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From: Tim Williams on 25 Feb 2010 13:05
"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message
news:e5ado5hhn2964dd3qg4j3amqs3hcg0bdd2(a)4ax.com...
>>Bah, common base is great for saving parts. :)
>> http://webpages.charter.net/dawill/Images/CC_Buck.gif
>
> Hey, I can do that too!
>
> ftp://jjlarkin.lmi.net/Inverter.jpg

Pffbt... mine has fewer parts, and way fewer total transistors. ;-)

Size? Ohh, about the same I guess, since both can be made from SMT parts,
with output limited by their power dissipation. The FET is more efficient
of course.

If CC_Buck were actually "CV_Boost", it would look more like:
http://webpages.charter.net/dawill/Images/Blocking%20Oscillator%20Supply.gif
which is almost exactly what you've done. Invert all the polarities and it
is exactly what you've done. But I like to save on components by putting a
wire jumper around the inductor.

For best results, the error amp (grounded base strikes again!) ought to be
replaced with a bandgap reference.

It's a shame they don't make noninverting TL431's. As is, the anode carries
output current, and the offset is -2.5V, not as nice. Compensation would be
a curious affair though...

> A neat logic level shifter is TTL-resistor-PNPemitter with the PNP
> base grounded, collector going to somewhere negative.

LT did it to test their LT1016 (pg.7 of the datasheet). Although they used
a beefy NPN instead.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms


From: Joel Koltner on 25 Feb 2010 13:23
"Tim Williams" <tmoranwms(a)charter.net> wrote in message
news:hm6e50$3ss$1(a)news.eternal-september.org...
> If CC_Buck were actually "CV_Boost", it would look more like:
> http://webpages.charter.net/dawill/Images/Blocking%20Oscillator%20Supply.gif
> which is almost exactly what you've done.

Yabbut.. in small production quantities, an inductor is a heck of a lot more
attractive than a transformer -- especially if it's not an off-the-shelf
transformer.

From: John Larkin on 25 Feb 2010 13:37
On Thu, 25 Feb 2010 12:05:18 -0600, "Tim Williams"
<tmoranwms(a)charter.net> wrote:

>"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message
>news:e5ado5hhn2964dd3qg4j3amqs3hcg0bdd2(a)4ax.com...
>>>Bah, common base is great for saving parts. :)
>>> http://webpages.charter.net/dawill/Images/CC_Buck.gif
>>
>> Hey, I can do that too!
>>
>> ftp://jjlarkin.lmi.net/Inverter.jpg
>
>Pffbt... mine has fewer parts, and way fewer total transistors. ;-)
>
>Size? Ohh, about the same I guess, since both can be made from SMT parts,
>with output limited by their power dissipation. The FET is more efficient
>of course.
>
>If CC_Buck were actually "CV_Boost", it would look more like:
>http://webpages.charter.net/dawill/Images/Blocking%20Oscillator%20Supply.gif
>which is almost exactly what you've done. Invert all the polarities and it
>is exactly what you've done.

Not exactly. I'm using a Schmitt RC oscillator that sets a default
startup duty cycle, and then using a feedback loop to back off the
duty cycle when the output hits -12.


But I like to save on components by putting a
>wire jumper around the inductor.

YIKES! The charging current into C1 is beta limited! And a little
overshoot on the output could fry somewhere between one and three
transistors.

But I confess I do like blocking oscillators. But custom magnetics are
a pain, so I tend to avoid them in favor of more complex circuits that
use standard parts.

>
>For best results, the error amp (grounded base strikes again!) ought to be
>replaced with a bandgap reference.

I'm using a +5 supply that I have already. It kind of soft starts,
even nicer.

John

From: Jim Thompson on 25 Feb 2010 13:48
On Thu, 25 Feb 2010 10:37:12 -0800, John Larkin
<jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote:

>On Thu, 25 Feb 2010 12:05:18 -0600, "Tim Williams"
><tmoranwms(a)charter.net> wrote:
>
[snip]
>>
>>If CC_Buck were actually "CV_Boost", it would look more like:
>>http://webpages.charter.net/dawill/Images/Blocking%20Oscillator%20Supply.gif
>>which is almost exactly what you've done. Invert all the polarities and it
>>is exactly what you've done.
>
>Not exactly. I'm using a Schmitt RC oscillator that sets a default
>startup duty cycle, and then using a feedback loop to back off the
>duty cycle when the output hits -12.

Sort of like I was doing _36_years_ago_...

http://analog-innovations.com/SED/FlybackDC-DC-Converter.pdf

except that the inductor was constant charge, with rate backing off
when set-point was reached.

[blow-hard-ego-trip-stuff snipped]

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| 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.
From: JosephKK on 26 Feb 2010 05:45
On Tue, 23 Feb 2010 09:21:22 -0600, "Tim Williams" <tmoranwms(a)charter.net> wrote:

>> Early effect. Change of collector current with collector voltage.
>>
>> Cure it by dropping several volts in the emitter path... add R's in
>> series to Q1:E, Q2:E, Q13:E, Q12:E, etc.
>
>Emitter resistors help, or you can cascode it (Wilson mirror, etc.), or
>both.
>
>Why use Q8, 9, 12 and 13, why not run Q2 straight into R40?
>
>Why all the resistors? You can remove more than half with no change in
>performance. R15, 16, 21, 22, 23, 37, 39 and 40, which basically leaves
>R12, 19, 27, 28 and 48.
>
>Tim

Offhand, i would guess they are there to say within the Vce and Vgs ratings of the transistors.
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