[ARC5] Troubleshooting Tips from the Late Nick Broline, #2

[kn7sfz]

David, I see Nick had only recently moved to a wonderful spread in Tulsa 
and was planning a bright future according to his qrz.com bio.

How old was he when he passed and the cause?

Thanks,

Richard kn7sfz



On 7/9/2023 10:25 AM, David Stinson wrote:
> Back in 2021, Nick and I were experimenting with
> those little yellow "0-400VDC" power supplies you
> see on Amazon and Ebay.
> There has been some recent discussion concerning them,
> so those with an interest might find Nick's preliminary
> tests interesting.
> ----------------------------------
>
> I had ordered 4 of the yellow colored 45-395V boost converters a year 
> ago, then promptly misplaced them. Took three days to find!
> (Lord, I know that feeling. DS)
>
> I put the supply feeding a 20W wire-wound w 3.5K load. Ran it off a 
> 13.5 VDC fixed output enclosed Lambda enclosed supply.
>
> That looks like the following:
>
> @180V Io = 51ma. W = 9.25W
>
> @220V Io = 63ma W = 13.8W
>
> @250V Io = 71 ma W = 17.9W
>
> What I found was that the 180V performance was bulletproof into the R 
> load. It the switcher could start with that resistive load, and was 
> happy connecting the load and re-applying it while running. This would 
> be perfect for an ARC-5 or ARC-12 receiver under all circumstances.
> The 220 output was about the same.
>
> The 250V output handled the load well, but when I tried to start the 
> supply from the 12V source and the switcher loaded it would ramp up to 
> ~180V and stop. Disconnecting the load, then reapplying it, would let 
> the supply recover to 250V output. This told me the supply would run a 
> receiver well, but it you interrupted the source with the filament hot 
> (and operating on 12V), the supply wouldn't come up all the way.
> Switching to a higher input voltage, like 24V, seemed to work perfectly.
>
> The switcher IC is a TI UC3843A which is a controller that charges an 
> inductor until the current reaches a value specified by the voltage 
> sense circuit. It make a current measurement every cycle. What I'm 
> thinking is that when starting under load the chip runs into its 
> current limit on each cycle and can't deliver any more energy into the 
> inductor (and load, of course), and the control loop can't coax any 
> more output. Looks like the converter gets "stuck." I don't know if 
> anything is getting hot in the supply.
>
> I suppose this says if I want to use the converter at a higher output 
> voltage and current, but still within its limits, it has to be with a 
> higher source voltage to get it to start under load, or needs to 
> always start working into a low current load.
>
> Next time I get back to the bench I'm going to look at the converter 
> with a scope and see if its bumping into another "chip" limitation.
>
> I also noted that the output of the supply overshoots when the 71ma 
> load is removed, and I think that's because they are using a very 
> large output cap (100 ufd, I think) for the application. I seem to 
> recall the normal output cap is a large ceramic, like maybe 
> 2uFd.??????  memory again.....but its been ~25 years since i dealt 
> with these things.
>
> 73
> Nick Broline
>
>
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