[MRCA] bC-474 Power Supply

[Robert Nickels]

On 6/27/2025 11:55 AM, B. Smith via MRCA wrote:
> what frequency does it operate and what are the intensity of the harmonics

The UC3843 datasheet shows the typical oscillator frequency as 100 kHz 
with a maximum of 500 kHz.   All the "ZVS" modules I've seen are set to 
run at 75 kHz.    Neither fundamental or harmonics are present at the 
output but as I noted,  magnetic coupling can occur.  I verified that by 
using my favorite "direction finder" receiver that tunes the LF and BC 
bands - no noticable difference in the reception of an AM BC signal was 
heard unless I put the loop antenna very close to the power supply, and 
then it was a broadband racket, not a single tone.   Nothing was heard 
on any harmonic either, and a spectrum analyzer showed no peaks with 
.5,  2, and 10 MHz span.

In the time domain, scoping the output does show noise spikes,  
depending on when I captured the waveform I could get just about any 
frequency but I captured the 300V and 12V signals where the scope 
thought the fundamental was the strongest frequency to measure.

Here is the HV output measured via a 100X probe with 300VDC and a 60ma load:


And here's what the 12 input looked like:


Remember these boards only have 10uF of output filtering, which is good 
enough to filter the PWM residue from DC but additional high frequency 
bypassing is a good idea. Good old filtering and shielding...

73, Bob W9RAN

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