TL494

"legg" <legg@nospam.magma.ca> wrote in message 
news:mbrarcpttaupenukgplsccjsnkknrdolga@4ax.com...
> This lack of cyclic latching can complicate any externally-developed
> protection function that is expected to operate on a cycle-by-cycle
> basis. In order to do so, this protection signal must be maintained
> externally, for the full clock cycle.

The appnotes show a solution or two, for implementing peak current mode 
control.  It's a hack at best -- not so much testament to the versatility of 
the part, as it is "if all you have is a hammer" syndrome.

I mean, it doesn't take many more 555s to do the same job, either. :)

Also, one of the app note implementations is blatantly wrong.  But what do 
you expect, the intern probably didn't breadboard, let alone SPICE, the 
thing.

Tim

-- 
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com 

On Mon, 11 Sep 2017 22:13:18 -0500, "Tim Williams"
<tmoranwms@gmail.com> wrote:

>"legg" <legg@nospam.magma.ca> wrote in message 
>news:mbrarcpttaupenukgplsccjsnkknrdolga@4ax.com...
>> This lack of cyclic latching can complicate any externally-developed
>> protection function that is expected to operate on a cycle-by-cycle
>> basis. In order to do so, this protection signal must be maintained
>> externally, for the full clock cycle.
>
>The appnotes show a solution or two, for implementing peak current mode 
>control.  It's a hack at best -- not so much testament to the versatility of 
>the part, as it is "if all you have is a hammer" syndrome.
>
>I mean, it doesn't take many more 555s to do the same job, either. :)
>
>Also, one of the app note implementations is blatantly wrong.  But what do 
>you expect, the intern probably didn't breadboard, let alone SPICE, the 
>thing.
>
>Tim

As the part type has been in the field for 40+ years, you'd have to
give a reference to the app note you're talking about. Most issues
relevant to the era are addressed by the mfr using solutions that made
sense for the applications of that time. 

The original mfr's app notes pre-date any electronic format (or the
non-academic dissemination of Spice modeling) and may have suffered in
the conversion process. Though they are unlikely to have been written
by an 'intern' (author's names and sources are typically preserved),
the usual precautions for typos in anything passing through the sales
department are required.

Industry and consumer print articles employing the part may come from
just about anywhere and demonstrate a wide range of competence and
accuracy. Differing versions of 'improved' part have also been
released by both the original mfr and secondary sources, over the
years, but these usually have significant part numbering differences
and should be investigated independently.

RL

"legg" <legg@nospam.magma.ca> wrote in message 
news:951grchn8d9nmn23562cc1g3tq02rgco01@4ax.com...
> As the part type has been in the field for 40+ years, you'd have to
> give a reference to the app note you're talking about. Most issues
> relevant to the era are addressed by the mfr using solutions that made
> sense for the applications of that time.
>
> The original mfr's app notes pre-date any electronic format (or the
> non-academic dissemination of Spice modeling) and may have suffered in
> the conversion process.

On the contrary; TI's recently updated their TL494 datasheet, in fact! 
(They also added a layout section to the LM555 datasheet.  Go figure?)

They've been updating a lot of their resources, it seems!

Anyway, as we're talking TLxxx, I'm mainly referring to TI's appnotes.  But 
there are others, yes (and other errors :) ).


> Though they are unlikely to have been written
> by an 'intern' (author's names and sources are typically preserved),
> the usual precautions for typos in anything passing through the sales
> department are required.

There are relatively few appnotes with authors on them, actually.  At least 
that I've seen.  LT seems to be a standout in that regard (indeed, their 
appnotes even have character, from time to time, especially the Jim Williams 
ones).  TI not so much.

Pretty sure I've never seen an appnote that shows the author's name AND 
title / qualifications (not that you couldn't look them up separately, of 
course).

And, yeah, I honestly doubt most appnotes are written by interns, but it's a 
lie I tell myself to make myself feel better, that a real engineer couldn't 
be so ignorant as to write such things.

Tim

-- 
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com 

On Tue, 12 Sep 2017 12:47:12 -0500, "Tim Williams"
<tmoranwms@gmail.com> wrote:

>"legg" <legg@nospam.magma.ca> wrote in message 
>news:951grchn8d9nmn23562cc1g3tq02rgco01@4ax.com...
>> As the part type has been in the field for 40+ years, you'd have to
>> give a reference to the app note you're talking about. Most issues
>> relevant to the era are addressed by the mfr using solutions that made
>> sense for the applications of that time.
>>
>> The original mfr's app notes pre-date any electronic format (or the
>> non-academic dissemination of Spice modeling) and may have suffered in
>> the conversion process.
>
>On the contrary; TI's recently updated their TL494 datasheet, in fact! 
>(They also added a layout section to the LM555 datasheet.  Go figure?)
>
>They've been updating a lot of their resources, it seems!
>
>Anyway, as we're talking TLxxx, I'm mainly referring to TI's appnotes.  But 
>there are others, yes (and other errors :) ).
>
>
>> Though they are unlikely to have been written
>> by an 'intern' (author's names and sources are typically preserved),
>> the usual precautions for typos in anything passing through the sales
>> department are required.
>
>There are relatively few appnotes with authors on them, actually.  At least 
>that I've seen.  LT seems to be a standout in that regard (indeed, their 
>appnotes even have character, from time to time, especially the Jim Williams 
>ones).  TI not so much.
>
>Pretty sure I've never seen an appnote that shows the author's name AND 
>title / qualifications (not that you couldn't look them up separately, of 
>course).
>
>And, yeah, I honestly doubt most appnotes are written by interns, but it's a 
>lie I tell myself to make myself feel better, that a real engineer couldn't 
>be so ignorant as to write such things.
>
>Tim

I'm still interested in what was 'just wrong'.

The earliest TL494 app note that was digitized at TI as SLV001 in 1998
dates from 1989 print media, but it originated as Bulletin CA-198 by
John Spencer published in 1978. The external latch is shown as fig27.

The 1998 digitization for SLV001 was image-only, so there was little
chance of 'extra' typographical issues being generated. This was fully
re-edited for later revs to be text-searchable and was still basically
the same information, at revD, in 2005.

Double-pulse suppression was claimed in the part's print data sheet as
early as 1983, but an effective latch is not present in the functional
block diagram of the TL494's (SLVS074) specification sheet, to this
day.

RL

On Tue, 12 Sep 2017 15:28:09 -0400, legg <legg@nospam.magma.ca> wrote:

>On Tue, 12 Sep 2017 12:47:12 -0500, "Tim Williams"
><tmoranwms@gmail.com> wrote:
>
>>"legg" <legg@nospam.magma.ca> wrote in message 
>>news:951grchn8d9nmn23562cc1g3tq02rgco01@4ax.com...
>>> As the part type has been in the field for 40+ years, you'd have to
>>> give a reference to the app note you're talking about. Most issues
>>> relevant to the era are addressed by the mfr using solutions that made
>>> sense for the applications of that time.
>>>
>>> The original mfr's app notes pre-date any electronic format (or the
>>> non-academic dissemination of Spice modeling) and may have suffered in
>>> the conversion process.
>>
>>On the contrary; TI's recently updated their TL494 datasheet, in fact! 
>>(They also added a layout section to the LM555 datasheet.  Go figure?)
>>
>>They've been updating a lot of their resources, it seems!
>>
>>Anyway, as we're talking TLxxx, I'm mainly referring to TI's appnotes.  But 
>>there are others, yes (and other errors :) ).
>>
>>
>>> Though they are unlikely to have been written
>>> by an 'intern' (author's names and sources are typically preserved),
>>> the usual precautions for typos in anything passing through the sales
>>> department are required.
>>
>>There are relatively few appnotes with authors on them, actually.  At least 
>>that I've seen.  LT seems to be a standout in that regard (indeed, their 
>>appnotes even have character, from time to time, especially the Jim Williams 
>>ones).  TI not so much.
>>
>>Pretty sure I've never seen an appnote that shows the author's name AND 
>>title / qualifications (not that you couldn't look them up separately, of 
>>course).
>>
>>And, yeah, I honestly doubt most appnotes are written by interns, but it's a 
>>lie I tell myself to make myself feel better, that a real engineer couldn't 
>>be so ignorant as to write such things.
>>
>>Tim
>
>I'm still interested in what was 'just wrong'.
>
>The earliest TL494 app note that was digitized at TI as SLV001 in 1998
>dates from 1989 print media, but it originated as Bulletin CA-198 by
>John Spencer published in 1978. The external latch is shown as fig27.
>
>The 1998 digitization for SLV001 was image-only, so there was little
>chance of 'extra' typographical issues being generated. This was fully
>re-edited for later revs to be text-searchable and was still basically
>the same information, at revD, in 2005.
>
>Double-pulse suppression was claimed in the part's print data sheet as
>early as 1983, but an effective latch is not present in the functional
>block diagram of the TL494's (SLVS074) specification sheet, to this
>day.
>
>RL

Tim just being his usual supercilious self >:-}
		
                                        ...Jim Thompson
-- 
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| STV, Queen Creek, 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'm looking for work... see my website.

Thinking outside the box...producing elegant & economic solutions.

"legg" <legg@nospam.magma.ca> wrote in message 
news:hm9grcl72nklrdhb686tmqdvti7nrp2uko@4ax.com...
> I'm still interested in what was 'just wrong'.

Remembered what it was:
http://www.ti.com/lit/an/slva666/slva666.pdf

(Which, speaking of, does in fact have an author.  The name shows up on 
prabook.com, "Analog applications engineer Texas Instruments India Private 
Ltd., since 2007".)

The schematic should speak for itself, but if you'd like to know what I 
spotted, let me know.

Tim

-- 
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com 

On Tue, 12 Sep 2017 18:00:28 -0500, "Tim Williams"
<tmoranwms@gmail.com> wrote:

>"legg" <legg@nospam.magma.ca> wrote in message 
>news:hm9grcl72nklrdhb686tmqdvti7nrp2uko@4ax.com...
>> I'm still interested in what was 'just wrong'.
>
>Remembered what it was:
>http://www.ti.com/lit/an/slva666/slva666.pdf
>
>(Which, speaking of, does in fact have an author.  The name shows up on 
>prabook.com, "Analog applications engineer Texas Instruments India Private 
>Ltd., since 2007".)
>
>The schematic should speak for itself, but if you'd like to know what I 
>spotted, let me know.
>
>Tim

Looks functional.

You may think he's incorrectly grounded the OC pin, but he's handling
maximum duty cycle and slow-start via DT pin bias.

The fault limiting will have issues, however.

Fighting the output emitter for control of the gate drive under
peak-current-fault conditions is a bad idea. If the gate drive
turn-off was latching, rather than just a pnp pull-down, or the
control supply wasn't bootstrapped, it could conceivably work; but
you'd be right in trashing that as a useful fault limiting circuit. 

It wouldn't prevent basic operation of a breadboard, though, and he
has pictures to prove it.

RL

"legg" <legg@nospam.magma.ca> wrote in message 
news:curgrc1p29fq757or574vnsci8a7b2jkc0@4ax.com...
> Looks functional.
>
> You may think he's incorrectly grounded the OC pin, but he's handling
> maximum duty cycle and slow-start via DT pin bias.
>
> The fault limiting will have issues, however.

A circuit that doesn't have functional limiting or fault protection, is not 
a functional circuit, sorry. :-)

Not if I'm reviewing it.


> Fighting the output emitter for control of the gate drive under
> peak-current-fault conditions is a bad idea. If the gate drive
> turn-off was latching, rather than just a pnp pull-down, or the
> control supply wasn't bootstrapped, it could conceivably work; but
> you'd be right in trashing that as a useful fault limiting circuit.

It would've been slightly more okay, if the clamp transistor were connected 
just after the series resistor.  It would have some hope of fighting the 
emitter output, then.

But you missed the best part: the LM339 is open collector.  There's no 
pull-up!


> It wouldn't prevent basic operation of a breadboard, though, and he
> has pictures to prove it.

Again, if there's a limit function, then you must also perform a test, to 
prove it is functional!

Short the output and watch the smoke rise. :)

(The implied irony being, if there isn't a limit function, you don't need to 
test it!  Well, that's actually fine -- as long as the end user _fully_ 
understands the consequences.  But, accident-prone users (which is everyone) 
aren't a good match for unprotected circuits, so I cannot abide such a 
conclusion.)

Tim

-- 
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com 

On Thu, 14 Sep 2017 06:19:38 -0500, "Tim Williams"
<tmoranwms@gmail.com> wrote:

>"legg" <legg@nospam.magma.ca> wrote in message 
>news:curgrc1p29fq757or574vnsci8a7b2jkc0@4ax.com...
>> Looks functional.
>>
>> You may think he's incorrectly grounded the OC pin, but he's handling
>> maximum duty cycle and slow-start via DT pin bias.
>>
>> The fault limiting will have issues, however.
>
>A circuit that doesn't have functional limiting or fault protection, is not 
>a functional circuit, sorry. :-)
>
>Not if I'm reviewing it.
>
>
>> Fighting the output emitter for control of the gate drive under
>> peak-current-fault conditions is a bad idea. If the gate drive
>> turn-off was latching, rather than just a pnp pull-down, or the
>> control supply wasn't bootstrapped, it could conceivably work; but
>> you'd be right in trashing that as a useful fault limiting circuit.
>
>It would've been slightly more okay, if the clamp transistor were connected 
>just after the series resistor.  It would have some hope of fighting the 
>emitter output, then.
>
>But you missed the best part: the LM339 is open collector.  There's no 
>pull-up!
>

Yeah, well, the protection cct doesn't function, period.

Odd to see a 2A schottky on a 3A flyback output.

RL