Hi folks,
I've been wondering, perhaps not in PSUD, but in LTSpice, is there a way to make a model of a saturating choke with the two following options:
1. Decreasing inductance vs DC current when used into a choke input filter, for the power supply of a class AB amplifier
2. Decreasing inductance vs AC voltage across the choke when used before the rectifier, same application.
I've been wondering, perhaps not in PSUD, but in LTSpice, is there a way to make a model of a saturating choke with the two following options:
1. Decreasing inductance vs DC current when used into a choke input filter, for the power supply of a class AB amplifier
2. Decreasing inductance vs AC voltage across the choke when used before the rectifier, same application.
You can define L as the product of L at zero bias times the current through a voltage source.
Something like .param Lbias = 100m * I(V2), then in your circuit define L value as {Lbias}.
Not sure that will scale during a simulation run or whether that becomes a fixed value during a sim run.
If the latter, you may have to do several runs with .step values for different bias currents.
@Mooly may have other/better suggestions.
Jan
Something like .param Lbias = 100m * I(V2), then in your circuit define L value as {Lbias}.
Not sure that will scale during a simulation run or whether that becomes a fixed value during a sim run.
If the latter, you may have to do several runs with .step values for different bias currents.
@Mooly may have other/better suggestions.
Jan
With a constant current on an inductant load it is different depending on the paper thickness for E+I, if it is too high inductance decreases and the alternating voltage measured at the filter output with a selective AC mV (100Hz) is high, the same and if the thickness is too small inductance decreases so the alternating voltage increases, basically there will be an optimal thickness for which the voltage AC isit's the smallest
Not really Jan, that sound like something very specialised.
I imagine you would need a real working circuit to measure its properties while trying to get the models right in simulation to match rather than just accepting what LT seems to tell you.
LTspice has (natively) a provision to simulate the non-linearities of a magnetic core.
I have used this option many years ago, but it is not simple to grasp, parametrize and use though.
I'll try to find a simulation example in my archives. There are probably tutorials about it on the net
I have used this option many years ago, but it is not simple to grasp, parametrize and use though.
I'll try to find a simulation example in my archives. There are probably tutorials about it on the net
I am asuming that the question is how to construct a model from known inductor properties.
If the OP does not have any data for his inductor, then of course LTspice is no help either - it needs the data for the model.
Jan
If the OP does not have any data for his inductor, then of course LTspice is no help either - it needs the data for the model.
Jan
I didn't manage to locate my examples so far, in the mean time here is the example provided in LTspice:
And here is a tutorial:
https://www.allaboutcircuits.com/technical-articles/modeling-inductors-with-ltspice/
There are many others
https://www.allaboutcircuits.com/technical-articles/modeling-inductors-with-ltspice/
There are many others
50AE,
From your Post # 1
Why would you put a choke Before the rectifier?
Perhaps I misunderstood what you said.
From your Post # 1
Why would you put a choke Before the rectifier?
Perhaps I misunderstood what you said.
Thank you, folks. Good info as a start!
6A3s, usually, If one places a saturating choke before the rectifier, my idea is as follows.
-At low amplifier quiescent current, the choke will not saturate and has full inductance value.
-During increasing current draw, the voltage drop across the choke will increase.
-Assuming the choke will be designed to saturate above a certain voltage drop across it, it will begin to saturate, countering the voltage drop and bringing regulation to the power supply.
Why the reason I'd try it, compared to a traditional input choke after the rectifier?
1. The swinging choke has a high inductance at low current demands to satisfy critical inductance and requires huge, tens of mF to dampen the ringing.
2. Dampening via series resistance kills regulation capability. Not an option.
3. A choke after the rectifier cannot regulate above a 0.9 factor Vdc/Va factor, because DC choke saturation and critical inductance are both linear and cancel each other. I have also tested it practically with a swinging choke input on my LM1875 amplifier.
4. However I am not certain by any means that a choke before the rectifier will regulate better, but it might be worth trying.
6A3s, usually, If one places a saturating choke before the rectifier, my idea is as follows.
-At low amplifier quiescent current, the choke will not saturate and has full inductance value.
-During increasing current draw, the voltage drop across the choke will increase.
-Assuming the choke will be designed to saturate above a certain voltage drop across it, it will begin to saturate, countering the voltage drop and bringing regulation to the power supply.
Why the reason I'd try it, compared to a traditional input choke after the rectifier?
1. The swinging choke has a high inductance at low current demands to satisfy critical inductance and requires huge, tens of mF to dampen the ringing.
2. Dampening via series resistance kills regulation capability. Not an option.
3. A choke after the rectifier cannot regulate above a 0.9 factor Vdc/Va factor, because DC choke saturation and critical inductance are both linear and cancel each other. I have also tested it practically with a swinging choke input on my LM1875 amplifier.
4. However I am not certain by any means that a choke before the rectifier will regulate better, but it might be worth trying.
When the retifier opens up, there is a large current pulse to recharge the capacitor in a short time.
I think an inductor before the cap, after the rectifier, will always saturate independent of the amplifier current draw.
But I can be wrong; best to check this in LTsopice.
Jan
I think an inductor before the cap, after the rectifier, will always saturate independent of the amplifier current draw.
But I can be wrong; best to check this in LTsopice.
Jan
Jan,
In a choke input filter, the choke experiences 50% of the secondary transformer voltage 2x the frequency as voltage swing flux density, and the rest goes to DC flux density.
In a choke input filter, the choke experiences 50% of the secondary transformer voltage 2x the frequency as voltage swing flux density, and the rest goes to DC flux density.
In AC, the saturation is determined by the Volt*second product seen by the inductor, not by the current draw. Of course, as the current increases, the V*s product will increase, but I don't think that the effect will match that of a post-rectifier choke. In AC, the choke will be reset twice per cycle, taking it out of saturation for a moment, unlike the DC situation where the choke remains continuously saturated once the critical current is reached.
Obviously, these are theoretical considerations, and nothing replaces a practical experimentation. In addition, the AC mode might bring unforeseen benefits in some cases
It looks like LTSpice can plot the B-H locus for a steady-state set of operating conditions?
For a swinging choke, that locus should plot as a near vertical oriented loop close to the origin for low DC current operating conditions (ie. high incremental inductance), and as a more horizontal oriented loop as the loop moves further away from the origin for higher DC current operating conditions (ie. lower incremental inductance). With the relatively large AC voltage across the choke for choke input configuration, it would require the minimum/critical DC current (say 5-15% of DC current rating) to keep the BH loop away from passing through the origin every cycle (ie. where the loop would become quite abnormal in shape).
For a swinging choke, that locus should plot as a near vertical oriented loop close to the origin for low DC current operating conditions (ie. high incremental inductance), and as a more horizontal oriented loop as the loop moves further away from the origin for higher DC current operating conditions (ie. lower incremental inductance). With the relatively large AC voltage across the choke for choke input configuration, it would require the minimum/critical DC current (say 5-15% of DC current rating) to keep the BH loop away from passing through the origin every cycle (ie. where the loop would become quite abnormal in shape).
I am having trouble understanding the actions of a choke before the rectifier.
Too tired to think clearly.
Not sure I can see any advantage.
Please consider which choke you will use:
1. All E's on one side of an air gap, and all I's on the other side of that air gap.
Or,
2. No air gap, and all E's and all I's Interleaved (alternate E, I, E, I, etc.).
You will need two completely different simulation models of chokes, to simulate the results.
Probably not very many simulation software users have a model for the Non-Air-Gapped choke.
Have fun with that one.
Too tired to think clearly.
Not sure I can see any advantage.
Please consider which choke you will use:
1. All E's on one side of an air gap, and all I's on the other side of that air gap.
Or,
2. No air gap, and all E's and all I's Interleaved (alternate E, I, E, I, etc.).
You will need two completely different simulation models of chokes, to simulate the results.
Probably not very many simulation software users have a model for the Non-Air-Gapped choke.
Have fun with that one.
Let's define two operation modes. Low current draw and high current draw.
At low current draw, the choke will work at slight saturation or at saturation threshold. It will remain the highest inductance point, allowing the highest voltage drop across the choke.
At higher current draws, more voltage drop will try to occur at the choke, increasing the point of saturation, bringing the inductance down, resulting into lower voltage drop across it. That will increase the voltage at the transformer's primary, compensating for the higher current draw.
At low current draw, the choke will work at slight saturation or at saturation threshold. It will remain the highest inductance point, allowing the highest voltage drop across the choke.
At higher current draws, more voltage drop will try to occur at the choke, increasing the point of saturation, bringing the inductance down, resulting into lower voltage drop across it. That will increase the voltage at the transformer's primary, compensating for the higher current draw.
OK,
Knowledgeable Simulation Software fans . . .
Please get to work and help 50AE.
There should be a very large difference of Jazz playing on a Class A Single Ended amplifier,
Versus . . .
A 1 minute sustained 32Hz pipe organ note, that is played at near clipping on a Class AB push pull amplifier.
Knowledgeable Simulation Software fans . . .
Please get to work and help 50AE.
There should be a very large difference of Jazz playing on a Class A Single Ended amplifier,
Versus . . .
A 1 minute sustained 32Hz pipe organ note, that is played at near clipping on a Class AB push pull amplifier.