Hi All,
Does anyone have any idea of the minimum current needed for significant inductance from a choke. Say, for arguments sake, I wanted to use a choke with nominal ratings of 6H at max current of 60mA - what rough proportion of the max current would give me useable inductance for power supply filtering purposes? Thinking of using such a minibeast at around 6 to 8 mA (ie close to max ratings for use after 6H6 FW rectification - so I couldn't really supply it with much more current than this....)
Cheers,
Andrew.
Does anyone have any idea of the minimum current needed for significant inductance from a choke. Say, for arguments sake, I wanted to use a choke with nominal ratings of 6H at max current of 60mA - what rough proportion of the max current would give me useable inductance for power supply filtering purposes? Thinking of using such a minibeast at around 6 to 8 mA (ie close to max ratings for use after 6H6 FW rectification - so I couldn't really supply it with much more current than this....)
Cheers,
Andrew.
Thanks Tim,
I was hoping for such a reply! Mmmm 50 mA from a 6AL5 - more than I would have tried but what the heck!
The ratings for 6H6 are quite a bit lower than for 6AL5 - do you consider them to be overly conservative given that the 6H6 is not usually used for power rectification? (I currently use a pair of 6H6's in a FW bridge from a cheapo 12-0-12 tranny to supply negative grid bias in a CLC configuration for a stereo push-pull amp and am looking to do so for a single ended project which is almost complete). My concern is probably unfounded but I've been a bit concerned about the performance of a choke designed for larger currents (ie old relics from a wrecked radios - probably rated for around 60mA or so) at such low currents. However, based on your experience with the 6AL5, I'm feeling cheeky enough to try higher currents and see how it all performs..... The current amp performs well enough with the choke seeing around 8mA.... but maybe could be better....
Cheers,
Andrew.
I was hoping for such a reply! Mmmm 50 mA from a 6AL5 - more than I would have tried but what the heck!
The ratings for 6H6 are quite a bit lower than for 6AL5 - do you consider them to be overly conservative given that the 6H6 is not usually used for power rectification? (I currently use a pair of 6H6's in a FW bridge from a cheapo 12-0-12 tranny to supply negative grid bias in a CLC configuration for a stereo push-pull amp and am looking to do so for a single ended project which is almost complete). My concern is probably unfounded but I've been a bit concerned about the performance of a choke designed for larger currents (ie old relics from a wrecked radios - probably rated for around 60mA or so) at such low currents. However, based on your experience with the 6AL5, I'm feeling cheeky enough to try higher currents and see how it all performs..... The current amp performs well enough with the choke seeing around 8mA.... but maybe could be better....
Cheers,
Andrew.
It's rated for 330 PIV, 9mA or whatever per diode, so you can safely draw 18mA at 170VDC. My flyback was running maybe 100V, a far cry from 330V, so I can't comment on that rating. It was only a breadboarded circuit to which ratings do not apply, but heck, who cares-- 6AL5s are quite literally dime-a-dozen. Probably one or more e-Bay auctions right now selling a bag of them as xmas tree lights.
That said, I'd like to see what the true PIV is. If it goes as high as 500 or 800V, a bunch paralleled could be a cheap alternative to the 5Y3 and 6X4.
Tim
That said, I'd like to see what the true PIV is. If it goes as high as 500 or 800V, a bunch paralleled could be a cheap alternative to the 5Y3 and 6X4.
Tim
Datasheet says 10V @ 50mA. Not RMS so figure maybe 1/2 to 1/4 current to account for power factor. That means maybe 10V drop at 20-30mA from one tube!
Oh, since PIV is low and the cathodes are independent, a FW doubler would be better. That'll get you up to PIV volts out, instead of only half for a standard FW circuit.m Anyone for 300V at 100mA from five of these little things*?
*Why is bug-gers askeriskized anyway?
Tim
Oh, since PIV is low and the cathodes are independent, a FW doubler would be better. That'll get you up to PIV volts out, instead of only half for a standard FW circuit.m Anyone for 300V at 100mA from five of these little things*?
*Why is bug-gers askeriskized anyway?
Tim
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Joined 2009
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Andrew,
A query about minimum current for choke operation has to be put into the context of operation in a power supply. Design plots and equations have been around since Schade's time in the early 1940's, so it's pretty much find a technical book.
An answer depends on the filter, which in your case (and almost any other diy case) is an LC filter with R load.
So a design equation ends up with L, C, R and ripple frequency in it, and most equations/plots make use of ripple factor (rms AC ripple current in load / load DC current) - which is kind of important, as the L is there to give you a low ripple.
The load R is there, as it relates output dc voltage and dc current - so you also need to have a handle on both load voltage and current, and not just current.
I haven't come across a neat internet calculator, so if you have C and R as well as your L, or if you have a % ripple target and R, then some lookup charts etc can be quickly used.
You can also use PSUD2 simulation, although that requires you to have a transformer and diode and L, C and R in mind. But it does illustrate that lookup plots and equations (and simulations) often include approximations, like not specifically including winding or choke or diode resistances, or assuming choke inductance is what is written on the label.
A query about minimum current for choke operation has to be put into the context of operation in a power supply. Design plots and equations have been around since Schade's time in the early 1940's, so it's pretty much find a technical book.
An answer depends on the filter, which in your case (and almost any other diy case) is an LC filter with R load.
So a design equation ends up with L, C, R and ripple frequency in it, and most equations/plots make use of ripple factor (rms AC ripple current in load / load DC current) - which is kind of important, as the L is there to give you a low ripple.
The load R is there, as it relates output dc voltage and dc current - so you also need to have a handle on both load voltage and current, and not just current.
I haven't come across a neat internet calculator, so if you have C and R as well as your L, or if you have a % ripple target and R, then some lookup charts etc can be quickly used.
You can also use PSUD2 simulation, although that requires you to have a transformer and diode and L, C and R in mind. But it does illustrate that lookup plots and equations (and simulations) often include approximations, like not specifically including winding or choke or diode resistances, or assuming choke inductance is what is written on the label.
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I think the OP was wanting to know if a 6H 60mADC rated choke could be operated with a 6-8mA load current without adverse choke operation (ie. the choke current remains positive and continuous, and doesn't reach zero due to ripple).
This is equivalent to the typical query of what minimum bleed resistance (load current) is needed for a choke-input filtered power supply to maintain general voltage regulation during operation.
The simplified equation in post#11 is pretty much the same in many books. It is the most approximate form, and can be made more accurate by using equations that include smoothing capacitance, as well as series resistance from the secondary winding, diode and choke.
Another form of uncertainty is the choke inductance, which is rated at 6H at 60mAdc and probably some applied AC voltage (say 10Vrms). Typically the choke inductance will increase if the DC current reduces - that could well be 10-50% higher at say 10% of DC current rating. But incremental inductance will typically decrease when AC current is reduced (due to high load resistance), and that could easily counter the inductance increase for this bleeder load situation.
Some chokes, called swinging chokes, have an inductance that purposefully increases at low current levels. If the gap is visible in a typical choke with constant gap separation, then you can try and make your own swinging inductance characteristic by adding a steel lamination bridge across the choke gap.
This is equivalent to the typical query of what minimum bleed resistance (load current) is needed for a choke-input filtered power supply to maintain general voltage regulation during operation.
The simplified equation in post#11 is pretty much the same in many books. It is the most approximate form, and can be made more accurate by using equations that include smoothing capacitance, as well as series resistance from the secondary winding, diode and choke.
Another form of uncertainty is the choke inductance, which is rated at 6H at 60mAdc and probably some applied AC voltage (say 10Vrms). Typically the choke inductance will increase if the DC current reduces - that could well be 10-50% higher at say 10% of DC current rating. But incremental inductance will typically decrease when AC current is reduced (due to high load resistance), and that could easily counter the inductance increase for this bleeder load situation.
Some chokes, called swinging chokes, have an inductance that purposefully increases at low current levels. If the gap is visible in a typical choke with constant gap separation, then you can try and make your own swinging inductance characteristic by adding a steel lamination bridge across the choke gap.
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Perhaps he could tell us what he meant, as we now have two quite different understandings of his original question.
Is it a choke input PSU, or is the choke being used for ripple filtering in a cap input PSU?
Is the issue how the required minimum choke inductance (for choke input) varies with DC current draw, or how the inductance of a particular choke might vary with DC current?
Is it a choke input PSU, or is the choke being used for ripple filtering in a cap input PSU?
Is the issue how the required minimum choke inductance (for choke input) varies with DC current draw, or how the inductance of a particular choke might vary with DC current?
Clearly for me, inductance at no DC is at a maximum, given a core size, wire turns and gap size. Increasing DC from zero tends to saturate core giving less and less AxT for the AC component (as DC +AC amper-turns are added, or DC +AC flux density), thus reducing the inductance and then the impedance.
I seem to recall reading somewhere that for some OPTs a little DC current is needed to bias the core to get maximum inductance. I don't know whether that is true, or how widespread it is.
Anyway, he now may have answers to his question and answers to another question but we still don't know which is which.
Anyway, he now may have answers to his question and answers to another question but we still don't know which is which.
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I saw it in a Bob Mamanno work from TI, but didn't remember it exactly. The question is that when you start to increase magnetization in the core, what are you doing is align magnetic domains in the core. As you increment DC, you align more and more domains until saturation is found where almost all are aligned. But as you have some of them pre-alignated, then there are the possibility of move them in a direction or other by means of the AC flux. If no one or few of them are aligned, you only augment the disorder with the AC flux. If too many of them are aligned, then the difficulty to misalign them increases. This is in my own words, as simple as I can, and as I remember to had read.
Then, there is a grade of "order" of the magnetic domains that is easiest to manipulate, then more inductance.
Then, there is a grade of "order" of the magnetic domains that is easiest to manipulate, then more inductance.
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