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Linear power supply chokes
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John B:
I was doing some simulations for a linear power supply and was thinking about the peak currents and conduction angle through the bridge rectifier. In this case it's just a basic 50Hz transformer, full wave rectified and fed into about 24mF of filter caps. Naturally this makes the current pulses through the transformer short and sharp, so I experimented adding an inductor of around 10-25mH between the positive of the bridge rectifier and the main filter bank. Although the current waveform is distorted, as the inductance of the choke is increased, the peak current flowing through the transformer approaches the DC current at the output of the filter caps.

While I can find a few references, it doesn't seemed to be used that much in a linear context, that is, the choke being used as an energy storage device along with the caps.

So when and where is it worth bothering with? I've wound a 20mH inductor with 1mm wire for use.

Pros:
Peak current through diodes and transformer is reduced.

Cons:
Adds impedance and so the maximum DC current is reduced compared to capacitors alone.

Anything else to add?
ledtester:
If I understand it correctly, this information from Hammond Manufacturing suggest that adding an inductor will increase the DC current capacity over just using a capacitor:

http://www.hammondmfg.com/pdf/5c007.pdf
John B:
Yep, what I'm talking about is like the last example "Full Wave Bridge Input Load", but for a given resistive load, an increase in choke inductance results in less ripple, but a lower DC voltage compared to caps alone.
IanB:
It seems the choke + capacitor arrangement was (commonly?) used in HV DC supplies for valve/vacuum tube equipment, but was apparently not adopted or considered necessary for low voltage supplies. Maybe because the LV supplies usually have a voltage regulator for ripple rejection, while this was absent in the HV supplies.

Although a filter choke may may allow a smaller transformer to be used, that must be traded off against the size and weight of the choke. It may be that the trade-off isn't worth it.
SeanB:
Choke on valve HT was there for higher anode current applications, as rectifier tubes really do not have a very good overload characteristic, and have very poor pulse rating compared to a silicon rectifier diode. Thus the choke, to reduce peak pulse currents, and thus losses across the rectifier, and as a bonus lower ripple on the supply lines, so the poor power supply ripple rejection of the amplifier was not going to introduce hum with high ripple voltage. Remember on valves the other grids are also connected nearly directly to the power rail with almost no decoupling. Valve rectifier anode drop is current dependent, and even a small rise in current leads to a very much hotter running anode, and as they typically ran at 500C at full rated current, just a small increase could get them to 800C where they glowed visibly red, and then they would start to have secondary emission, go into thermal runaway and kill both the rectifier tube and the power transformer.

On lower voltage higher current supplies the choke however gets very big very fast, in fact the best way to have a choke power supply is to design it into the power transformer, making it larger, thicker wire and have some leakage inductance in it. Thus the ferroresonant transformer, which can have a pretty low ripple supply voltage at a very high current, and as a bonus the conduction angle of the diodes is very large, as the high harmonic distortion of the output makes it a more trapezoidal waveform than a sine wave. Added bonus it is self limiting current wise as it will tend to be a constant power over a certain current, but under that is is relatively constant voltage.

They made great wet cell battery chargers, as they were able to charge a fully discharged bank without any attention, and would float the cells once charged. Only disadvantage was they ran hot at high power, and had a fixed no load dissipation that could be a good part of the full load rating.
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