Path: Xl.tags.giganews.com!local-1.nntp.ord.giganews.com!nntp.supernews.com!news.supernews.com.POSTED!not-for-mail NNTP-Posting-Date: Sat, 11 May 2024 14:31:15 +0000 From: John Larkin Newsgroups: sci.electronics.design Subject: Re: Another design Date: Sat, 11 May 2024 07:29:26 -0700 Organization: Highland Tech Reply-To: xx@yy.com Message-ID: References: X-Newsreader: Forte Agent 3.1/32.783 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 92 X-Trace: sv3-H8VkQUlYFFb3Zg0IIIn43EPfE7bJOgSKc5yXkt9xnj7Qgh4I8YEYvfrG4xfbvbxqQtt1ge3RRMjM9zP!/j3ELOer3g5IgPLx9AeWExFN3GSlGmw4B6YVwUsShPOlbiXURD5IIzb8SoHs3LS4ezyavIqMzTXl!Bv1UGw== X-Complaints-To: www.supernews.com/docs/abuse.html X-DMCA-Complaints-To: www.supernews.com/docs/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 Bytes: 4367 On Fri, 10 May 2024 18:17:47 -0400, "Edward Rawde" wrote: >"piglet" wrote in message >news:v1m48d$1j1bc$1@dont-email.me... >> Edward Rawde wrote: >>> "John Larkin" wrote in message >>> news:gnps3j99nl7t4dkdt22k7oe5tr0e6dh60i@4ax.com... >>>> On Thu, 9 May 2024 23:11:03 -0400, "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. >>>> >>>> I think the LED constant-current switcher can be done with a pfet and >>>> two NPN transistors. >>>> >>> >>> Ok here's the spec. >>> >>> Input voltage range 10.5V to 12.6 V. Preferably 10V to 15V. >>> >>> Minimum efficiency. 80% >>> >>> Inductor not bigger than 68uH 1A. Preferably smaller. >>> >>> One, two or three LEDs at 500mA +/- 50mA >>> >>> Filtered LED feed referenced to ground. >>> >>> Maximum total LED wiring length. 12 inches. >>> >>> EMC compliant in all countries. >>> >>> Cost. Minimum which will meet spec. >>> >>> >>> >> >> My LM311 based idea works ok with 68uH inductors too. Efficiency is above >> 80% for supply 10 to 13V and still 77% at 16V >> >> Haven't explored 1, 2 or 3 LED outputs. >> >> You didn't say if "ground" was input negative or positive but if positive >> ground then flip the circuit over and use a cheaper N-channel FET :) >> >> The input to a buck converter is pulsed current - you have mentioned >> output >> leads but some, possibly extensive, filtering will be needed on the input. > >That makes me wonder whether the input could be made near enough DC by using >two converters. >One taking current when the other isn't. Perhaps two LEDs each. > >Thanks for all your input. I think I'm just about done with this unless John >Larkin want to show his pfet and one npn circuit. > >> >> Pay me for EMC compliance :) >> >> -- >> piglet > Something like this should work. https://www.dropbox.com/scl/fi/su03d8gaxbi67zhufz3th/LED_CC_Reg_1.jpg?rlkey=oh4ib9011ee1c74ih7hk7dzcb&raw=1 But I'd rather use a TPS562208, which would be cheaper and simpler and has spread-spectrum to help the EMC thing by about 20 dB.