you but the 3-terminal regulator forces the VGS of the depletion FET to support its current and not the other way around. If you need an absolute guarantee, there is a simple (almost trivial) way to make the voltage differential across the 3-terminal stay above the minimum dropout threshold, which will be left as an exercise for the student.
I'm not a student, and you're a pompous old git.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
that gets you where you need to be.
If Fred had bothered to check the part data sheets, and not just swallow appnotes intact, he would have seen that the Supertex thing is flakey.
It has another big problem, two actually, but I'll, as fatheads Fred and Jim like to say, "leave it to the student" to figure out.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
worked
You don't understand depletion mosfets? They have some serious advantages in lots of situations. At least three people make them, so thay're not expensive or exotic.
I just designed an active capacitor bleeder for a laser driver. Serious amounts of energy are stored, and I want to caps to be discharged to zero volts in a reasonable time. A depletion fet does it.
Consider four ways to discharge a capacitor bank:
Envision the four discharge curves.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
78L12 that gets you where you need to be.
Explain to us "fatheads" just how is it flakey [sic]? (You misspelled "flaky" :-)
Which request you will ignore, because you fit the mantra, "Stupid is as stupid does".
I keep saying, and you, and many others, keep ignoring... the models provided by LTspice are "more perfect than nature", and I've provided examples. If you want some assurance of circuit performance, seek out models provided by the manufacturer, or a private source.
And also apply some mental reality checks. Simulations are only as valid as the quality of the models. Fortunately, for me, I/C foundries provide very accurate models, with a large support team to validate their accuracy. Jelly bean discrete part manufacturers rarely do. ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85140 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
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I love to cook with wine. Sometimes I even put it in the food.
78L12 that gets you where you need to be.
Sterling lecture. Now get practical and find the two additional problems (I've pointed out one already) with the Supertex 78L12 bootstrap.
Hmmm, there could even be one more!
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
78L12 that gets you where you need to be.
Well! As a start, Figure 10 says "78L05", NOT "78L12". Displaying, again, your deficiency in reading comprehension.
But, if you see problems, what don't you spell them out, rather than bloviating? You criticize others for being vague, yet you are the most obtuse poster in this group. Maybe it's you who is the "senile old git", huh ?>:-} ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85140 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.
78L12 that gets you where you need to be.
Fred, not I, pointed to the Supertex figure and suggested using a 78L12. Interesting suggestion, coupled with a stupid insult.
But that doesn't matter. The bootstrap, as shown, has several hazards with any
78Lxx.
It's incredible that you can't see even one of the problems.
Electronic designers need imagination, not to just conceive circuits, but also to imagine all their hazards.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
Where does "BOOTSTRAP" come from? It looks like this is a startup circuit rather than a standalone regulator, since when BOOTSTRAP comes on, it appears as though it will turn off the FET. (The voltages and Zener types aren't marked, so it's hard to be sure, but it sure looks like that's the intent.)
If the bootstrap were intended to improve the regulation of the MOSFET loop, it would be driving the top of ROFF1 rather than the output.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Larkin is throwing the typical "not invented by me" hissy-fit, how childish . There are any number of ways to make the Supertex circuit bullet-proof. T his, or anything obviously equivalent to it, takes care of the "That's OK, but it probably doesn't guarantee the 78L12 dropout voltage" problem. Please view in a fixed-width font such as Courier.
. . HV+ . | . | . +----- . | | . | [Ra1] . | | . | | . | | + V - . |_|| | \ z . depletion ||--+-----||| \ | . | | . | | . | V > V | . | + IO - z - | . | ------- | . | | | | . +----| 78LXX |----+----+--- . | | | | | . | ------- | | . === | === [Ra2] . | | | | . | | | | . ---+--------+--------+----+--- . . . .
Well, sorry to introduce discussion into this wonderfully artistic pissing contest, but I'll take that invitation.
Did I miss any?
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
There are any number of ways to make the Supertex circuit bullet-proof. This, or anything obviously equivalent to it, takes care of the "That's OK, but it probably doesn't guarantee the 78L12 dropout voltage" problem.
No, you do not want to do that. If the load gets disconnected, you'll be sourcing current into the output of the 78Lxx. The input will likely rise until Bad Things Happen. You'd have to add another zener at the output to prevent this, at which point you have 8 parts instead of the original 4.
BTW 78Lxx devices _stink_. Their ripple rejection is horrible compared to the 78xx or LM317L. I used to use them occasionally, having beguiled myself into thinking that they were just low-power 78xx, but then I actually read the datasheet. :(
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
That's what Ra2 is about, to sink the zener (or whatever is used) bias current. You're no more likely to require an OVP clamp in this circuit as in any other
78LXX circuit.
That is probably another non-issue here taken care of by the choice of input side capacitor to the 78LXX. The FET is operating in its active region so I would expect at least a few 10s of K-Ohms impedance between the HV+ and the
78LXX input.It's good to nitpick all the various failure mechanisms of any circuit, but just don't try to make out that the original Larkin kluge is some kind of failsafe innovation when it is even more vulnerable to failure than this one.
Figure 8
At 10 us, the fast stuff, rise and fall, get line-segment-y, which I don't trust. Some sub-10us oscillation could be lurking.
In the DOS days, I used to run ECA, which wasn't Spice based. It was fast and dumped errors like DIVIDE BY ZERO and CONVERGENCE ERROR but just kept going.
-- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
worked
-- Straw man. My point was that using them for panfilero's application is complete nonsense when it can be done with an LM4041 and three resistors.
worked
This is for my application. I never mentioned Panfilero in this thread.
This is MY application, MY thread, you moron!
amounts
This is MY application, MY thread, you moron!
(I find it's best to repeat things to morons.)
Yeah, electronics doesn't interest you.
-- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
I don't have a dog in this fight. JL's circuit was a reworked version of one dating back to the tube days, as he said himself, and similar ones have appeared in every one of those interminable Circuits Encyclopedias that people used to publish. (I had to buy a bunch of those a couple of years ago, in order to cite them as prior art against a really dumb patent. They're even more horrible than I remembered.)
The tube version would have been a lot more robust against transients and shorts and stuff, but its regulation would have been very poor by modern standards.
Why not discuss circuits, rather than getting into pissing contests? I mean, it's not as though Figure 10 in the IXYS app note is your own personal masterpiece or anything.
Back to the circuit. Using a voltage divider to protect the regulator requires fairly tight constraints on the component values vs the HV voltage, and you haven't shown any values. It also wastes a lot of power in general.
A zener would be very much safer, would waste no (additional) power at all in normal operation, and would protect against regulator failure as well.
And with all the HV transients potentially running round that circuit at turn-on, I wouldn't agree that it's unlikely to need an OVP clamp.
Shorting the HV supply to ground (e.g. some sensible tech discharging the capacitors before working on the equipment) could be exciting as well--inductive spikes everywhere, plus the usual 78xx failure mode when their inputs are shorted to ground.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
I think you pretty much covered it but I'll add to it :)
If the initial charge/transients on the drain to gate do not damage the reg output, the elevated voltage could force the reg into an unloaded state on the input and cause the fet to supply too much voltage for the reg input.
Depending on the form of transients, the cap on the input could charge if the duty cycles > 50%.
Just a thought..
Jamie
worked
-- Apologies. I got this thread mixed up with the: "low power voltage reference recommendation" thread where you introduced the rather humorous idea of using depletion mode MOSFETS as superfluous series pass elements for 8000 ohm loads drawing 1.5 milliamperes.
.MODELS
worked
You quit thinking when you reply to my posts. That's silly.
There was a suggestion to use constant-current diodes. Depletion fets are usually a better choice. If your input and output voltages are pretty much invariant, then use a resistor. If not, a current regulator is an option.
LND150/250 are pretty reliably about 1.6 mA Idss and are good for hundreds of volts. That can be handy at times.
That's a "two-bit DAC"
-- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
This IS a start-up circuit, it powers the switcher control chip (L6561) until the switcher generated power comes up and takes over.
Zo-o-o-om in :-) The voltages are marked. Much like in LTspice, my PSpice behavioral zener model lets you set Vzt @ Izt and the Rs, just by double-clicking the part and a dialog comes up.
It's just for start-up. But the regulation is excellent, Q9, and DZ9 comprise a cheapy TL431, a part the customer didn't have on-hand.
The L6561Power block piece-wise-linear models the V-I curve of the L6561 as it powers up. ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85140 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.
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