Mostly they are designed to not buzz so much when used as an input choke.
They may be designed as swinging chokes where they will have more inductance with a light load and have less inductance with a heavy load.
The point of the swinging choke is to just satisfy the minimum inductance number that is required for light loading.
They are designed to handle large amounts of AC ripple. The inductance is high at turn on, and drops as the load increases. It's important to note, however, that a choke-input supply must present a certain minimum load at turn on. You'll usually see a hefty bleeder resistor following the first cap, to provide something like 10-20mA minimum current at turn on.
Huh? We both said the same thing. High inductance with a light load, inductance drops as load increases. In my comment I guess I could clarify that by "turn-on" I meant the circuit tubes are not yet conducting and current ramps up as they do.As a long-time professional servicer, I know how and why chokes work, fortunately.
But these two comments would stun the hell out of somebody else.
Both sound like they contradict each other.
Thanks, that's a much better explanation than mine, and very helpful to me.Assuming you are talking about a line frequency choke input rectifier, a choke input prevents the high current pulses that a capacitor input rectifier creates. In a cap input circuit, the rectifiers only conduct for a short pulse at the sine wave peak and therefore the cap voltage charges to that voltage. An inductor input rectifier tends towards the average voltage instead of the peak voltage and the current tends towards conduction over the whole AC cycle. For an accurate prediction, you need to run a simulation in SPICE, including the output loading. Note that a choke input rectifier requires a current path (diode) for the off-cycle where the choke is discharging.
This is similar to the much smaller chokes used in PWM power supplies and class-D amplifiers, where the switching charges and discharges the output choke in a low amplitude triangular current wave centered on the DC or audio frequency average.
Yes I am , those are details and normal calculations , if you got a normal choke will work more or less perfect as input choke .Are you sure about that? See this post:
Really? Remember that in the tube heydays LC filtering was common especially with mercury filled rectifiers (80, 866 etc.). I've never seen an additional grounded diode there to »discharge« the choke.Note that a choke input rectifier requires a current path (diode) for the off-cycle where the choke is discharging.
The concern with choke input filtering is that the diodes undergo a 'hard' commutation
Choke input filters do not need a freewheeling diode - that function is provided by the other diode (in eg. a full-wave rectifier).