Forums

79L05 stability, output capacitance

Started by Joerg January 4, 2016
Folks,

Normally I never use them but today I need a couple of small negative 
regulators, one of them with an upfront 3-4V zener to burn off some 
power outside its package. LM79L05 in SOT89. Older datasheets prescribe 
tantalums (not going to happen here) and newer ones don't mention 
anything other than "0.1uF" or they mention simply nothing. I want to 
use ceramci caps and the grand total of bypass caps is going to be a few uF.

Are those things internally compensated well enough or do they suffer 
the usual LDO ailments of instability at low ESR? Any formal docs on that?

-- 
Regards, Joerg

http://www.analogconsultants.com/
On Mon, 04 Jan 2016 13:43:07 -0800, Joerg <news@analogconsultants.com>
wrote:

>Folks, > >Normally I never use them but today I need a couple of small negative >regulators, one of them with an upfront 3-4V zener to burn off some >power outside its package. LM79L05 in SOT89. Older datasheets prescribe >tantalums (not going to happen here) and newer ones don't mention >anything other than "0.1uF" or they mention simply nothing. I want to >use ceramci caps and the grand total of bypass caps is going to be a few uF. > >Are those things internally compensated well enough or do they suffer >the usual LDO ailments of instability at low ESR? Any formal docs on that?
It's not an LDO in the usual sense, _but_ it is a hokey PNP equivalent pass device made up of a lateral PNP plus an NPN, so it's potentially squirrelly. Disclaimer: I haven't used one in probably 25+ years ;-) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On 2016-01-04 13:59, Jim Thompson wrote:
> On Mon, 04 Jan 2016 13:43:07 -0800, Joerg <news@analogconsultants.com> > wrote: > >> Folks, >> >> Normally I never use them but today I need a couple of small negative >> regulators, one of them with an upfront 3-4V zener to burn off some >> power outside its package. LM79L05 in SOT89. Older datasheets prescribe >> tantalums (not going to happen here) and newer ones don't mention >> anything other than "0.1uF" or they mention simply nothing. I want to >> use ceramci caps and the grand total of bypass caps is going to be a few uF. >> >> Are those things internally compensated well enough or do they suffer >> the usual LDO ailments of instability at low ESR? Any formal docs on that? > > It's not an LDO in the usual sense, _but_ it is a hokey PNP equivalent > pass device made up of a lateral PNP plus an NPN, so it's potentially > squirrelly.
I wonder what it'll say to a big fat ceramic cap on its output.
> ... Disclaimer: I haven't used one in probably 25+ years ;-) >
I raise you another 25 years :-) Can't remember ever having used them on any of my designs. Back in my school days such regulators were unaffordable anyhow. I did almost everything with uA723 or home-brew switchers where the controller was a cheap logic chip. -- Regards, Joerg http://www.analogconsultants.com/
Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com>
 Wrote in message:
> On Mon, 04 Jan 2016 13:43:07 -0800, Joerg <news@analogconsultants.com> > wrote: > >>Folks, >> >>Normally I never use them but today I need a couple of small negative >>regulators, one of them with an upfront 3-4V zener to burn off some >>power outside its package. LM79L05 in SOT89. Older datasheets prescribe >>tantalums (not going to happen here) and newer ones don't mention >>anything other than "0.1uF" or they mention simply nothing. I want to >>use ceramci caps and the grand total of bypass caps is going to be a few uF. >> >>Are those things internally compensated well enough or do they suffer >>the usual LDO ailments of instability at low ESR? Any formal docs on that? > > It's not an LDO in the usual sense, _but_ it is a hokey PNP equivalent > pass device made up of a lateral PNP plus an NPN, so it's potentially > squirrelly. Disclaimer: I haven't used one in probably 25+ years ;-) > > ...Jim Thompson > --
Can they still not make a monolithic PNP power tranny? -- ----Android NewsGroup Reader---- http://usenet.sinaapp.com/
Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com>
 Wrote in message:
> On Mon, 04 Jan 2016 13:43:07 -0800, Joerg <news@analogconsultants.com> > wrote: > >>Folks, >> >>Normally I never use them but today I need a couple of small negative >>regulators, one of them with an upfront 3-4V zener to burn off some >>power outside its package. LM79L05 in SOT89. Older datasheets prescribe >>tantalums (not going to happen here) and newer ones don't mention >>anything other than "0.1uF" or they mention simply nothing. I want to >>use ceramci caps and the grand total of bypass caps is going to be a few uF. >> >>Are those things internally compensated well enough or do they suffer >>the usual LDO ailments of instability at low ESR? Any formal docs on that? > > It's not an LDO in the usual sense, _but_ it is a hokey PNP equivalent > pass device made up of a lateral PNP plus an NPN, so it's potentially > squirrelly. Disclaimer: I haven't used one in probably 25+ years ;-) > > ...Jim Thompson > --
Wasn't there a time when it was PNP discrete transistors that were cheap and readily available, but ICs could only have NPNs? Must have been a pain in the ass era to design power supplies. -- ----Android NewsGroup Reader---- http://usenet.sinaapp.com/
On Mon, 4 Jan 2016 17:44:23 -0500 (EST), bitrex
<bitrex@de.lete.earthlink.net> wrote:

>Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> > Wrote in message: >> On Mon, 04 Jan 2016 13:43:07 -0800, Joerg <news@analogconsultants.com> >> wrote: >> >>>Folks, >>> >>>Normally I never use them but today I need a couple of small negative >>>regulators, one of them with an upfront 3-4V zener to burn off some >>>power outside its package. LM79L05 in SOT89. Older datasheets prescribe >>>tantalums (not going to happen here) and newer ones don't mention >>>anything other than "0.1uF" or they mention simply nothing. I want to >>>use ceramci caps and the grand total of bypass caps is going to be a few uF. >>> >>>Are those things internally compensated well enough or do they suffer >>>the usual LDO ailments of instability at low ESR? Any formal docs on that? >> >> It's not an LDO in the usual sense, _but_ it is a hokey PNP equivalent >> pass device made up of a lateral PNP plus an NPN, so it's potentially >> squirrelly. Disclaimer: I haven't used one in probably 25+ years ;-) >> >> ...Jim Thompson >> -- > >Can they still not make a monolithic PNP power tranny?
X-Fab and IBM have processes with real, high-fT PNP's, but they're expensive multi-layer processes. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On Mon, 4 Jan 2016 17:47:50 -0500 (EST), bitrex
<bitrex@de.lete.earthlink.net> wrote:

>Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> > Wrote in message: >> On Mon, 04 Jan 2016 13:43:07 -0800, Joerg <news@analogconsultants.com> >> wrote: >> >>>Folks, >>> >>>Normally I never use them but today I need a couple of small negative >>>regulators, one of them with an upfront 3-4V zener to burn off some >>>power outside its package. LM79L05 in SOT89. Older datasheets prescribe >>>tantalums (not going to happen here) and newer ones don't mention >>>anything other than "0.1uF" or they mention simply nothing. I want to >>>use ceramci caps and the grand total of bypass caps is going to be a few uF. >>> >>>Are those things internally compensated well enough or do they suffer >>>the usual LDO ailments of instability at low ESR? Any formal docs on that? >> >> It's not an LDO in the usual sense, _but_ it is a hokey PNP equivalent >> pass device made up of a lateral PNP plus an NPN, so it's potentially >> squirrelly. Disclaimer: I haven't used one in probably 25+ years ;-) >> >> ...Jim Thompson >> -- > >Wasn't there a time when it was PNP discrete transistors that were > cheap and readily available, but ICs could only have > NPNs? > >Must have been a pain in the ass era to design power supplies.
I had lateral PNP's available to me (personally) at Motorola in 1962. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com>
 Wrote in message:
> On Mon, 4 Jan 2016 17:47:50 -0500 (EST), bitrex > <bitrex@de.lete.earthlink.net> wrote: > >>Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> >> Wrote in message: >>> On Mon, 04 Jan 2016 13:43:07 -0800, Joerg <news@analogconsultants.com> >>> wrote: >>> >>>>Folks, >>>> >>>>Normally I never use them but today I need a couple of small negative >>>>regulators, one of them with an upfront 3-4V zener to burn off some >>>>power outside its package. LM79L05 in SOT89. Older datasheets prescribe >>>>tantalums (not going to happen here) and newer ones don't mention >>>>anything other than "0.1uF" or they mention simply nothing. I want to >>>>use ceramci caps and the grand total of bypass caps is going to be a few uF. >>>> >>>>Are those things internally compensated well enough or do they suffer >>>>the usual LDO ailments of instability at low ESR? Any formal docs on that? >>> >>> It's not an LDO in the usual sense, _but_ it is a hokey PNP equivalent >>> pass device made up of a lateral PNP plus an NPN, so it's potentially >>> squirrelly. Disclaimer: I haven't used one in probably 25+ years ;-) >>> >>> ...Jim Thompson >>> -- >> >>Wasn't there a time when it was PNP discrete transistors that were >> cheap and readily available, but ICs could only have >> NPNs? >> >>Must have been a pain in the ass era to design power supplies. > > I had lateral PNP's available to me (personally) at Motorola in 1962. > > ...Jim Thompson > --
Some of the decisions I see in power supply design from Japanese equipment I've repaired from the 1980s don't make a lot of sense to me, at least from a modern perspective. Lots of discrete parts, zeners, pass transistors, etc. It's like the were looking at a circuit book from the late 1960s, but this was Japan circa 1986. I'm like, couldn't you guys have just slapped a 7815 in there and called it a day? They couldn't have cost that much even then... -- ----Android NewsGroup Reader---- http://usenet.sinaapp.com/
Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com>
 Wrote in message:
> On Mon, 4 Jan 2016 17:47:50 -0500 (EST), bitrex > <bitrex@de.lete.earthlink.net> wrote: > >>Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> >> Wrote in message: >>> On Mon, 04 Jan 2016 13:43:07 -0800, Joerg <news@analogconsultants.com> >>> wrote: >>> >>>>Folks, >>>> >>>>Normally I never use them but today I need a couple of small negative >>>>regulators, one of them with an upfront 3-4V zener to burn off some >>>>power outside its package. LM79L05 in SOT89. Older datasheets prescribe >>>>tantalums (not going to happen here) and newer ones don't mention >>>>anything other than "0.1uF" or they mention simply nothing. I want to >>>>use ceramci caps and the grand total of bypass caps is going to be a few uF. >>>> >>>>Are those things internally compensated well enough or do they suffer >>>>the usual LDO ailments of instability at low ESR? Any formal docs on that? >>> >>> It's not an LDO in the usual sense, _but_ it is a hokey PNP equivalent >>> pass device made up of a lateral PNP plus an NPN, so it's potentially >>> squirrelly. Disclaimer: I haven't used one in probably 25+ years ;-) >>> >>> ...Jim Thompson >>> -- >> >>Wasn't there a time when it was PNP discrete transistors that were >> cheap and readily available, but ICs could only have >> NPNs? >> >>Must have been a pain in the ass era to design power supplies. > > I had lateral PNP's available to me (personally) at Motorola in 1962. > > ...Jim Thompson >
But you graduated college in 1962. You mean there was a time when people actually got jobs doing what they were trained to do with their degree, right out of school? What halcyon days... -- ----Android NewsGroup Reader---- http://usenet.sinaapp.com/
On Mon, 4 Jan 2016 18:08:25 -0500 (EST), bitrex
<bitrex@de.lete.earthlink.net> wrote:

>Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> > Wrote in message: >> On Mon, 4 Jan 2016 17:47:50 -0500 (EST), bitrex >> <bitrex@de.lete.earthlink.net> wrote: >> >>>Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> >>> Wrote in message: >>>> On Mon, 04 Jan 2016 13:43:07 -0800, Joerg <news@analogconsultants.com> >>>> wrote: >>>> >>>>>Folks, >>>>> >>>>>Normally I never use them but today I need a couple of small negative >>>>>regulators, one of them with an upfront 3-4V zener to burn off some >>>>>power outside its package. LM79L05 in SOT89. Older datasheets prescribe >>>>>tantalums (not going to happen here) and newer ones don't mention >>>>>anything other than "0.1uF" or they mention simply nothing. I want to >>>>>use ceramci caps and the grand total of bypass caps is going to be a few uF. >>>>> >>>>>Are those things internally compensated well enough or do they suffer >>>>>the usual LDO ailments of instability at low ESR? Any formal docs on that? >>>> >>>> It's not an LDO in the usual sense, _but_ it is a hokey PNP equivalent >>>> pass device made up of a lateral PNP plus an NPN, so it's potentially >>>> squirrelly. Disclaimer: I haven't used one in probably 25+ years ;-) >>>> >>>> ...Jim Thompson >>>> -- >>> >>>Wasn't there a time when it was PNP discrete transistors that were >>> cheap and readily available, but ICs could only have >>> NPNs? >>> >>>Must have been a pain in the ass era to design power supplies. >> >> I had lateral PNP's available to me (personally) at Motorola in 1962. >> >> ...Jim Thompson >> > >But you graduated college in 1962. You mean there was a time when > people actually got jobs doing what they were trained to do with > their degree, right out of school? > >What halcyon days...
Actually Motorola offered the job in February 1962, but I didn't graduate from MIT until June. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.