Reply by November 15, 20212021-11-15
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 WIRE -336 0 -336 -64 WIRE -336 0 -448 0 WIRE -96 0 -336 0 WIRE 32 0 -96 0 WIRE 448 0 288 0 WIRE 592 0 448 0 WIRE 800 0 592 0 WIRE 1040 0 800 0 WIRE 1200 0 1040 0 WIRE -448 16 -448 0 WIRE -96 16 -96 0 WIRE 448 16 448 0 WIRE -336 96 -336 0 WIRE -448 112 -448 96 WIRE -96 112 -96 96 WIRE 32 112 -96 112 WIRE 448 112 448 96 WIRE 448 112 288 112 WIRE 448 128 448 112 WIRE 592 176 592 0 WIRE 1040 176 1040 0 WIRE -336 224 -336 176 WIRE -192 224 -336 224 WIRE 32 224 -192 224 WIRE 448 224 448 208 WIRE 32 336 0 336 WIRE 416 336 288 336 WIRE 512 336 496 336 WIRE -192 400 -192 224 WIRE 160 416 160 384 WIRE 800 432 800 0 WIRE 848 448 816 448 WIRE -96 464 -96 112 WIRE 752 464 -96 464 WIRE 848 480 816 480 WIRE 768 528 768 496 WIRE 800 528 800 496 WIRE 1040 528 1040 256 WIRE 1040 528 800 528 WIRE 1136 528 1040 528 WIRE 1040 576 1040 528 WIRE 1040 576 832 576 WIRE -192 624 -192 464 WIRE 592 624 592 256 WIRE 592 624 -192 624 WIRE 656 624 592 624 WIRE 768 624 736 624 WIRE -192 752 -192 624 WIRE 832 752 832 672 WIRE 1136 832 1136 528 WIRE 1136 832 832 832 WIRE -336 912 -336 848 WIRE -336 912 -448 912 WIRE -112 912 -336 912 WIRE -32 912 -112 912 WIRE 384 912 224 912 WIRE 624 912 384 912 WIRE 944 912 624 912 WIRE 1200 912 1200 0 WIRE 1200 912 944 912 WIRE -448 928 -448 912 WIRE -112 928 -112 912 WIRE 384 928 384 912 WIRE -336 1008 -336 912 WIRE -448 1024 -448 1008 WIRE -112 1024 -112 1008 WIRE -32 1024 -112 1024 WIRE 384 1024 384 1008 WIRE 384 1024 224 1024 WIRE 384 1040 384 1024 WIRE 1200 1072 1200 912 WIRE 944 1104 944 912 WIRE -336 1136 -336 1088 WIRE -192 1136 -192 816 WIRE -192 1136 -336 1136 WIRE -32 1136 -192 1136 WIRE 384 1136 384 1120 WIRE -32 1248 -64 1248 WIRE 352 1248 224 1248 WIRE 448 1248 432 1248 WIRE 944 1280 944 1168 WIRE 1200 1280 1200 1152 WIRE 96 1312 96 1296 WIRE 624 1344 624 912 WIRE 672 1360 640 1360 WIRE -112 1376 -112 1024 WIRE 576 1376 -112 1376 WIRE 672 1392 640 1392 WIRE 592 1440 592 1408 WIRE 624 1440 624 1408 WIRE 832 1440 832 832 WIRE 832 1440 624 1440 FLAG -448 112 0 FLAG 160 416 0 FLAG 512 336 0 FLAG 448 224 0 FLAG 0 336 0 FLAG -448 1024 0 FLAG 96 1312 0 FLAG 448 1248 0 FLAG 384 1136 0 FLAG 1200 1280 0 FLAG 944 1280 0 FLAG -64 1248 0 FLAG 768 528 0 FLAG 832 752 0 FLAG 592 1440 0 FLAG -336 -64 V1 FLAG -336 848 V2 FLAG 848 448 V2 FLAG 848 480 V1 FLAG 672 1360 V1 FLAG 672 1392 V2 SYMBOL PowerProducts\\LT3033 160 160 R0 SYMATTR InstName U1 SYMBOL voltage -448 0 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 2.7 SYMBOL res 432 0 R0 SYMATTR InstName R1 SYMATTR Value 60.4k SYMBOL res 432 112 R0 SYMATTR InstName R2 SYMATTR Value 3.92k SYMBOL res 512 320 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 442 SYMBOL res -352 80 R0 SYMATTR InstName R4 SYMATTR Value 10k SYMBOL PowerProducts\\LT3033 96 1072 R0 SYMATTR InstName U2 SYMBOL voltage -448 912 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value 3.8 SYMBOL res 368 912 R0 SYMATTR InstName R5 SYMATTR Value 60.4k SYMBOL res 368 1024 R0 SYMATTR InstName R6 SYMATTR Value 3.92k SYMBOL res 448 1232 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R7 SYMATTR Value 442 SYMBOL res -352 992 R0 SYMATTR InstName R8 SYMATTR Value 10k SYMBOL res 1184 1056 R0 SYMATTR InstName Rload1 SYMATTR Value 100 SYMBOL cap 928 1104 R0 SYMATTR InstName C2 SYMATTR Value 47&micro; SYMBOL OpAmps\\ADA4098-1 784 464 M0 SYMATTR InstName U3 SYMBOL diode -176 464 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D1 SYMATTR Value 1N4148 SYMBOL diode -208 752 R0 SYMATTR InstName D2 SYMATTR Value 1N4148 SYMBOL res 576 160 R0 SYMATTR InstName R9 SYMATTR Value 470k SYMBOL npn 768 576 R0 SYMATTR InstName Q1 SYMATTR Value 2N3904 SYMBOL res 1024 160 R0 SYMATTR InstName R10 SYMATTR Value 10k SYMBOL res 752 608 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R11 SYMATTR Value 100k SYMBOL OpAmps\\ADA4098-1 608 1376 M0 SYMATTR InstName U4 SYMBOL res -112 0 R0 SYMATTR InstName R12 SYMATTR Value 10k SYMBOL res -128 912 R0 SYMATTR InstName R13 SYMATTR Value 10k TEXT -544 616 Left 2 !.tran 1m startup
Reply by Peter November 13, 20212021-11-13
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.
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. >
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>
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 ..