From: "Edward Rawde" <invalid@invalid.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Another design
Date: Fri, 10 May 2024 18:05:10 -0400
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"piglet" <erichpwagner@hotmail.com> wrote in message 
news:v1m48d$1j1bc$1@dont-email.me...
> Edward Rawde <invalid@invalid.invalid> wrote:
>> "John Larkin" <jjSNIPlarkin@highNONOlandtechnology.com> wrote in message
>> news:gnps3j99nl7t4dkdt22k7oe5tr0e6dh60i@4ax.com...
>>> On Thu, 9 May 2024 23:11:03 -0400, "Edward Rawde"
>>> <invalid@invalid.invalid> wrote:
>>>
>>>> "Edward Rawde" <invalid@invalid.invalid> 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 :)

Ground is input negative.

>
> 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.

Yes it crossed my mind that the input may need EMC filtering too.

>
> Pay me for EMC compliance :)

As long as it doesn't go in circles with filter this, failed again, filter 
that, failed again, change the layout, failed again, etc

>
> -- 
> piglet