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From: piglet <erichpwagner@hotmail.com>
Newsgroups: sci.electronics.design
Subject: Re: Another design
Date: Fri, 10 May 2024 21:26:11 +0100
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On 10/05/2024 7:57 pm, Edward Rawde wrote:
> "piglet" <erichpwagner@hotmail.com> wrote in message
> news:v1li00$1eir3$1@dont-email.me...
>> 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.
>>>
> ...
>>
>>
>> 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%.
>>
> 
> Thanks, that works but I was hoping for a smaller inductor at about 1MHz and
> filtered LED feed referenced to ground for up to three LEDs.
> 
> I'm probably done with my circuit unless there's a cheaper comparator which
> can do the same job or a cheaper op amp which can run on lead acid voltage.
> Or preferably up to 15V.
> Also a cheaper fet.
> 
> 

Ground referenced output is possible, rearrange the sense resistor and 
stand the reference on top of the LEDs. As in ...

Version 4
SHEET 1 996 708
WIRE -544 -112 -704 -112
WIRE -48 -112 -544 -112
WIRE 48 -112 -48 -112
WIRE 192 -112 48 -112
WIRE 336 -112 192 -112
WIRE 48 -96 48 -112
WIRE 192 -48 192 -112
WIRE -544 -16 -544 -112
WIRE 48 0 48 -16
WIRE 128 0 48 0
WIRE 336 64 336 -112
WIRE 192 80 192 48
WIRE 288 80 192 80
WIRE -544 176 -544 64
WIRE -448 176 -544 176
WIRE -240 224 -288 224
WIRE 336 224 336 160
WIRE 336 224 -160 224
WIRE -448 240 -448 176
WIRE 336 272 336 224
WIRE 416 272 336 272
WIRE 528 272 496 272
WIRE 624 272 528 272
WIRE -704 320 -704 -112
WIRE 528 320 528 272
WIRE 528 320 400 320
WIRE 624 320 624 272
WIRE -160 336 -192 336
WIRE -48 336 -48 -112
WIRE -48 336 -80 336
WIRE -544 352 -544 176
WIRE -48 384 -48 336
WIRE 192 384 192 80
WIRE -448 416 -448 320
WIRE -288 416 -288 224
WIRE -288 416 -448 416
WIRE -80 416 -288 416
WIRE 48 432 48 0
WIRE 48 432 0 432
WIRE 128 432 48 432
WIRE -192 448 -192 336
WIRE -80 448 -192 448
WIRE 480 448 432 448
WIRE 624 448 624 400
WIRE 624 448 480 448
WIRE -448 464 -448 416
WIRE 336 464 336 272
WIRE 624 480 624 448
WIRE -192 496 -192 448
WIRE 480 496 480 448
WIRE -544 560 -544 416
WIRE -448 560 -448 544
WIRE -448 560 -544 560
WIRE -704 592 -704 400
WIRE -64 592 -64 480
WIRE -64 592 -704 592
WIRE -48 592 -48 480
WIRE -48 592 -64 592
WIRE 192 592 192 480
WIRE 192 592 -48 592
WIRE 336 592 336 528
WIRE 336 592 192 592
WIRE 480 592 480 560
WIRE 480 592 336 592
WIRE 624 592 624 544
WIRE 624 592 480 592
WIRE -704 640 -704 592
WIRE -192 672 -192 576
WIRE 400 672 400 320
WIRE 400 672 -192 672
WIRE -448 688 -448 560
WIRE 432 688 432 448
WIRE 432 688 -448 688
FLAG -704 640 0
SYMBOL schottky 352 528 R180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D1
SYMATTR Value 1N5817
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL ind 400 288 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 5 56 VBottom 2
SYMATTR InstName L1
SYMATTR Value 0.22m
SYMATTR SpiceLine Rser=50m
SYMBOL LED 608 480 R0
SYMATTR InstName D2
SYMATTR Value LXK2-PW14
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL voltage -704 304 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 12
SYMBOL res 608 304 R0
SYMATTR InstName R8
SYMATTR Value 0.15
SYMBOL zener -528 416 R180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D3
SYMATTR Value 1N750
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL res -560 -32 R0
SYMATTR InstName R1
SYMATTR Value 2k
SYMBOL res -464 448 R0
SYMATTR InstName R3
SYMATTR Value 100
SYMBOL res -464 224 R0
SYMATTR InstName R2
SYMATTR Value 4.3k
SYMBOL res 32 -112 R0
SYMATTR InstName R7
SYMATTR Value 10k
SYMBOL cap 464 496 R0
SYMATTR InstName C1
SYMATTR Value 0.1m
SYMBOL res -144 208 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R4
SYMATTR Value 33k
SYMBOL res -176 592 R180
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