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From: piglet <erichpwagner@hotmail.com>
Newsgroups: sci.electronics.design
Subject: Re: Another design
Date: Sat, 11 May 2024 18:27:33 +0100
Organization: A noisesome patent Spinner
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On 11/05/2024 5:42 pm, John Larkin wrote:
> On Sat, 11 May 2024 16:04:15 +0100, piglet <erichpwagner@hotmail.com>
> wrote:
> 
>> On 11/05/2024 3:29 pm, John Larkin wrote:
>>> On Fri, 10 May 2024 18:17:47 -0400, "Edward Rawde"
>>> <invalid@invalid.invalid> wrote:
>>>
>>>> "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 :)
>>>>>
>>>>> 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.
>>>
>>>
>>
>> Yes, my take is not too far distant but I tried to accomodate the OP's
>> unexplained desire for ground referenced LED output.
> 
> That's nice. It's only an LED, so it probably doesn't need +12v
> compensation.
> 
> LEDs lose light as temperature rises, so it probably doesn't need Vbe
> temp compensation either. I'm glad that you saw the hysteresis trick,
> and that you drew a decent looking schematic with a title, date, and
> author.
> 
> We have one project here that has had three or four project engineers
> so far, and the project folder contains 175 (yes, 175!) .asc files,
> most of which are hideous uncommented messes.
> 
> My sim will be # 176.
> 
> https://www.dropbox.com/scl/fi/i1rmnne2j2f2nhetfg1dn/P941C_May11.jpg?rlkey=9by4bmkzo6iim763468y21ko2&raw=1
> 
> It's a dual isolated programmable DC power supply, but it has remote
> sense and a paralleling relay, which complicate life. We don't know
> what bizarre loads the user will have, or if they will connect the
> remote sense right.
> 
> Sims run super slow and there are many cases to test, so we set up
> three monster PCs in the conference room as a simulator farm, to
> supplement the two we will use in engineers offices.
> 
> 

Thanks.

Compensating feedback systems to cope with wide ranging capacitive loads 
is awkward. I have good results with Phil Perkins stacked RC 3dB/octave 
method.

piglet