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From: piglet <erichpwagner@hotmail.com>
Newsgroups: sci.electronics.design
Subject: Re: Another design
Date: Fri, 10 May 2024 20:16:56 -0000 (UTC)
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Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
>> piglet <erichpwagner@hotmail.com> wrote:
>>> On 10/05/2024 4:11 am, Edward Rawde 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.
>>>> 
>>>> 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 
> 

Right , I actually did as you described in an earlier version but a PNP is
practically the same cost as a diode and provides added beef.

-- 
piglet