| jazz |
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!) |
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| jlsem |
| quote: | | 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. |
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 |
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| Sch3mat1c |
| quote: | Originally posted by jlsem
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 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.
| quote: | | The inductance of the choke swings with the current demand, decreasing when current demand goes up. |
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 |
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| jlsem |
| quote: | | 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. |
Swinging chokes are usually more expensive and harder to find than regular chokes. Where's the efficiency in that? Ordinary chokes swing a little bit anyway and for home audio, a bleeder resistor provides good enough regulation.
John |
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| Sch3mat1c |
Really? Then why are they used..
Tim |
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| jazz |
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 |
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| thoriated |
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. |
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