Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail From: KevinJ93 Newsgroups: sci.electronics.design Subject: Re: KA7500 vs TL494 Date: Sun, 6 Apr 2025 09:46:27 -0700 Organization: A noiseless patient Spider Lines: 27 Message-ID: References: <2ob3vjlupei56pu5m88hohaa06k91bgppp@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Injection-Date: Sun, 06 Apr 2025 18:46:28 +0200 (CEST) Injection-Info: dont-email.me; posting-host="5ca2cb4a6ab66c4b1c7e17965e49f978"; logging-data="1549901"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1+zmRqk7Xjx1kjnff+tWo1m" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:YNXWQh7s/d6BAyp0VZO6UcIpuwg= Content-Language: en-US In-Reply-To: Bytes: 2268 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