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Failed to connect to MySQL: (1203) User howardkn already has more than 'max_user_connections' active connectionsPath: ...!weretis.net!feeder8.news.weretis.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: piglet Newsgroups: sci.electronics.design Subject: Re: DC relay latching voltage Date: Sat, 24 Aug 2024 22:10:49 -0000 (UTC) Organization: A noiseless patient Spider Lines: 35 Message-ID: References: <1qysk8m.2fhd7fnqs3kN%liz@poppyrecords.invalid.invalid> <2b3kcj5afjscdrlcpkjc3jbg0u23ji0kg0@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Injection-Date: Sun, 25 Aug 2024 00:10:50 +0200 (CEST) Injection-Info: dont-email.me; posting-host="8d92ddee19a3c82fdd11cd816e270606"; logging-data="1648342"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1//5TdaqqwRQHsQtlvFfy62" User-Agent: NewsTap/5.5 (iPhone/iPod Touch) Cancel-Lock: sha1:ljcz3bWKCvrLOgrj19eLI4EAciY= sha1:XU3ZxSVLjClJUAIxyz+VCl7iAFI= Bytes: 2501 john larkin wrote: > On Sat, 24 Aug 2024 11:11:19 +0100, liz@poppyrecords.invalid.invalid > (Liz Tuddenham) wrote: > >> Pimpom wrote: >> [...] >>> Normal power supply decay will not release the relay quickly enough. So >>> I've added a section that turns the 12V relay off when the decaying PS >>> drops below 7.5V. Works fine in simulation. >>> >>> However, due to interaction with other sections, the gate voltage of the >>> transistor driving the relay rises again briefly to about 2.5V before >>> the shutdown process is complete. But by this time, the 12V supply has >>> dropped to less than 3V. >> >> Add a few diode drops in the supply to the Base of the transistor and a >> pull-down resistor from Base to Earth. You could even use a 7.5v Zener >> so the transistor switched directly off the PS and no other active >> components were needed. > > A 2-resistor voltage divider can reduce mosfet gate swing. > > Or an R-C in his case of a transient gate drive spike. > > Or both. > > If the C is gate to drain (or base to collector) then the miller effect slows rate of flux collapse enough to remove need for any additional components across the coil. -- piglet