Circuit Challenge of the Day

The following circuit...

http://analog-innovations.com/SED/Ra..._Amusement.pdf

is a ramp generator.

It is easy to see how the upper trip point circuitry causes discharge
of the ramp.

But what causes the turn-around at the bottom?

...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 | |
| Voice480)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 wrote:
Circuit Challenge of the Day

The following circuit...

http://analog-innovations.com/SED/Ra..._Amusement.pdf

is a ramp generator.

It is easy to see how the upper trip point circuitry causes discharge
of the ramp.

But what causes the turn-around at the bottom?

...Jim Thompson
As the collector current of Q1 drops to zero, its VBEsat drops below the
level needed to keep Q4 turned on, due to that 200 ohm resistor dropping
100 mV.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net

On Fri, 18 Dec 2009 12:46:20 -0500, Phil Hobbs
wrote:

Jim Thompson wrote:
Circuit Challenge of the Day

The following circuit...

http://analog-innovations.com/SED/Ra..._Amusement.pdf

is a ramp generator.

It is easy to see how the upper trip point circuitry causes discharge
of the ramp.

But what causes the turn-around at the bottom?

...Jim Thompson
As the collector current of Q1 drops to zero, its VBEsat drops below the
level needed to keep Q4 turned on, due to that 200 ohm resistor dropping
100 mV.

Cheers

Phil Hobbs

Shhhhhh !-)

...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 | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

Help save the environment!
Please dispose of socialism properly!

Huh...

Q6 should "never" turn on, since it's hooked to a "current mirror". Q5 and
Q7 Vbe's match Q6's, so it would only turn on if Q7 Vce = 0.

Of course, at Vce = 0, beta is ****, so it's no longer a "current mirror"
either.

That, and as Hobbs said, make this a confusing circuit to anyone who thinks
"Vbe == 0.7V".

I forget if Eber-Molls even models Vbe vs. Ic.

Tim

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

"Jim Thompson" /Snicker
wrote in message ...
Circuit Challenge of the Day

The following circuit...

http://analog-innovations.com/SED/Ra..._Amusement.pdf

is a ramp generator.

It is easy to see how the upper trip point circuitry causes discharge
of the ramp.

But what causes the turn-around at the bottom?

...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 | |
| Voice480)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 Fri, 18 Dec 2009 12:15:25 -0600, "Tim Williams"
wrote:

Huh...

Q6 should "never" turn on, since it's hooked to a "current mirror". Q5 and
Q7 Vbe's match Q6's, so it would only turn on if Q7 Vce = 0.

Of course, at Vce = 0, beta is ****, so it's no longer a "current mirror"
either.

That, and as Hobbs said, make this a confusing circuit to anyone who thinks
"Vbe == 0.7V".

I forget if Eber-Molls even models Vbe vs. Ic.

Tim

You need to spend some time refining your circuit analysis/design
tools.

Don't give up your day job ;-)

...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 | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

Help save the environment!
Please dispose of socialism properly!

"Jim Thompson" /Snicker
wrote in message ...
Circuit Challenge of the Day

The following circuit...

http://analog-innovations.com/SED/Ra..._Amusement.pdf

is a ramp generator.

It is easy to see how the upper trip point circuitry causes discharge
of the ramp.

But what causes the turn-around at the bottom?

Years ago I put together a circuit for messing with random inductors, it was
based on a bistable and the "off" state was tripped by the rise to
saturation current in the driver transistor. The fun part was sensing when
the flyback voltage had peaked and was on its way back, to trip the bistable
on state.

The circuit would be easily recognisable if I could find it - it was a dead
bug/bird's nest type thing, but it seems to have vanished without trace -
I'm pretty sure I documented the development, but I can't find that either.

ian field wrote:
"Jim Thompson" /Snicker
wrote in message ...
Circuit Challenge of the Day

The following circuit...

http://analog-innovations.com/SED/Ra..._Amusement.pdf

is a ramp generator.

It is easy to see how the upper trip point circuitry causes discharge
of the ramp.

But what causes the turn-around at the bottom?

Years ago I put together a circuit for messing with random inductors, it was
based on a bistable and the "off" state was tripped by the rise to
saturation current in the driver transistor. The fun part was sensing when
the flyback voltage had peaked and was on its way back, to trip the bistable
on state.

The circuit would be easily recognisable if I could find it - it was a dead
bug/bird's nest type thing, but it seems to have vanished without trace -
I'm pretty sure I documented the development, but I can't find that either.


Sounds a bit like a Royer converter.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net

"Jon Kirwan" wrote in message
...
snip
I actually like the way it works. I just didn't like the way Jim drew
the darned thing.

I still don't quite like it -- I'd like to see Q3 and Q4 together, since
they're basically an RTL NOR gate (Q4 having a peculiar turn-off voltage).
Then invert it with Q2, feed back to Q4 and drive Q1, and you have your
driver part, from left to right.

Tim

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

On Fri, 18 Dec 2009 20:07:15 -0600, "Tim Williams"
wrote:

"Jon Kirwan" wrote in message
.. .
snip
I actually like the way it works. I just didn't like the way Jim drew
the darned thing.

I still don't quite like it -- I'd like to see Q3 and Q4 together, since
they're basically an RTL NOR gate (Q4 having a peculiar turn-off voltage).
Then invert it with Q2, feed back to Q4 and drive Q1, and you have your
driver part, from left to right.

Well, draw it up the way you'd like. I'd love to see that, if you can
afford the moment to do it. Honestly. It might help me do a better
job thinking about other things to see a little better about
redrafting stuff like this. Anyway, I'd appreciate your shot at it if
you feel like trying a hand at it. (I don't agree about your wish for
Q3 and Q4, right now, but if you draw it up the way that makes better
sense to you I might change my mind about it and learn something.)

Thanks,
Jon

"Jim Thompson" /Snicker
wrote in message ...
You need to spend some time refining your circuit analysis/design
tools.

Don't give up your day job ;-)

Tools? What, did you actually think I'd waste a simulation on your silly
ideas? ;-)

BTW, my "day job" is doing well: I've already sold a number of induction
heater kits. :-) See the latest update on my website.

Tim

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

On Sat, 19 Dec 2009 00:41:34 -0600, "Tim Williams"
wrote:

"Jim Thompson" /Snicker
wrote in message ...
You need to spend some time refining your circuit analysis/design
tools.

Don't give up your day job ;-)

Tools? What, did you actually think I'd waste a simulation on your silly
ideas? ;-)

"Silly ideas"? That circuit in I/C form, more than thirty years ago,
was in several different automotive ignitions.... used to time dwell.
In I/C form the ramp started essentially from zero (I could scale
transistor areas). In I/C form it was triggerable rather than
continuous, thus no R2, Q3, Q6.

That was a circuit I remembered, wanted to use again, pulled it from
archive, then couldn't figure out how it worked ;-) Stewing over it,
finally it dawned, so I made it up as a teaser to see if anyone could
figure it out. So far only one person :-(


BTW, my "day job" is doing well: I've already sold a number of induction
heater kits. :-) See the latest update on my website.

Tim

...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 | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

Help save the environment!
Please dispose of socialism properly!

On Sat, 19 Dec 2009 08:51:01 -0700, Jim Thompson
/Snicker wrote:

snip
That was a circuit I remembered, wanted to use again, pulled it from
archive, then couldn't figure out how it worked ;-) Stewing over it,
finally it dawned, so I made it up as a teaser to see if anyone could
figure it out. So far only one person :-(

Oh, more than one person. But you don't read my posts. So you
wouldn't know. Regardless, I enjoyed this thread from you and thanks
for adding it.

Jon