Yes, that's the purpose of the CM choke: high impedance for the differential signal (audio signal across the filament), but low impedance for the common signal.
Yes, they don't say anything about material permeability, which could vary from 10 to 150, with corresponding effect on inductance.
The stored energy of a 220mH inductor at 4Amps is Eind =0.5 * L * I² = 0.5 * 0.22 * 16 = ca 1.7J .
Fantastic!
About 1000 times bigger than the real cores I do know.
Please give a link to that calculation
It is a well known fact that the energy storage capabilities of a core of given size drops with increasing permeability. Hence Al-value is by far not the first number to look at when selecting a storage inductor core.
Micrometals iron powder catalog page 34:
Micrometals catalog
Graph in the right hand corner of the page gives the formula H=0.4 x pi x N x I / Le, where
H - magnetizing force, Oe;
N - number of turns, in this case 60.
I - DC current, A, 4.
Le - magnetic path length, cm, 6
With these numbers, H is approximately 48 Oe. On the graph find mu at this H, about 45% of initial. Multiply zero DC inductance of 440 uH by 0.45, get 198 uH.
Micrometals catalog
Graph in the right hand corner of the page gives the formula H=0.4 x pi x N x I / Le, where
H - magnetizing force, Oe;
N - number of turns, in this case 60.
I - DC current, A, 4.
Le - magnetic path length, cm, 6
With these numbers, H is approximately 48 Oe. On the graph find mu at this H, about 45% of initial. Multiply zero DC inductance of 440 uH by 0.45, get 198 uH.
So I took the formula of your link into a spreadsheet and this is what I calculate for 1, 50 and 60 turns.
As expected, the stored energy is independent of number of turns and with <2.5mJ well within expected range.
As expected, the stored energy is independent of number of turns and with <2.5mJ well within expected range.
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Or, 30 turns 0.25 mH 4 A. Two such inductors in series provide critical inductance for a pair of 2A3 filaments.
No, no , no, my bad, it was uH not mH. 500 uH (or 0.5 mH) is the target value for the input choke.
But what do you intend to filter with 500uH? Its impedance at 50Hz is about 0.15 Ohms
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This is not a smoothing choke. The purpose of the first choke in a choke input filter is to provide uninterrupted sinusoidal current in power transformer secondary and improve output voltage regulation. For this purpose the first choke must have at least the minimum inductance value, aka critical inductance. For 2.5 V 4 A, the critical value is about 0.4 - 0.5 mH. The impedance of the first choke at specific frequencies doesn't matter (if we disregard frequency-dependent change of inductance). Filtering should be regarded in conjunction with downstream elements, capacitors and smoothing chokes.
I could do it in PSUD2, but it doesn't have a choice for a pair of 10 A Ge diodes with CT transformer secondary. It would be easier to assemble the circuit and measure. It won't show transients though. Diodes will definitely need voltage and current protection, which I will discuss in a separate post.
Ge rectifier derating
Current rating of Ge rectifiers is at case temperature of 20 degrees C. From D305 data sheet, at 55 C case temperature, the maximum allowable current is 60% of the rated, or 6A. Dissipated power at 6A is 0.35 V x 3A = 1 W, so diodes must be on heat sinks. Case temperature should not exceed 60 C, otherwise there could be thermal runaway.
Current rating of Ge rectifiers is at case temperature of 20 degrees C. From D305 data sheet, at 55 C case temperature, the maximum allowable current is 60% of the rated, or 6A. Dissipated power at 6A is 0.35 V x 3A = 1 W, so diodes must be on heat sinks. Case temperature should not exceed 60 C, otherwise there could be thermal runaway.