Subject: GLOWBUGS digest 61

From: [email-masked]
Date: Sat, 30 Dec 1995 02:03:41 -0600 (CST)

GLOWBUGS Digest 61

Topics covered in this issue include:

  1) Bypassing Silicon Diodes
	by [email-masked]

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Date: Sat, 30 Dec 1995 03:00:36 -0500
From: [email-masked]
To: [email-masked]
Subject: Bypassing Silicon Diodes
Message-ID: <[email-masked]>

Many thanks for the responses to my post regarding hum generated in my quick
and ugly breadboard power supply.  I was going to say quick and dirty but, I
was able to clean it up very nicely.

The first fix was the bypassing of the silicon rectifyers.  I simply placed
0.01 uF caps in parallel with each of the four diodes in the bridge.  Two
explanations were presented as to why this bypassing technique works.  I
believe the primary cause of the hum to be the "hard switching"
characteristic of the diodes.  In this case the power supply was very lightly
loaded and so each diodes would only conduct a small fraction of each half
cycle generating harmonic energy that could eaisly reach 40 and 49 meters.
 In theory the harmonics can be restricted to lower frequencies simply by
forcing the diodes to conduct during a greater portion of the cycle.  An easy
way to verify this theory would be to decrease the bleeder resistor value
but, I am not eager to clip out the caps just to test this theory.  Perhaps
I'll try this when I make the slow and pretty version of the power supply.

I too had read of the problem with RF leaking backwards into the power supply
and mixing with 60/120 Hz.  In my case I think this was a secondary effect as
I was unable to eliminate the hum by placing large ferrite cores on the power
supply leads.

By the way, those ferrite cores are real nifty devices for removing rf from
just about any place it's not suposed to be.  The cores I am using were
removed from discarded video monitor cables I fished out of the trash.  Just
one of these cores was able to restore domestic tranquility in my home by
keeping the CW buzz out of my wife's telephone calls.

73's,  Eric WD6DGX

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End of GLOWBUGS Digest 61
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