Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Phil Hobbs Newsgroups: sci.electronics.design Subject: Re: Another design Date: Fri, 10 May 2024 17:20:01 -0000 (UTC) Organization: A noiseless patient Spider Lines: 58 Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Injection-Date: Fri, 10 May 2024 19:20:01 +0200 (CEST) Injection-Info: dont-email.me; posting-host="cee801b21fd5f7a720db48ccf1033638"; logging-data="1561989"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1+IrshlD6M2wW+Z6ZvcRZv9" User-Agent: NewsTap/5.5 (iPhone/iPod Touch) Cancel-Lock: sha1:qbRMlb9t6Clr0AHbZh4W9JmfUb4= sha1:C3DjWSREYE2WS7ZSNwvNiTYA4xE= Bytes: 3226 Phil Hobbs wrote: > piglet wrote: >> On 10/05/2024 4:11 am, Edward Rawde wrote: >>> "Edward Rawde" wrote in message >>> news:v1ho21$4ps$1@nnrp.usenet.blueworldhosting.com... >>>> Now with 9V to 15V input range, direct gate drive and 500mA LED current. >>>> >>>> Startup behaviour is not ideal but maybe that can be fixed if it needs >>>> fixing. >>>> >>>> What's the cheapest op amp I can use for U2 instead of OP07? >>>> >>>> Is there a cheaper comparator instead of LT1719 which will work? >>>> Also the fet is bigger than it needs to ne. >>>> >>>> Is there a better device for D4? Particularly if R4 can be reduced. >>>> >>>> Will it work at all? Except in simulation. >>>> >>> >>> I think I've answered my own question for the current controller but I don't >>> think it's feasible to attempt a discrete comparator on cost grounds. >>> >>> Version 4 > (Sniiip) >> >> >> The venerable LM311 is still a good value comparator, if you want to >> penny pinch omit the gate driver buffers and lower the pullup resistor >> but efficiency will drop a lot from 85% to ca 72%. >> >> >> >> >> > I’m not following through all the spicery, but fwiw: > The positive drive of an LM311 can be improved by 100x or more, by adding a > 2-cent NPN and a 2-cent diode. The NPN is an emitter follower, and the > diode goes from base to emitter, reverse biases when the NPN is on. > > It pulls down to a diode drop above ground, but that can be a Schottky, and > only has to handle the base bias, so it can be below 0.2 V, but you don’t > care about 0.7 V in a gate driver anyway. > > When the 311 goes low, the diode doesn’t start conducting till the > transistor is off, and there’s no stored charge to worry about, since the > NPN never saturates. > Oh, and take the output from the emitter. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics