[MRCA] bC-474 Power Supply

[B. Smith]

Its nice to see some actual testing of a device, nothing like a little 
data to help with a decision. Tip of the hat to you Bob. Q. Bob what are 
you using to measure the Heat Sink temperature?
Z



On 6/26/2025 9:00 PM, Robert Nickels wrote:
>
> Data is always good.  I used my Clarostat 240C power decade box to 
> vary the load from 10ma to the point where regulation was lost.   
> Input voltage was 13.0VDC and the resulting current was verified with 
> a Keithley 2000 DMM.
>
> Short version:   After adjusting the output to 300VDC  the output 
> voltage remained between 291 and 298V from 10 ma to 110 ma loads,  
> which translates to a range of 3 to 33 watts into the load.   At 100ma 
> the heatsink temperature was 40C and the input current was 2.56A for 
> input power of 33.28 watts.   Output voltage at 100ma was 292VDC or 
> 29.2 watts, resulting in efficiency of 29.2/33.28 = 88%.    Well 
> within the expected range and in my view, this is the maximum working 
> limit.
>
> At 120ma load current the output was down to 280VDC for 33.6 watts 
> output but the input current was 3.54A or 46 watts,  resulting in 
> efficiency of only 73%.  This was reflected in a rise in the heatsink 
> temperature to 54C. Subjectively, it also "smelled hot".
>
> I've had failures running these things at higher voltages so 300V and 
> 100ma are my practical limits, but that's a substantial amount of 
> regulated HV power!   The output is clean but if you find the need for 
> more, normal filtering and shielding practices apply.  The worst 
> problem I had was in powering a light aircraft receiver with a 75kHz 
> IF - which is right at the switching frequency!   That required 
> shielding and physical separation to eliminate magnetic coupling.    A 
> light load of a few ma helps with regulation at low current and you 
> really want a bleeder resistor anyhow (these things can bite!).
>
> A final tip - make sure any RF loads are well bypassed - it doesn't 
> take much RF getting back into the board to pop the IC.   I keep 
> UC3843s and FETs on hand for those occasions.
>
> 73, Bob W9RAN
>
>
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