[HomeBrew] Dual output power supply?

[N2EY@aol.com]

In a message dated 2/15/2004 6:27:28 PM Eastern Standard Time, n6kyr@netzero.com writes:

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> In a message dated 2/14/04 5:37:20 PM Eastern Standard Time, n6kyr@netzero.net writes:
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> Hi Jim:
> What is the reference for these calculations (that is, finding the suitability of the chokes in question)? 

Any ARRL Handbook from back in the GB days. 

Note that the "critical inductance in Henries is equal to or greater than load resistance in kilohms" rule ONLY applies to full-wave single-phase 60 Hz supplies. More inductance is needed with lower supply frequencies, and the use of choke input with half-wave is not recommended. You've already noted that the lowest ripple frequency in the output of a fullwave rectifier is twice the supply frequency, or 120 Hz.

I did the usual 2piFL calculations but it was way off (using 120 Hz after the rectifier as my "F" in the calc). Thanks. Cal, N6KYR. 

I know there is a rigid mathematical proof of the "one henry per K" rule, but I don't have it handy at the moment. Perhaps someone can check if the RCA Transmitting Tube manuals or the Radiotron Designer's Handbook has a more mathematical answer. I know it works because every HV power supply in the Southgate Type 7 is choke-input - and there are four of them..

73 de Jim, N2EY

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> snip>>OK, let's do the math.
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> If the HV choke is a 6-12 Hy swing choke, you need for the load resistance to never be less than 12,000 ohms. This means your load must never draw less than 45 mA at 540 volts in order to keep the output voltage from soaring. Also, the choke must have 12 Hy with 45 mA flowing through it. 
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> The 45 mA can be bleeder current, load current that is present all the time, or some combination. Dissipated power is 24.3 W, and if you are using resistors they should be derated in power by a factor of 2 for safety. 
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> On the low volt side, with 6 Hy you need a 6,000 ohm load, and it works out to 45 mA as well. But the power dissipation is only 12 W.
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> The big question is how the load behaves. If it's a steady load like a Class A amp, you may only need a safety bleeder (high value, just to make cure the C discharges.