Any time there is a closed-loop circuit with an emitter-follower directly feeding a low ESR cap, instability or oscillation can result. I have fixed this problem a dozen times, even on production medical equipment. In the old days, 4.7uf ceramic caps didn't exist and electrolytics or tantalums worked fine on any voltage regulator due to their high ESR of 1 ohm or more. Ceramics have very low ESR. and electrolytics had high ESR. It turns out that if the ESR is low enough, many regulators and follower circuits will oscillate. New regulator designs are aware of this. Old part data sheets had to be modified to specify a minimum ESR. Well, you can't guarantee a minimum ESR of a cap, so good luck. For this circuit, try a 1 ohm R in series with the cap. Spice model a closed-loop op-amp, NPN, and a cap, Then mess with the cap, it's ESR, the load, etc. and see what happens to the step response. Like me, you too will cringe every time you see an emitter follower driving a cap. It has nothing to do with the breadboard. It's just a marginal design that looks OK at first glance.
"Amplifiers become Oscillators and Oscillators become Amplifiers" such is the lament of an Analog Design Engineer. Those push-pin type breadboards are notorious for have tons of capacitance between strips. I would build up the prototype on a piece of vector board to eliminate that possibility.
Surprising that you would expect this to work at all on a breadboard. Read the datasheet: the part is extremely sensitive to series resistance in the output capacitor leg, not to mention that the suggested layout is there for a reason.
I am an FAE for Linear Technology. the 6655 is a fine reference and there is nothing wrong with the datasheet. I would suggest that one examines the parasitic components associated with a breadboard. Please build the circuit on a perfboard with a plane and then comment on the circuit performance. Think about the plate to plate capacitance inside of that white brick you layed this out on before you disparage the component. I have used it in many instances without a single incident. With the current round of ICs on the market I would contend that the usefulness of the breadboard is nearing its limit,
Your NPN Power transistor has a huge amlification. You get a phase turn beyond 180°: So you need to reduce amplification for high frequencys. This can be done eg, with a RC Pass. I would recommend using a 2 cascaded RC Pass. Another thing that might produce in a later stage problems is your impedance converter, as it sits in the feedback path. A golden rule for feedback loop is. as short as possible.
I agree that the NPN transistor has a huge CURRENT amplification. But it's VOLTAGE amplification is 1 (one) as it is used as an emitter follower. I do not see how you would get a 180° phaseturn that way. What I suspect is that the high gain of the internal error amp causes the loop gain to be too high at the piont where you get overall 180° phaseturn which is caused by all the capacitances present in and outside the amplifier.
Peter-Paul Vervoort the current amplification translates by ohms law to a voltage (sense resistor). You wont get the phase turn away, but you can get the amplification below 1 by a rc pass- and the loop will be stable.
One way to eliminate any possible noise from the power supply is to use a battery. This is something I have been exploring using the LTC6655 and found it made a notable difference to the noise on the output. Also breadboards suck for this kind of thing. Parasitic everything, everywhere.
You cant use the ground like this (this IC has two different grounds, check the datasheet block diagram, it would be better if you used the one which controlling the internal reference only and the other one tie it with the circuit ground, it might work). C2 here became a feed forward capacitor as the buffer is not an ideal current source/sink, it should be connected to the real ground in your circuit (and here it will add some delay as your cicuit is a current sense feedback). Another issue, the diode will provide his own feedback with a value related to the current flowing through it (non linear problem). Read about PID controllers....................... Here is my suggestion: Use instrumentation amplifier, "Inputs" on the sense resistor, its "Output" connected to "Vout_s"; and the gain of the Ins. Amp. can be adjusted for desired current output. And here you can use much lower sensor resistor value (suggested 1 to 100 mohm) :)
Good on, Ive found that you learn more by fails and play about trial and error. when working for Ekco's in my distant past and working with the old lm741 op amps this was about 1980, you always had to have a cap in the feed back to stop osc.
This is the problem with solderless breadboards in general. You're going to get capacitative coupling & lead inductance issues. For precision stuff, you need to go with a dead-bug or custom PCB prototype right from scratch.
I have had similar problems with discrete voltage regulators, in this case I think the breadboard is doing you no favours, you may also have issues with rf pickup. Good to see intelligent comments for a change.
There is no Problem with the datasheet application. You just did not built up the circuit which is in the data sheet. It says explicitly to use the LTC6655-2.5 but you used the LTC6655-1.2. They use 4.7 uF at Output, you use 10 uF. The scope thing is a bug for sure. Btw you should have a look on Graph 12 in data sheet. Plus I guess you crashed the IC by your original circuit which is catastrophic! However the worst mistake you made is that you simply forgot to connect pin 8 to ground.
I can see how it might be interpreted as a bug (the scope thing at 12:06), but if you think about it, its the firmware trying to replicate what would be seen on a CRT on the LCD. It appears to be looping to a buffer between LCD refreshes, so that when the LCD does refresh, it displays a better representation of what would have appeared on a CRT.
This time Dave didn't made a good enginerring work: 1) Noise and OSCILLATIONS (which is mostly what is happening in the circuits he has breadboarded) are not the same thing. 2) You cannot simply ignore the loop frequency response of the error amplifier inside the LTC chip before tweaking the reference design, 3) It is much easier to blame the IC than your own breadboard and test set-up, but definitely not the most professional approach.
***** You are absolutely right on your comments and provide some common ground so that I now can also quite agree with you! Thanks for sharing your point of view.
A capacitor (I would try10 UF Tantalum) from the op-amp (pin6) to ground may have fixed it. The data sheet says pin 4 must be connected to a noise-free ground plane.
Nowhere in the application note does it suggest using the the ground in this fashion, which may explain why it doesn't work. It would have been safer to build it as a precision reference and follow it with a current source. When I started in R&D, I was told in no uncertain terms to never ever use one of those plug in things again. Design the thing and get pcbs made, then sort it out. Good advice, since its going to end up on a pcb, and the time you spend debugging a lash up is wasted.
I agree that this type breadboard may be a problem. There is parasitic capacitance caused by the pin to pin coupling between the bus bars. You can see the bus bars if you remove the paper covering on the bottom of the breadboard. Bar to bar coupling is likely enhanced (more capacitance) by the metal mounting plate that some breadboards sit on. This is bad for high frequency circuits. Although time consuming - hardwire the circuit on a bare copper PCB or make a PCB.
Esr of the output cap being a contributor to stability issues in linear regs ( same feedback loop stability issue here), a Tantalum cap rather than a poly may have been the way to go, just a bargain basement electrolytic has solved similar issues for me.
Great Videos Dave but i would have liked you to bring up more of your tutorials on different techniques or microcontroller environment or just the "fundamental friday" cause for us guys who are not Engineers in electronics but starting out enthusiasts it would be great help
I'm a long way from an expert but I'd have money on this sort of percision being very hard to achieve using a breadboard setup. Having this on a well designed and manufactured pcb would help significantly in my unqualified unasked for opinion.
My best guess on what could it be happening, is actualy the wires used to build the circuit on the protoboard,, they are long enough to behave as an antena, hence, inputing parasitic signals to a precission circuit like this, you will never find a precission refference built like this, you need a lot of shielding and higly conductive , short traces between components, this would be at least my guess,, i've had problems with this and it's almost imposible to get rid of some of that ripple, BTW love your videos Dave :)
When some oscillation is an issue my guess is that it is caused by parasitic inductances of the breadboard. I tried once making some boost converter from scratch (with no dedicated IC) and it just couldnt work, the efficiency was well below 50% and I couldnt pinpoint the issue untill I did the exact same circuit with the components I tried on a prototyping board and it works just perfectly with efficiency up to 90%. Turns out breadboard can be a real pain if you deal with high frequency ICs.
I was always baffled Dave rarely talks about nixies.. I guess it's just one little electronic thing, but they have captivated the internet's electronics forums for quite some years now!
***** Well, you're right that vintage electronics appeals to young people. No need to use buzzwords like retro, or Maker. Jeez, does anyone outside of marketing even use those words XD? However, older visitors who get to see my nixie tube clocks also have no idea what it is and have never seen it before. AKA the obscurity of USSR technology can appeal to all ages. I still think nixies are magic though.. The technology isn't that amazing, but the story that I can tell people is great. Soviet tech, production stopped in the late 70s early 80s, consume almost no power, resurrected from the grave by enthusiasts, found in old warehouses in eastblock countries.. etc. They have appeal, and I like it
I think you're going to find it completely boring. There's some neat stuff in there for sure, but most solid-state transmission systems are just a bunch of FETs and a combining backplane. Now if he got his hands on a tube rig, those are fun.
Haven't seen part 2 (yet), but at a guess: Too much gain introduced by the external transistor. That's why the darlington is even worse. Beta varies widely, so the particular 2N2222 might have very high beta/hfe. Use a lower gain transistor, or reduce the feedback proportion. Control systems: Oscilliations almost always means gain is too high.
The problem could be exactly the no load configuration: It could well be, that when you put in the NPN-Transitor you have an configuration which requires an minimum load current. Look at one thing in the datasheet in particular: "VOUT Force Pin. This pin sources _and sinks_ current to the load." With the NPN Transistor in Series, the circuit can not sink any current, but the Error Amp will try to do so when VOUT Sense is to high ever so slightly. But as an NPN Transistor is in Series, VOUT Force will go down without directly affecting the the sense voltage. Then the current of the VOUT Sense Pin (the sense pin is a voltage divider) will reduce VOUT Sense over time, till VOUT Sense is too low and then the error amp has to go back from a lower voltage back to a higher voltage. Granted: If the sink capability of the voltage reference is the problem, the application circuit in the data sheet is a joke. One of the differences between a voltage regulator and voltage reference is the ability to source _and sink_ current. If that is a problem for an "typical application" then it is not an typical application for a voltage reference.
Good Stuff! Maybe lower out coupling Cap ESR will help? Newer products call for some pretty exotic stuff. Is it possible such HF noise could be caused by input damage by heat? Who knows.. Thanks for the vid!
And there i was eating up the reference designs from datasheets with a golden spoon thinking they came from the gods of electronics. Seams quite straightforward to fix tho, just make your own error amp so that you can add in caps into it to slow it down so its stable, if done right it works well even on breadboards.
First off I'd like to say I've learned tons just by watching your videos Dave but I'm still a complete novice with this stuff . Just out of curiosity, I see that there is a jumper between H12 & J11 connecting pins 3 & 4 of your LTC6655 but those pins are not defined on the datasheet. Is it possible that may be related to some of the oscillations you are seeing in the output of the module? Also, I noticed that the diode did not appear to be attached to anything. :)
Can't you just whack on a huge value electrolytic capacitor on the force output, sense output, and output of the transistor? those MKP and ceramic/film caps ate low values, baybe larger values work better. Is it possible to reduce the internal gain of the feedback loop? maybe a voltage divider on it's sense?
Any chances you can take a few minutes to share how large power inverter companies make keep the peak to peak whintin the voltage parameters? I'm trying to make my own power inverter, and don't know how to make sure I don't finish with a really large back emf feedback that will destroy all my equipment
Could the nastiness have come from MAKING the opamp fit the adapter? I ask because I have a few ATTiny85s that I bought the wrong sized DIP adapters for.
COUNTERFEIT!...Mr. Chips. Ask me how I don't know. I've spent years over promising and under delivering. I know how to do it wrong. Cheers. Micro Image "We've Upped Our Quality, Now Up Yours". ❤
It seems like you have too much capacitance in the feedback loop. Since you are adding gain to your loop with the final transistor you want to be careful to not add any kind of delay I'm the feedback loop such as would result from stray capacitance. As was said in another comment it's likely coming from the breadboard itself. Sounds like an opportunity for dead bug and rats nest prototyping.
Obviously you're missing the point of what Dave is trying to achieve. A 1 Amp cell phone charger provides something between 4.5 V to 5.5 V to charge something. The current will be whatever the phone or load will take upto 1 A, so The current can be 0 A to 1 A. Such a charger behaves as a voltage source. Dave tries to make something that will deliver 1.000 A as precisely as possible independant of the voltage (within practical limits of course). This is called a current source. It is intended for electronic measurements, not charging your phone.
Uh ok, whatever. Some of these home made kits are ridiculous because you can already order the boards or go to rat shack and get one. Maybe if you are using a Raspberry Pi on your car multimedia head unit like bored1980 does and you need more power to run more then 2 usb devices with it.
nice videos you have there! ..if you get an ascillator somewhere you don't want .. you need to cut or reduce the feedback or reduce the amplification .. or maybe add some delay or phase shift to stop it .. the next old video seems to know how to make an oscillator (LC) .. to stop that you do the reverse! .. or remove some C which makes it to oscillate!;) --> ua-cam.com/video/a8casNPDvI4/v-deo.html
funny that in USA the current flows reverse direction compared to the situation here in Europe .. I don't know how the situation is in Australia? Here the current always flows from the positive voltage to the negative pole (and the electrons flow reversed) .. at least in old US videos it seems to be a common "local" fact that electrons and current flows the same direction (from - to +) .. very strange? haha!:)
What am I missing? You completely changed the circuit, used a created gnd from an op-amp output, then claimed that the application note was faulty. You made two grave errors. One- you think that an op-amp output is the same impedance as the GND in the circuit, and 2, when you plugged in the darlington you changed the loop gain which is part of the stability of the amp. I don't think the breadboard is the problem. To claim that the application note circuit doesn't work, you should actually test the application note circuit. In this case you are testing your assumptions and claiming that the application note was faulty. Sorry, I love your videos except not this one.
Oops, I did watch it, but now I re-watched it because of your question. Thank you, I don't think I noticed that part where he repeated the original circuit the first time through. However, I am not sure he really did correctly recreate the app-note circuit. He claimed to have re-run it, but I don't see C2, the 4.7uF cap in his "repeating original" circuit at 9:38 in the video. Just because he said that it shouldn't need caps NEAR the circuit and he wanted to test it that way, is he using the cap that is still hooked up to the other circuit? The other circuit still looks powered. And if he did duplicate it, but failed to put the two caps close to the circuit, why did not not then put them close and duplicate the test? I think he just plain forgot or did not include C2 thinking that it was just some noise reducing component. Claiming that the app note circuit does not work is somewhat serious and I have made tech support complaints when I found what are essentially flaws in the data sheets. Any decent company will act on a data sheet error. But, you have to make a good attempt at documenting the problem first. It is true that App note circuits don't always work, but I have a lot more faith in LT app note circuits than TI app note circuits for example.
Any time there is a closed-loop circuit with an emitter-follower directly feeding a low ESR cap, instability or oscillation can result. I have fixed this problem a dozen times, even on production medical equipment. In the old days, 4.7uf ceramic caps didn't exist and electrolytics or tantalums worked fine on any voltage regulator due to their high ESR of 1 ohm or more. Ceramics have very low ESR. and electrolytics had high ESR. It turns out that if the ESR is low enough, many regulators and follower circuits will oscillate. New regulator designs are aware of this. Old part data sheets had to be modified to specify a minimum ESR. Well, you can't guarantee a minimum ESR of a cap, so good luck. For this circuit, try a 1 ohm R in series with the cap.
Spice model a closed-loop op-amp, NPN, and a cap, Then mess with the cap, it's ESR, the load, etc. and see what happens to the step response. Like me, you too will cringe every time you see an emitter follower driving a cap. It has nothing to do with the breadboard. It's just a marginal design that looks OK at first glance.
You forgot to take into account the quantum vector polarization of the electrostatic recombination impedance.
:O
wat
"Amplifiers become Oscillators and Oscillators become Amplifiers" such is the lament of an Analog Design Engineer. Those push-pin type breadboards are notorious for have tons of capacitance between strips. I would build up the prototype on a piece of vector board to eliminate that possibility.
Input and Output directly to ground.. Just ruins your day... Dave, you're a riot! Your videos are informative and entertaining! 7:25 now
You might try baking the LTC6655 overnight at around 100°c. I do it on all surface mount IC's, it seems to stabilize them after soldering.
I like watching these videos where you go through circuits from theory to practise. I don't understand everything but little by little..
Surprising that you would expect this to work at all on a breadboard. Read the datasheet: the part is extremely sensitive to series resistance in the output capacitor leg, not to mention that the suggested layout is there for a reason.
I am an FAE for Linear Technology. the 6655 is a fine reference and there is nothing wrong with the datasheet. I would suggest that one examines the parasitic components associated with a breadboard. Please build the circuit on a perfboard with a plane and then comment on the circuit performance. Think about the plate to plate capacitance inside of that white brick you layed this out on before you disparage the component. I have used it in many instances without a single incident. With the current round of ICs on the market I would contend that the usefulness of the breadboard is nearing its limit,
I agree "protoboard" is likely a big problem. See comments here from bdd4.
Precision requires a different type of set up a breadboard is no go!
Oh, app notes. Always expecting you to have 5 different grounds all on separate planes.
So the LTC6655 is not 'dead-bug' style.. It's 'squashed-bug' style :)
Great vid Dave
Your NPN Power transistor has a huge amlification. You get a phase turn beyond 180°: So you need to reduce amplification for high frequencys. This can be done eg, with a RC Pass. I would recommend using a 2 cascaded RC Pass.
Another thing that might produce in a later stage problems is your impedance converter, as it sits in the feedback path. A golden rule for feedback loop is. as short as possible.
I agree that the NPN transistor has a huge CURRENT amplification. But it's VOLTAGE amplification is 1 (one) as it is used as an emitter follower.
I do not see how you would get a 180° phaseturn that way. What I suspect is that the high gain of the internal error amp causes the loop gain to be too high at the piont where you get overall 180° phaseturn which is caused by all the capacitances present in and outside the amplifier.
Peter-Paul Vervoort
the current amplification translates by ohms law to a voltage (sense resistor). You wont get the phase turn away, but you can get the amplification below 1 by a rc pass- and the loop will be stable.
One way to eliminate any possible noise from the power supply is to use a battery. This is something I have been exploring using the LTC6655 and found it made a notable difference to the noise on the output.
Also breadboards suck for this kind of thing. Parasitic everything, everywhere.
Stick 100pF between base+emitter of pass transistor so high frequency feedback isn't compromised by bandwidth
of the pass transistor?
You cant use the ground like this (this IC has two different grounds, check the datasheet block diagram, it would be better if you used the one which controlling the internal reference only and the other one tie it with the circuit ground, it might work). C2 here became a feed forward capacitor as the buffer is not an ideal current source/sink, it should be connected to the real ground in your circuit (and here it will add some delay as your cicuit is a current sense feedback). Another issue, the diode will provide his own feedback with a value related to the current flowing through it (non linear problem). Read about PID controllers....................... Here is my suggestion: Use instrumentation amplifier, "Inputs" on the sense resistor, its "Output" connected to "Vout_s"; and the gain of the Ins. Amp. can be adjusted for desired current output. And here you can use much lower sensor resistor value (suggested 1 to 100 mohm) :)
Good on, Ive found that you learn more by fails and play about trial and error.
when working for Ekco's in my distant past and working with the old lm741 op amps this was about 1980, you always had to have a cap in the feed back to stop osc.
Tantalum is your friend. At least, when it's not going thermite on you.
This is the problem with solderless breadboards in general. You're going to get capacitative coupling & lead inductance issues. For precision stuff, you need to go with a dead-bug or custom PCB prototype right from scratch.
Yes, totally agree! :)
I have had similar problems with discrete voltage regulators, in this case I think the breadboard is doing you no favours, you may also have issues with rf pickup. Good to see intelligent comments for a change.
There is no Problem with the datasheet application. You just did not built up the circuit which is in the data sheet. It says explicitly to use the LTC6655-2.5 but you used the LTC6655-1.2. They use 4.7 uF at Output, you use 10 uF. The scope thing is a bug for sure. Btw you should have a look on Graph 12 in data sheet. Plus I guess you crashed the IC by your original circuit which is catastrophic! However the worst mistake you made is that you simply forgot to connect pin 8 to ground.
I can see how it might be interpreted as a bug (the scope thing at 12:06), but if you think about it, its the firmware trying to replicate what would be seen on a CRT on the LCD. It appears to be looping to a buffer between LCD refreshes, so that when the LCD does refresh, it displays a better representation of what would have appeared on a CRT.
This time Dave didn't made a good enginerring work: 1) Noise and OSCILLATIONS (which is mostly what is happening in the circuits he has breadboarded) are not the same thing. 2) You cannot simply ignore the loop frequency response of the error amplifier inside the LTC chip before tweaking the reference design, 3) It is much easier to blame the IC than your own breadboard and test set-up, but definitely not the most professional approach.
*****
You are absolutely right on your comments and provide some common ground so that I now can also quite agree with you! Thanks for sharing your point of view.
Now i want to debug some blocks in my device, before making pcb, Thanks
And its actualy solderless boards problem, very noise
Dave, maybe try a cap on the "force" output and see what it changes apart from response time.
A capacitor (I would try10 UF Tantalum) from the op-amp (pin6) to ground may have fixed it. The data sheet says pin 4 must be connected to a noise-free ground plane.
Nice, but What about breadboard capacitance?
i love floating current regulators
Nowhere in the application note does it suggest using the the ground in this fashion, which may explain why it doesn't work. It would have been safer to build it as a precision reference and follow it with a current source.
When I started in R&D, I was told in no uncertain terms to never ever use one of those plug in things again. Design the thing and get pcbs made, then sort it out. Good advice, since its going to end up on a pcb, and the time you spend debugging a lash up is wasted.
I agree that this type breadboard may be a problem. There is parasitic capacitance caused by the pin to pin coupling between the bus bars. You can see the bus bars if you remove the paper covering on the bottom of the breadboard. Bar to bar coupling is likely enhanced (more capacitance) by the metal mounting plate that some breadboards sit on. This is bad for high frequency circuits. Although time consuming - hardwire the circuit on a bare copper PCB or make a PCB.
Esr of the output cap being a contributor to stability issues in linear regs ( same feedback loop stability issue here), a Tantalum cap rather than a poly may have been the way to go, just a bargain basement electrolytic has solved similar issues for me.
Great Videos Dave but i would have liked you to bring up more of your tutorials on different techniques or microcontroller environment or just the "fundamental friday" cause for us guys who are not Engineers in electronics but starting out enthusiasts it would be great help
I'm a long way from an expert but I'd have money on this sort of percision being very hard to achieve using a breadboard setup. Having this on a well designed and manufactured pcb would help significantly in my unqualified unasked for opinion.
The amplifier ground does not to have to be on the real ground? outside the diode path?
Lol, that damn thing would be better as a noise source! Geez!
Yep, Dave Jones is certainly a noise source!
My best guess on what could it be happening, is actualy the wires used to build the circuit on the protoboard,, they are long enough to behave as an antena, hence, inputing parasitic signals to a precission circuit like this, you will never find a precission refference built like this, you need a lot of shielding and higly conductive , short traces between components, this would be at least my guess,, i've had problems with this and it's almost imposible to get rid of some of that ripple, BTW love your videos Dave :)
When some oscillation is an issue my guess is that it is caused by parasitic inductances of the breadboard. I tried once making some boost converter from scratch (with no dedicated IC) and it just couldnt work, the efficiency was well below 50% and I couldnt pinpoint the issue untill I did the exact same circuit with the components I tried on a prototyping board and it works just perfectly with efficiency up to 90%. Turns out breadboard can be a real pain if you deal with high frequency ICs.
Waiting for the Nixie tube video :)
He has already got the tubes, Christmas mail bag.
I was always baffled Dave rarely talks about nixies.. I guess it's just one little electronic thing, but they have captivated the internet's electronics forums for quite some years now!
***** Well, you're right that vintage electronics appeals to young people. No need to use buzzwords like retro, or Maker. Jeez, does anyone outside of marketing even use those words XD? However, older visitors who get to see my nixie tube clocks also have no idea what it is and have never seen it before. AKA the obscurity of USSR technology can appeal to all ages.
I still think nixies are magic though.. The technology isn't that amazing, but the story that I can tell people is great. Soviet tech, production stopped in the late 70s early 80s, consume almost no power, resurrected from the grave by enthusiasts, found in old warehouses in eastblock countries.. etc. They have appeal, and I like it
I want that Analog Broadcasting equipment torn down, lolzz
hehe
I think you're going to find it completely boring. There's some neat stuff in there for sure, but most solid-state transmission systems are just a bunch of FETs and a combining backplane. Now if he got his hands on a tube rig, those are fun.
Alex Hartman lies! All lies! Its going to be crazy wicked science!
Haven't seen part 2 (yet), but at a guess: Too much gain introduced by the external transistor. That's why the darlington is even worse. Beta varies widely, so the particular 2N2222 might have very high beta/hfe. Use a lower gain transistor, or reduce the feedback proportion.
Control systems: Oscilliations almost always means gain is too high.
The problem could be exactly the no load configuration: It could well be, that when you put in the NPN-Transitor you have an configuration which requires an minimum load current. Look at one thing in the datasheet in particular:
"VOUT Force Pin. This pin sources _and sinks_ current to the load."
With the NPN Transistor in Series, the circuit can not sink any current, but the Error Amp will try to do so when VOUT Sense is to high ever so slightly.
But as an NPN Transistor is in Series, VOUT Force will go down without directly affecting the the sense voltage. Then the current of the VOUT Sense Pin (the sense pin is a voltage divider) will reduce VOUT Sense over time, till VOUT Sense is too low and then the error amp has to go back from a lower voltage back to a higher voltage.
Granted: If the sink capability of the voltage reference is the problem, the application circuit in the data sheet is a joke. One of the differences between a voltage regulator and voltage reference is the ability to source _and sink_ current. If that is a problem for an "typical application" then it is not an typical application for a voltage reference.
guess that's enough to provide current to leds or such that aint noise sensitive.
Good Stuff! Maybe lower out coupling Cap ESR will help? Newer products call for some pretty exotic stuff. Is it possible such HF noise could be caused by input damage by heat? Who knows.. Thanks for the vid!
How about a cap between the collector and base of the Darlington?
Love these videos!
And there i was eating up the reference designs from datasheets with a golden spoon thinking they came from the gods of electronics.
Seams quite straightforward to fix tho, just make your own error amp so that you can add in caps into it to slow it down so its stable, if done right it works well even on breadboards.
lesson enjoyably learned,
love the white beard I still have a long way to go with mine.
you just don't get these types of videos anymore on this channel..
Wow, that is exciting! My wife can't believe it. When the Martians come, we will definitely need this.
First off I'd like to say I've learned tons just by watching your videos Dave but I'm still a complete novice with this stuff .
Just out of curiosity, I see that there is a jumper between H12 & J11 connecting pins 3 & 4 of your LTC6655 but those pins are not defined on the datasheet. Is it possible that may be related to some of the oscillations you are seeing in the output of the module? Also, I noticed that the diode did not appear to be attached to anything. :)
Pins 3 and 4 are quite clearly defined at GND on the second page of the datasheet....
Can't you just whack on a huge value electrolytic capacitor on the force output, sense output, and output of the transistor? those MKP and ceramic/film caps ate low values, baybe larger values work better. Is it possible to reduce the internal gain of the feedback loop? maybe a voltage divider on it's sense?
Can you make the drawing/schematic any less readable?
I also have the Rigol Bug, even though i just recently bought it. Maybe we will get some firmware updates in the future :P
Hmmmm. Could you have a bad 6655? Nothing is perfect!!
ad8276 would be probably better to use and drive its REF pin
Any chances you can take a few minutes to share how large power inverter companies make keep the peak to peak whintin the voltage parameters? I'm trying to make my own power inverter, and don't know how to make sure I don't finish with a really large back emf feedback that will destroy all my equipment
Could the nastiness have come from MAKING the opamp fit the adapter? I ask because I have a few ATTiny85s that I bought the wrong sized DIP adapters for.
I just read the rest of k1mgy's comments. I agree.
any bug not documented is a feature.
"1R25" for 1.25 Ohms
Ones that got tired of trying to decide if dots in photocopies were decimal points or dust!
If it's a precision current source I assume you would need to account for the parasitics of the breadboard and just do air wiring like Bob Pease ? :)
COUNTERFEIT!...Mr. Chips. Ask me how I don't know. I've spent years over promising and under delivering. I know how to do it wrong. Cheers. Micro Image "We've Upped Our Quality, Now Up Yours". ❤
Can you put an opamp voltage follower in front of the voltage reference?
A Darlington? How about a Kelvington?
wow, thanks for that.
Might spend at least the Spanish subtitles?
grateful to you for having uploaded the video but I do not know the English language ...
por eso los españoles no tienen nivel de inglés, se esfuerzan más en traducirlo todo al español que en intentar aprender inglés
pero lo que veo ,mejor dicho lo que esta diciendo el tipo en el video no se puede traducir
There is no spoon, euh, sense output.
Breadboards suck... dead bug it up and try again. Add some decent local bypass for the input supply. Examine the datasheet for layout constraints.
Which Rigol is this? FW?
It seems like you have too much capacitance in the feedback loop. Since you are adding gain to your loop with the final transistor you want to be careful to not add any kind of delay I'm the feedback loop such as would result from stray capacitance. As was said in another comment it's likely coming from the breadboard itself. Sounds like an opportunity for dead bug and rats nest prototyping.
Wouldn't it be cheaper just to buy a 1amp plug like used on cell phones, etc.
Obviously you're missing the point of what Dave is trying to achieve.
A 1 Amp cell phone charger provides something between 4.5 V to 5.5 V
to charge something. The current will be whatever the phone or load will take upto 1 A, so The current can be 0 A to 1 A. Such a charger behaves as a voltage source.
Dave tries to make something that will deliver 1.000 A as precisely as possible independant of the voltage (within practical limits of course). This is called a current source. It is intended for electronic measurements, not charging your phone.
Uh ok, whatever. Some of these home made kits are ridiculous because you can already order the boards or go to rat shack and get one. Maybe if you are using a Raspberry Pi on your car multimedia head unit like bored1980 does and you need more power to run more then 2 usb devices with it.
7:53 lel, you're getting trolled with the mailbag nowadays?
Just ooowfoool..
Nice video Thumbs up on this one. Thanks
It was posted 1 minute ago, you haven't even watched it yet!
I fudged a little mate. Sorry. Thumbs up still.
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Ivan Eduardo Veloz Guerrero
no.
Rubus Roo ?
nice videos you have there! ..if you get an ascillator somewhere you don't want .. you need to cut or reduce the feedback or reduce the amplification .. or maybe add some delay or phase shift to stop it .. the next old video seems to know how to make an oscillator (LC) .. to stop that you do the reverse! .. or remove some C which makes it to oscillate!;) --> ua-cam.com/video/a8casNPDvI4/v-deo.html
funny that in USA the current flows reverse direction compared to the situation here in Europe .. I don't know how the situation is in Australia? Here the current always flows from the positive voltage to the negative pole (and the electrons flow reversed) .. at least in old US videos it seems to be a common "local" fact that electrons and current flows the same direction (from - to +) .. very strange? haha!:)
Try putting a RC filter to the OP amp output ... you might also put some resistor to the op amp input to protect it and why not some RC also??
I still wonder how a b***h oscillates.... Master? :)
+t33th4n You know.. back and forth until you get tired of it!
A sayries doyode fixes ayverything! Ya just the way it sounds....
What am I missing? You completely changed the circuit, used a created gnd from an op-amp output, then claimed that the application note was faulty. You made two grave errors. One- you think that an op-amp output is the same impedance as the GND in the circuit, and 2, when you plugged in the darlington you changed the loop gain which is part of the stability of the amp. I don't think the breadboard is the problem.
To claim that the application note circuit doesn't work, you should actually test the application note circuit. In this case you are testing your assumptions and claiming that the application note was faulty. Sorry, I love your videos except not this one.
Did you actually watch the video? Dave removed his mods and ran the circuit as per the app note, same result.
Oops, I did watch it, but now I re-watched it because of your question. Thank you, I don't think I noticed that part where he repeated the original circuit the first time through.
However, I am not sure he really did correctly recreate the app-note circuit. He claimed to have re-run it, but I don't see C2, the 4.7uF cap in his "repeating original" circuit at 9:38 in the video. Just because he said that it shouldn't need caps NEAR the circuit and he wanted to test it that way, is he using the cap that is still hooked up to the other circuit? The other circuit still looks powered. And if he did duplicate it, but failed to put the two caps close to the circuit, why did not not then put them close and duplicate the test? I think he just plain forgot or did not include C2 thinking that it was just some noise reducing component. Claiming that the app note circuit does not work is somewhat serious and I have made tech support complaints when I found what are essentially flaws in the data sheets. Any decent company will act on a data sheet error. But, you have to make a good attempt at documenting the problem first.
It is true that App note circuits don't always work, but I have a lot more faith in LT app note circuits than TI app note circuits for example.
Linear tech chips are not very good, every circuit I have tried from them either dont work or dont meet their spec. I no longer use their parts.
FIRST ! lol awesome video man !