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From: KevinJ93 <kevin_es@whitedigs.com>
Newsgroups: sci.electronics.design
Subject: Re: KA7500 vs TL494
Date: Sun, 6 Apr 2025 09:46:27 -0700
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On 4/6/25 3:29 AM, John R Walliker wrote:
<...>
> All these power supplies are the three-contact barrel type.  They
> all deliver a fixed 19.5V, even into a resistive load.  They can
> also all deliver well over their rated output currents.  The issue
> seems to be that their failure mode is an inability to retry when
> the current limit has been triggered.
> I don't think they have any mechanism for negotiating like a USB-C
> PD supply.  Instead they just have a memory accessed through a 1-wire
> interface which tells the computer what their rating is.
> 
> John
> 

The first time I cam across one of these I accidentally shorted the 
inner ring to the centre pin while measuring the output voltage.

Subjecting the One-wire device to that 19V destroyed it so the computer 
refused to recognize the power supply and would only work at a lower CPU 
speed and not charge the battery.

I disassembled the supply and I was surprized to find there is no 
protection circuitry to prevent this type of damage.

So be careful when measuring the voltage output of these supplies.

kw