Hi there,
For a while now i've been wondering: there's so much talk about choke input psu's and yes i can see the advantage and wanna try. However as far as i've understood one need's a 'swinging choke' for this. What's the difference between a swinging choke and a regular coil. That's given something like 250 volts/100mA. I just don't understand what makes an lc input combination function as a swingin
choke (rec bridge l/c) instead as a filter choke in a standard clc combo.
Any input?
Regards joris
(currently listening to katie melua's 'call of the search', which is a great album!)
For a while now i've been wondering: there's so much talk about choke input psu's and yes i can see the advantage and wanna try. However as far as i've understood one need's a 'swinging choke' for this. What's the difference between a swinging choke and a regular coil. That's given something like 250 volts/100mA. I just don't understand what makes an lc input combination function as a swingin
choke (rec bridge l/c) instead as a filter choke in a standard clc combo.Any input?
Regards joris
(currently listening to katie melua's 'call of the search', which is a great album!)
A swinging choke is only necessary when there are are large current swing requirements as in big class B amplifiers and class C transmitters. The inductance of the choke swings with the current demand, decreasing when current demand goes up. You don't need a swinging choke on an audio amplifier, just a choke that is designed for choke input operation. Most military surplus potted chokes fit the bill.
John
jlsem said:
The requirements of large amplifiers are no different from that of a single 12AU7 in class B. It's just scale, you want to use a more weight- and cost-efficient swinging choke than a standard choke.
The point being you run it on the edge so as current goes up, inductance goes down along the regulation curve. So you get better voltage output, regulation and efficiency.
Tim
Hi there,
so given the above comments i should be fine when using a standard choke in a lclc configuration. For example: 200v input 10H/200mA (EIcore 100r dc), 120uF, 10H/200mA (ei core 100r dc), 120uF. Which simulates to sometihing like a nice and steady 185 volts output, giving me just about the headroom for the regulater to put out something like 150V @ 50Ma?
Only when i'm trying to make a power beast in class c or b and want to save on parts a specific swinging choke would be needed. And even then, given availability, a standard ei core choke with adequate ratings should do the job? And given the fluctuating currents in this case, a very big and rather low value bleeder resistor should equalize things out. Which would then reduce effeciency and hence equalize the cost benefit.
So is it save to say that as long as the values for the choke are correct and give some margine. a standard choke will be just as adequate as a swinging choke. That is given the better availability of standard ei core chokes like mentioned above. Hence this is what is mostly used?
regards
Joris
so given the above comments i should be fine when using a standard choke in a lclc configuration. For example: 200v input 10H/200mA (EIcore 100r dc), 120uF, 10H/200mA (ei core 100r dc), 120uF. Which simulates to sometihing like a nice and steady 185 volts output, giving me just about the headroom for the regulater to put out something like 150V @ 50Ma?
Only when i'm trying to make a power beast in class c or b and want to save on parts a specific swinging choke would be needed. And even then, given availability, a standard ei core choke with adequate ratings should do the job? And given the fluctuating currents in this case, a very big and rather low value bleeder resistor should equalize things out. Which would then reduce effeciency and hence equalize the cost benefit.
So is it save to say that as long as the values for the choke are correct and give some margine. a standard choke will be just as adequate as a swinging choke. That is given the better availability of standard ei core chokes like mentioned above. Hence this is what is mostly used?
regards
Joris
I believe this is largely the case. A minimum DC load needs to be always imposed on a swinging choke input supply, or else the DC output voltage given a sine wave AC input will rise by up to 40% when the effective load resistance starts to approach or exceed that of the low current reactance of the swinging choke which could create all sorts of problems with circuits that use components close to their voltage limits as well as losing any sort of regulation at lighter loads.
That said, IMO, a properly applied swinging choke is a pretty neat way to get output stage power supply load regulation for a class AB power amp without adding any active components.
That said, IMO, a properly applied swinging choke is a pretty neat way to get output stage power supply load regulation for a class AB power amp without adding any active components.
Hi all,
Excuse me to have resurrected this old thread!
I am learning about chocke input PSU.
I have read the chocke is very stressed and will produce very fastidious noise-vibration thus it is necessary it is designed expressly to work in this special application.
Second, normally a parallel resistor ( bleeder?) is always required
third , a series RC in parallel to the chocke can save from high tension peak.
What is method to calculate the parallel resistor ohm value?
Can you suggest a good" brand" for those special chockes , possibily
in europe ?
Cheers,
Paolo
Excuse me to have resurrected this old thread!
I am learning about chocke input PSU.
I have read the chocke is very stressed and will produce very fastidious noise-vibration thus it is necessary it is designed expressly to work in this special application.
Second, normally a parallel resistor ( bleeder?) is always required
third , a series RC in parallel to the chocke can save from high tension peak.
What is method to calculate the parallel resistor ohm value?
Can you suggest a good" brand" for those special chockes , possibily
in europe ?
Cheers,
Paolo
A swinging choke is desirable in input-choke supplies where the current demand is highly variable.
The reason is simple: an input choke filter works only if the L value is greater than a critical value.
Such critical value for the inductance is given by the load divided by 6*pi*f (where f is 50 or 60 Hz depending on where you live!).
If the inductance is less than its critical value the LC filter will work as a simple RC filter where R is the DC resistance of the choke.
In a class B amplifier amplifier, for example, the idle current is much lower than the anode current at max output.
So if one uses a choke that works at max output only it could not work properly at lower power output.
Instead if one chooses the choke with high inductance value it could be very big and expensive (to work also with much higher currents).
One way to guarantee the minimum load for an effective L-input filter is using a bleeder resistor. However this is not always cost effective or possible.
Let's consider a 108W class B EL34 PP (penthode connection).
The anode voltage is 800V and the idle current is 2x20mA.
The current at max output, for 11K a-a load, will be approx. 2x100 mA.
For simplicity, let's assume other series resistances to be zero.
Consider 50 Hz AC line so that 6*pi*f = 942.5 1/s
Load = 800V/200mA = 4K
The critical value at max output will be: L = 4.32 H
It is a good rule to use a higher value than critcal, say twice.
Anyway if we use 8.64 H/ 200mA standard choke it will be below the critical value for lower output.
At 10W output, for example, the anode current will be 2x30 mA and the input choke critical value would be: 14.1 H!!
So, there will be no effective input choke!
Cheers,
45
The reason is simple: an input choke filter works only if the L value is greater than a critical value.
Such critical value for the inductance is given by the load divided by 6*pi*f (where f is 50 or 60 Hz depending on where you live!).
If the inductance is less than its critical value the LC filter will work as a simple RC filter where R is the DC resistance of the choke.
In a class B amplifier amplifier, for example, the idle current is much lower than the anode current at max output.
So if one uses a choke that works at max output only it could not work properly at lower power output.
Instead if one chooses the choke with high inductance value it could be very big and expensive (to work also with much higher currents).
One way to guarantee the minimum load for an effective L-input filter is using a bleeder resistor. However this is not always cost effective or possible.
Let's consider a 108W class B EL34 PP (penthode connection).
The anode voltage is 800V and the idle current is 2x20mA.
The current at max output, for 11K a-a load, will be approx. 2x100 mA.
For simplicity, let's assume other series resistances to be zero.
Consider 50 Hz AC line so that 6*pi*f = 942.5 1/s
Load = 800V/200mA = 4K
The critical value at max output will be: L = 4.32 H
It is a good rule to use a higher value than critcal, say twice.
Anyway if we use 8.64 H/ 200mA standard choke it will be below the critical value for lower output.
At 10W output, for example, the anode current will be 2x30 mA and the input choke critical value would be: 14.1 H!!
So, there will be no effective input choke!
Cheers,
45
inertial said:Hi all,
Excuse me to have resurrected this old thread!
I am learning about chocke input PSU.
I have read the chocke is very stressed and will produce very fastidious noise-vibration thus it is necessary it is designed expressly to work in this special application.
Second, normally a parallel resistor ( bleeder?) is always required
third , a series RC in parallel to the chocke can save from high tension peak.
What is method to calculate the parallel resistor ohm value?
Can you suggest a good" brand" for those special chockes , possibily
in europe ?
Cheers,
Paolo
The best way to know the resistance value to use for the RC series network in parallel with choke is to look at the transient current on the oscilloscope!
Theoretical values are usually 99% wrong.....that happens because there are unknown parasitic effects that you cannot account for.
It can be that the calculated value is 100 ohm while the optimal practical value is 10Kohm!!!
Cheers,
45
Thanks Douglas & 45
45, very appreciate explanation!
I know input chocke is much much more difficult than normal CL.
For my luck I have only to make a PSU for my 6N6P line-driver,
common cathode. I think the current is costant.
My problem is where to purchase a noise-less CHEAP chocke.
In Italy they are very very rare and expansive, to not talk about you really know if it is "silent" or not only after you have purchased....
Cheers,
Paolo
45, very appreciate explanation!
I know input chocke is much much more difficult than normal CL.
For my luck I have only to make a PSU for my 6N6P line-driver,
common cathode. I think the current is costant.
My problem is where to purchase a noise-less CHEAP chocke.
In Italy they are very very rare and expansive, to not talk about you really know if it is "silent" or not only after you have purchased....
Cheers,
Paolo
Just a few extra (practicel) remarks.
Swinging choke (less so ordinary) does a good regulating job when correctly calculated, BUT:
I have never been able to locate this on the same chassis as the amplifier without introducing some induced noise - admittedly in a high-current amplifier. Others members have commented on this as well. So it is advisable to try construct the amplifier first and then hold the choke in the vicinity at all attitudes to try to determine the best position.
Then, one must be careful of the voltages across such a choke (for that matter between the choke input terminal and earth). Rather like a motor car coil, very high spikes are generated every time the ac cycle goes past diode turn-off point. (Snubbers are sometimes used in parallel, consisting of a series R-C. Cs should be of the several KV type. Values that work are about 1,5 - 3uF and 2 - 4 k.ohms.)
Swinging choke (less so ordinary) does a good regulating job when correctly calculated, BUT:
I have never been able to locate this on the same chassis as the amplifier without introducing some induced noise - admittedly in a high-current amplifier. Others members have commented on this as well. So it is advisable to try construct the amplifier first and then hold the choke in the vicinity at all attitudes to try to determine the best position.
Then, one must be careful of the voltages across such a choke (for that matter between the choke input terminal and earth). Rather like a motor car coil, very high spikes are generated every time the ac cycle goes past diode turn-off point. (Snubbers are sometimes used in parallel, consisting of a series R-C. Cs should be of the several KV type. Values that work are about 1,5 - 3uF and 2 - 4 k.ohms.)
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