Re: KA7500 vs TL494

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