Isn't a low valley current what you want here? In that case Rg is in the several hundred kohm to mOhm range. I've never built something like this with a UJT but I think it would work to generate the bias voltage from the voltage across your base capacitor, without needing any helper supply or fancy charge storage.
-- Regards, Joerg http://www.analogconsultants.com/
Have a look at these sketches:
Triggers on when zener breaks down and latches on until runs out of current limit. The first one I combined trigger with limit sense but the
100k in the base causes a delay in limit action and a spike in LED current. The second sketch with those functions separated out is better.Ordinary 22-47V volt zener diodes are amazingly bad in the micro-amp region. A reverse biased base-emitter junction is very much better at such low currents than equivalently priced zeners. The breakdown voltage is anywhere between 6 - 8V but that doesn't matter in this application also helps keep the number of different parts down. I read somewhere that the BE junction zener tempco is about +2mV/C so if one uses the CB diode -2mV/C you get a cheap temp compensated low current reference, at somewhere 6-8V.
piglet
Holding current is what it is all about. Easy to define if you actually understand device-level circuit design.
I posted this before...
VoltageIndicator(SED).pdf
on the S.E.D/Schematics page of my website.
Who can tell me what Q6 does? ...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.
It isolates the pseudo-SCR/PUT from the supply during the flash event to guarantee reliable turn off. Saves messing about trying to fiddle with holding currents. A neat solution. Thank you.
It will also limit c1 charge rate if the available supply current is higher than Vbe/30k.
What is C2 for please?
piglet
More precisely, it keeps the charging current from ever exceeding the holding current so that the "pseudo-SCR" dumps into the LED, then always releases.
You're welcome.
Slows turn on of dump circuit, ensuring that "pseudo-SCR" has had time to latch. ...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.
Which implies a static latch state.
-- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Doesn't imply anything. You choose to limit the charging current to be less than the holding current, once it triggers... guarantees that it releases at the "valley".
If you take issue with that analysis, please elaborate with supportive math >:-} ...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.
That may exist. A long time ago the had shunt regulator tubes for the CRT anode in color TVs. Later they had some solid state equivalent, finally they just directly used a voltage divider and used normal regulated supply techniques. It is the solid state regulator that i would like a look at; perhaps some of them have more than 2 terminals.
Don't need math for something this simple.
Just imagine Q1-Q2 latched at a few uA and 0.6 volts or so. Q4 is on but the drop in the LED is too much to divert current from the latched pair. Q6 is off. It's hung.
Any such circuit that needs a cap to make it work probably has hangup hazards. I don't like analog or digital or software systems with hangup states; sooner or later they manage to get into them.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation
out
volt
I will have to look at them. 12 V may be more useful for this circuit though.
be
or 10-chip
set the
fets. It
Good point. I think it simplifies my idea a bit. Standard HV power FETs go well past 1 kV. 1 moderate resistor and a constant current FET stack should get the maximum range with useful current for the blinker cap storage circuit. Do you want more explanation? What about LTSpice models for all the power FETs (even kind of crappy ones)?
?-)
to
Not even wrong. Jumping at delusions.
?-)
The circuit sketch I posted yesterday (Betterblinker.pdf) does have a hang state if the supply current limit is very low, as in low tens of uA but snaps out of it once the operating current range is reached.
piglet
Well, of course: a van de Graaff generator. Compliance actually goes higher (few megavolts) before insulation breakdown becomes a major issue.
I guess you _do_ need to run the math. As piglet spotted, and I further explained, Q6 has an important function. ...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.
Everyone is wrong... except Larkin >:-} ...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.
As I pointed out, at a few uA, the latch is locked up but Q6 is off. It appears to work in simulation because C2 gives it a temporary boost and memory. But after C2 is used up, it has a state where it's hung. I don't want my HV indicator to have a hang state. If it hangs at low current, and then the current is ramped up, I think it stays hung; overall feedback is negative, from both Q4 and Q6.
Another feels-good async hairball.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation
Circuits don't care about our opinions. They do what they do. Yours can hang.
I detailed a hang state. Say something about it. Please say something better than "it can't get there" or "it works in simulation."
The blinker problem turns out the be seriously difficult.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation
It's a bit fiddly, as you suspect. Motorola had a good app note on using PUTs that went into all of it.
It's doable, but it's why I prefer the complementary configuration I posted--it's solid.
If you ensure the amplifier stays linear, and has gain >1 with appropriate phase shift at some frequency (preferably the desired one!), it'll run. My gadget does that.
PUTs can latch ON with gain
How can it hang? The LED stays lit until the current has dropped below the valley current, then the UJT quits conducting just like an SCR does when its hold current is no longer met. Now the voltage across the charge cap rises again until the programmed firing voltage is reached -> next flash cycle happens.
-- Regards, Joerg http://www.analogconsultants.com/
There's a good treatment here, pg. 42-48, and pg. 132-136 has nifty application circuits:
The difficulty with making your own is that a bunch of stuff varies with hfe(Q1) * hfe(Q2), which is mighty squirrely over temp.
Cheers, James Arthur
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.