, and experiences
Until I read some bad words about choke input power supplies, I had no idea they were so problematic.
I had no idea I was designing tube amplifiers that are just like the 1930s Tacoma Narrows Bridge.
Key-up Open (No current in the output tube), to Key-down Closed (Full current in the output tube).
Try that on a Full Gallon (1 killo Watt) CW transmitter amplifier.
Surprise, those transmitters used Swinging Chokes!
Tube Hi Fi / Stereo amplifiers are different than CW transmitters.
Advantages of choke input B+ on audio tube amplifiers, instead of using cap input filters:
Cooler power transformers for the same DC B+ current.
Better voltage regulation versus load current
Power Factors up to 0.9 (Which might even pass Europes power factor requirements).
More DC output current capability for vacuum tube rectifiers
Less voltage drop for vacuum tube rectifiers
Just my opinions, and experiences
Until I read some bad words about choke input power supplies, I had no idea they were so problematic.
I had no idea I was designing tube amplifiers that are just like the 1930s Tacoma Narrows Bridge.
Warning,if you saturate your choke input choke, it no longer is a choke but a coil of wire. This leads to b+ going from 0.9 of rms ac input to 1.4 times vac rms input. Leads to big problems so treat with caution.
Hello,
In the past i had some chokes made at a local company. Back then if you would ask for a 80 mA probably it would work just as well with 100 mA.
Because they would not save on material to cut costs.
Even could use them for choke input.
Then i bought some Tango chokes designed for choke input. Surely better but 4 times more expensive in Japan.
Then bought some Lundahls, better than Tango and cheaper.
Greetings Eduard
In the past i had some chokes made at a local company. Back then if you would ask for a 80 mA probably it would work just as well with 100 mA.
Because they would not save on material to cut costs.
Even could use them for choke input.
Then i bought some Tango chokes designed for choke input. Surely better but 4 times more expensive in Japan.
Then bought some Lundahls, better than Tango and cheaper.
Greetings Eduard
In practice, a choke doesn't saturate abruptly. In order to increase the multiplication factor from 0.9 to 1.4, you need to saturate the choke via Bac increase, but not Bdc. If Bdc of a choke is exceeded, inductance begins to drop, but critical current increases too. The more critical current is increased, the lower the inductance needed in a linear way. These are swinging chokes. They retain the 0.9 voltage reduction of a critical choke, but they get lower inductance with higher current demand.
To achieve the 0.9 to 1.4 ramp up, Bdc needs to be none or constant, while changing Bac. This can be achieved by placing the choke before the rectifier.
To achieve the 0.9 to 1.4 ramp up, Bdc needs to be none or constant, while changing Bac. This can be achieved by placing the choke before the rectifier.
I think that what you are saying is that inductance does not actually decrease (because it's a linear function of the slope of the B/H curve) until after the B/H curve has crested. If manufacturers would publish actual B/H curves, a whole lot of this ambiguity would vanish.
All good fortune,
Chris
All good fortune,
Chris
I meant that when you reach the knee of a certain BH curve via Bdc, where permeability drops and inductance begins to drop, this automatically keeps Bdc from further increase, because Bdc = Idc * L / Turns * Afe. It remains somewhat at an equilibrium point. The inductance begins to swing with changing Idc demands, but the 0.9 voltage factor remains the same, because critical current is also linear in terms of L and Idc.
I haven't documented this, but measured it in a few projects involving class AB SS amplifiers with LC filter swinging chokes with little to no airgap. For an LM1875 chip amplifier for example, I kept the inductance of the choke at 0.5H to maintain critical inductance for idle current draw. The 0.9 factor would be maintained until full power.
I haven't documented this, but measured it in a few projects involving class AB SS amplifiers with LC filter swinging chokes with little to no airgap. For an LM1875 chip amplifier for example, I kept the inductance of the choke at 0.5H to maintain critical inductance for idle current draw. The 0.9 factor would be maintained until full power.
It's an old (small signal) measurement- as sample-: inductance versus Idc.
As you can see, the -large- 1.5H/100mA choke's inductance almost static until the current below the granted current. Over it starts to decrease.
As you can see, the -large- 1.5H/100mA choke's inductance almost static until the current below the granted current. Over it starts to decrease.
That swinging choke isn’t the only source of inductance in your power supply. Eventually, you will run out of inductance in the choke. But the transformer’s leakage reactance is and always will be there, no matter how much current you draw. That series inductance will NOT saturate. With the way they undersize transformers in consumer audio (and a lot of pro audio) these days the rail voltages drop to some 65-70% of the unloaded voltage when running to full power. Resistance will not come close to accounting for this drop - at the typical 4 to 8 X overload, the transformer itself is flywheeling. You’ve GOT critical inductance at full power. You just don’t have it at “normal” current draw. Put in enough swing choke to cover down to quiescent, even if it saturates out hard at full power, and you effectively have a full choke input supply.
If you are really looking to exploit this, a split secondary (high isolation) EI transformer is the way to go. They’ve got 20% regulation figures at full typical load - even the big 2kW ones. Less inductor is therefore required to GET to critical inductance.
If you are really looking to exploit this, a split secondary (high isolation) EI transformer is the way to go. They’ve got 20% regulation figures at full typical load - even the big 2kW ones. Less inductor is therefore required to GET to critical inductance.
It depends on what effect you're looking for.
Transformer leakage inductance serves the only purpose of reducing capacitor charge ripple current. But being located before the rectifier, it doesn't contribute to the choke input effect to mantain rectified voltage at 0.9 factor. A high leakage transformer will worsens regulation effect at high current draws.
Transformer leakage inductance serves the only purpose of reducing capacitor charge ripple current. But being located before the rectifier, it doesn't contribute to the choke input effect to mantain rectified voltage at 0.9 factor. A high leakage transformer will worsens regulation effect at high current draws.
Hello,
All chokes are equal but some chokes are more equal than others haha.
Recently i was a bit involved in looking for a choke to be used in a choke input supply for a circuit that was pulling around max 45 mA including the current needed to assure choke input conditions all the time.
The original design was a clc design using a 5 H choke at 20 ohm dcr but after the choke a serious big cap 39000 microfarad.
We found a 20H input choke with 60 ohm dcr that took rather long time to fill up the cap but ripple ended up really nice.
Lundahl offers the possibility to get choke with adjusted airgap to get less current rating and higher Henry number instead. A higher current rated choke needs more iron and thicker wire. This way we could end up with a more than 20 Henry choke with less than 3 ohm dcr.
Going from 60 ohm to 3 ohm is a big advantage i guess.
There were some cheaper options too like 10H at 15 ohm or 8H at 9 ohm where i would say the benefit of a much lower dcr will give more benefits than the two extra H.
The supply being for a solid state preamp and no tube rectifier lower dcr could be more important than we think
I think that a quality choke is a good investment. I have heard a few ones and i can assure that a bigger choke will give you more profit than a bigger power transformer. I mean with a choke input supply.
Greetings.Eduard
All chokes are equal but some chokes are more equal than others haha.
Recently i was a bit involved in looking for a choke to be used in a choke input supply for a circuit that was pulling around max 45 mA including the current needed to assure choke input conditions all the time.
The original design was a clc design using a 5 H choke at 20 ohm dcr but after the choke a serious big cap 39000 microfarad.
We found a 20H input choke with 60 ohm dcr that took rather long time to fill up the cap but ripple ended up really nice.
Lundahl offers the possibility to get choke with adjusted airgap to get less current rating and higher Henry number instead. A higher current rated choke needs more iron and thicker wire. This way we could end up with a more than 20 Henry choke with less than 3 ohm dcr.
Going from 60 ohm to 3 ohm is a big advantage i guess.
There were some cheaper options too like 10H at 15 ohm or 8H at 9 ohm where i would say the benefit of a much lower dcr will give more benefits than the two extra H.
The supply being for a solid state preamp and no tube rectifier lower dcr could be more important than we think
I think that a quality choke is a good investment. I have heard a few ones and i can assure that a bigger choke will give you more profit than a bigger power transformer. I mean with a choke input supply.
Greetings.Eduard
Ah, so this is a concern for a limiting condition around the saturation values of B? It's easy to assume that there is a "critical inductance", a nominal "minimal inductance" where the curve bends, and to the right of which "choke input" happens, a simple linear relation to an imaginary load resistance. Always seemed fine, if puzzling.
But, it seems you're asking is, what happens after (to the right) of saturation? If I've misread you, please correct me, because I'm very, very keen to learn from you.
All good fortune,
Chris
Exceeding Idc until to the knee [saturation] region of the BH curve starts bringing inductance down. However, inductance down vs ramping Idc tend to compensate each other in terms of retaining critical inductance, so the 0.9 factor remain. So a small choke can operate as a choke input filter over a big amount of current draws, but it becomes a swinging choke with a changing inductance. The drawback is that you get higher pulsating capacitor charging current with increased current draw, compared with a constant value inductor over the Idc working range.
A very closely related parallel subject to choke input filters is:
Air gapped single ended output transformers.
Check out:
"To Be, or Not To Be, Linear! 'The Single Ended Transformer' by Dr. Tom Hodgson.
"Sound Practices" magazine, Issue 10, Winter 1995
Part of the discussion is about the differences in the curves of non air-gapped push pull versus air-gapped single ended transformers.
There are lots of graphs to illustrate the factors of push pull and single ended transformers.
For those like myself who have built Parafeed output stages, the proper selection of a plate choke is important; but that is a thread for another day.
Air gapped single ended output transformers.
Check out:
"To Be, or Not To Be, Linear! 'The Single Ended Transformer' by Dr. Tom Hodgson.
"Sound Practices" magazine, Issue 10, Winter 1995
Part of the discussion is about the differences in the curves of non air-gapped push pull versus air-gapped single ended transformers.
There are lots of graphs to illustrate the factors of push pull and single ended transformers.
For those like myself who have built Parafeed output stages, the proper selection of a plate choke is important; but that is a thread for another day.