On Mon, 15 Nov 2021 00:22:45 -0500, "Tom Del Rosso"
<fizzbintuesday@that-google-mail-domain.com> wrote:
>jlarkin@highlandsniptechnology.com wrote:
>>
>> Note: an LM317 is not an LDO. A lot of people have taken to using
>> "LDO" for most any linear reg.
>
>But do all LDO's use a PNP or PMOS and the converse?
Most positive ones do.
LM1117 is an "MDO", an npn output transistor with a single Vbe
junction drop from V+ to Vout. Nice part. It will make 3.3 from +5.
There have been some regs that use n-type devices but had an aux
supply voltage for the gate drive. I've designed some like that, with
an opamp and an nfet pass device and dropouts near 0.1 volts. The nfet
becomes ohmic.
--
Father Brown's figure remained quite dark and still;
but in that instant he had lost his head. His head was
always most valuable when he had lost it.
Reply by Tom Del Rosso●November 15, 20212021-11-15
jlarkin@highlandsniptechnology.com wrote:
>
> Note: an LM317 is not an LDO. A lot of people have taken to using
> "LDO" for most any linear reg.
But do all LDO's use a PNP or PMOS and the converse?
--
Defund the Thought Police
Reply by Peter●November 14, 20212021-11-14
Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> wrote
>
>2 * 300 = 600 mA
>USB spec?
>first google hit for 'maximum current from USB':
> "Most computer USB ports supply 5V of electricity with a maximum current of 0.5A.
> This amount of current is standard across the majority of computers
> and means the overall power output will be 2.5 Watts at best.
> Later USB designs bring that current up to 0.9A."
>
>So it all depends..
That isn't an issue. USB can give you only 500mA, unless you implement
the power negotiation protocol which involves connecting resistors to
the two data lines. So a reg which current limits somewhere in the
400mA area is just fine.
Only one regulator is fed from USB.
The other one is fed from the 5V switcher.
Reply by Rick C●November 14, 20212021-11-14
On Sunday, November 14, 2021 at 2:53:24 AM UTC-4, Jan Panteltje wrote:
> On a sunny day (Sat, 13 Nov 2021 21:12:11 +0000) it happened Peter
> <nos...@nospam9876.com> wrote in <smp9n9$te9$2...@dont-email.me>:
>
> >
> >bitrex <us...@example.net> wrote
> >
> >>Just for fun this thing ORs two of the kind that have reverse-current
> >>protection, and then if both inputs are above the undervoltage lockout
> >>it picks whatever regulator has the higher input voltage using a over
> >>the top comparator, and shuts the other down
> >
> >I don't have the software to plot those numbers.
> >
> >FYI my application is one where two 300mA regs are generating 3.3V
> >from one of two sources:
> >
> >a) 5V (poorly regulated) from a switching psu
> >b) 5V from a USB source
> >
> >Both might be present concurrently, which doesn't matter.
>
> 2 * 300 = 600 mA
> USB spec?
> first google hit for 'maximum current from USB':
> "Most computer USB ports supply 5V of electricity with a maximum current of 0.5A.
> This amount of current is standard across the majority of computers
> and means the overall power output will be 2.5 Watts at best.
> Later USB designs bring that current up to 0.9A."
>
> So it all depends..
I think you are making a mistaken assumption the intent is to supply the circuit from both sources at the same time rather than using them independently as a primary and a backup source. From the original post I see...
On 11/11/2021 5:01 PM, Peter wrote:
> Sometimes one needs to power a circuit from one source or another.
He also says...
> >Both might be present concurrently, which doesn't matter.
So there is no current sharing going on. I don't think more than 300 mA is required at the output.
--
Rick C.
- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209
Reply by Jan Panteltje●November 14, 20212021-11-14
On a sunny day (Sat, 13 Nov 2021 21:12:11 +0000) it happened Peter
<nospam@nospam9876.com> wrote in <smp9n9$te9$2@dont-email.me>:
>
>bitrex <user@example.net> wrote
>
>>Just for fun this thing ORs two of the kind that have reverse-current
>>protection, and then if both inputs are above the undervoltage lockout
>>it picks whatever regulator has the higher input voltage using a over
>>the top comparator, and shuts the other down
>
>I don't have the software to plot those numbers.
>
>FYI my application is one where two 300mA regs are generating 3.3V
>from one of two sources:
>
>a) 5V (poorly regulated) from a switching psu
>b) 5V from a USB source
>
>Both might be present concurrently, which doesn't matter.
2 * 300 = 600 mA
USB spec?
first google hit for 'maximum current from USB':
"Most computer USB ports supply 5V of electricity with a maximum current of 0.5A.
This amount of current is standard across the majority of computers
and means the overall power output will be 2.5 Watts at best.
Later USB designs bring that current up to 0.9A."
So it all depends..
Reply by Peter●November 13, 20212021-11-13
bitrex <user@example.net> wrote
>Just for fun this thing ORs two of the kind that have reverse-current
>protection, and then if both inputs are above the undervoltage lockout
>it picks whatever regulator has the higher input voltage using a over
>the top comparator, and shuts the other down
I don't have the software to plot those numbers.
FYI my application is one where two 300mA regs are generating 3.3V
from one of two sources:
a) 5V (poorly regulated) from a switching psu
b) 5V from a USB source
Both might be present concurrently, which doesn't matter.
Reply by bitrex●November 13, 20212021-11-13
On 11/13/2021 7:29 AM, Peter wrote:
>
> bitrex <user@example.net> wrote
>
>> Some LDOs tie the bulk of the FET to ground so they don't conduct in
>> reverse, as so:
>>
>> <https://www.ti.com/product/TPS7A37>
>
> Nice chip but not cheap.
>
> The Ricoh ones are still a good option.
>
Just for fun this thing ORs two of the kind that have reverse-current
protection, and then if both inputs are above the undervoltage lockout
it picks whatever regulator has the higher input voltage using a over
the top comparator, and shuts the other down
Version 4
SHEET 1 1304 1460
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FLAG -336 -64 V1
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SYMBOL PowerProducts\\LT3033 160 160 R0
SYMATTR InstName U1
SYMBOL voltage -448 0 R0
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SYMBOL PowerProducts\\LT3033 96 1072 R0
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TEXT -544 616 Left 2 !.tran 1m startup
Nice chip but not cheap.
The Ricoh ones are still a good option.
Reply by bitrex●November 12, 20212021-11-12
On 11/12/2021 9:24 AM, jlarkin@highlandsniptechnology.com wrote:
> On Fri, 12 Nov 2021 07:07:56 +0000, Peter <nospam@nospam9876.com>
> wrote:
>
>>
>> jlarkin@highlandsniptechnology.com wrote
>>
>>>> One obvious solution is to use a normal LDO and have a diode in series
>>>> with the input, so long as you can be sure nothing funny will be
>>>> hapenning inside with the ground lead which could still pass negative
>>>> current.
>>>
>>> Or put a schottky diode on the output but take the feedback from after
>>> the diode.
>>
>> Sure, but then you are building your own regulator.
>
> No, just using a chip that has a feedback pin. That's common in LDOs.
>
> What regs are you considering?
>
> Note: an LM317 is not an LDO. A lot of people have taken to using
> "LDO" for most any linear reg.
>
Reply by Jan Panteltje●November 12, 20212021-11-12
On a sunny day (Fri, 12 Nov 2021 10:08:39 -0800) it happened John Larkin
<jlarkin@highland_atwork_technology.com> wrote in
<3bbtogh6jstka4039uimng3q8baguk94i3@4ax.com>:
>On Fri, 12 Nov 2021 08:09:35 GMT, Jan Panteltje
><pNaOnStPeAlMtje@yahoo.com> wrote:
>
>>On a sunny day (Thu, 11 Nov 2021 22:01:33 +0000) it happened Peter
>><nospam@nospam9876.com> wrote in <smk3rt$72m$1@dont-email.me>:
>>
>>>Sometimes one needs to power a circuit from one source or another.
>>>
>>>Most LDOs, or indeed most normal regs, feed current back up to the
>>>source. LDOs tend to use a PMOS pass transistor which has a parasitic
>>>diode.
>>>
>>>I am doing a design where I am using the Ricoh R1191 for this
>>>
>>>https://eu.mouser.com/ProductDetail/Ricoh-Electronic-Devices-Company/R1191N033B-TR-FE?qs=%2Fha2pyFaduhEV6ZG3xOqbaXpStP%2FIzlm74
>>>g8
>>>V5lGNcwdefxpMkR8XA%3D%3D
>>>
>>>which has a series diode, so the dropout voltage is about 0.7V.
>>>
>>>It's not dirt cheap but not crazy-priced either.
>>>
>>>I am wondering why this is rare. Is it not possible to make a PMOS
>>>device without the parasitic diode? Or have some other series element
>>>which gets turned off when there is no input? It reminds me of an
>>>active rectifier in switching power supplies, to avoid the Vf of the
>>>diode(s). There is even a circuit for a bridge rectifier, although
>>>that was commercially implemented with a complicated chip to drive the
>>>four gates, IIRC.
>>>
>>>One obvious solution is to use a normal LDO and have a diode in series
>>>with the input, so long as you can be sure nothing funny will be
>>>hapenning inside with the ground lead which could still pass negative
>>>current.
>>
>>IIRC the correct way to parallel 2 voltage regulators is have each one sense its output current
>>and if too high drive the current reference of the other one higher until both deliver the same current.
>>If you just parallel voltage controlled ones then one is likely to do all the work
>>due to minuscule output voltage differences.
>>For example one could go into current limit at 100% current and the other will then do say 10%.
>>Much simpler to get or design one bigger one?
>>
>>
>>
>
>You can certainly diode OR the input of a single reg, from two
>sources.
Of course, but that is different, and even then the highest input will deliver everything,
although having high internal resistance sources / 'feeble' diodes would share ..