5.333 volt - Page 1
Forum section: electronics / projects

author: JanJansen
author_rank: Frequent Contributor
timestamp: July 07, 2017, 01:26:15 pm
content: What is the best and cleanest way to get 5.333 volt with multiturn trimmer ?I need to have exact 5.333 volt for building a TB303 synthesizer :http://privat.bahnhof.se/wb447909/dinsync/service_manuals/TB-303.pdf

author: ajb
author_rank: Super Contributor
timestamp: July 07, 2017, 02:13:15 pm
content: Connect one side of the trimmer to >5.333V and the other side to <5.333V, and tweak it to suit? Not sure what you're really asking for, here. Maybe follow it with a unity-gain buffer if you need a lower impedance? Or use a precision reference?

author: alm
author_rank: Super Contributor
timestamp: July 07, 2017, 02:23:39 pm
content: If it is supposed to be a power rail, then an adjustable three terminal regulator like the LM317 would be the easiest solution. Feed it with something like 9 VDC.But how about some proper requirements. Available supply voltages? Min and max current draw? Allowed noise? Budget? Volume?

author: JanJansen
author_rank: Frequent Contributor
timestamp: July 07, 2017, 02:47:25 pm
content: It has 12v supply voltage, current draw i,m not sure.I only make 1 or 2, what are the options ?With the LM317 you have a resistor to ground, i dont want that to influence the schematic for the synth.

author: alm
author_rank: Super Contributor
timestamp: July 07, 2017, 03:44:43 pm
content: Fine, then build the schematic from the synthesizer. It includes a power supply that creates 6 V, 5.333 V and 12 V rails from a 9 VDC input.

author: technix
author_rank: Super Contributor
timestamp: July 07, 2017, 04:30:16 pm
content: You can match a 7805 regulator chip and a 1N5819 Schottky diode to give you the 5.333V. If properly matched the voltage drop of the Schottky diode will push the output voltage to 5.333V. Or from some less than reliabel brand (loose tolerances) you may even find 7805 chips with 5.333V output voltage.

author: JanJansen
author_rank: Frequent Contributor
timestamp: July 07, 2017, 05:56:36 pm
content: Thats funny, buy a 5v regulator and hope for 5.333.I,m not sure how to connect the Schottky diode.

author: JanJansen
author_rank: Frequent Contributor
timestamp: July 07, 2017, 06:03:30 pm
content: I saw a : dont try this at home movie before,someone hooked up a 7805, with a resistor to the ground, then it gives higher voltage.

author: Zero999
author_rank: Super Contributor
timestamp: July 07, 2017, 06:25:21 pm
content: How accurate does it need to be?The TL431BC is 0.5% accurate and 0.5% tolerance resistors aren't that expensive.http://www.homemade-circuits.com/2012/12/explaining-programmable-shunt-regulator.htmlFor VO= 5.333V0.5% valuesR1 = 1k82R2 = 1k61% valuesR1 = 1k87R2 = 1k65You could also replace either R1 or R2 with a slightly lower value, in series with a trimmer, but beware the drift of a trimmer will be higher than a precision resistor.

author: JanJansen
author_rank: Frequent Contributor
timestamp: July 07, 2017, 07:12:53 pm
content: It has to be exact 5.333 volt measured.

author: PA0PBZ
author_rank: Super Contributor
timestamp: July 07, 2017, 07:17:48 pm
content: Quote from: JanJansen on July 07, 2017, 07:12:53 pmExact doesn't exist and if it did you couldn't measure it.So 10%, 1%, 0.1%?And what is the accuracy of the DVM you are going to use to measure it?

author: Zero999
author_rank: Super Contributor
timestamp: July 07, 2017, 08:58:13 pm
content: Yes, there's always a limit to precision. Nothing is completely accurate.Another problem is drift. You might be able to trim to +/-0.001% which would be between 5.33294667V and 5.33305333V, it won't necessarily stay there. It may drift considerably over time, especially as the temperature changes.

author: DBecker
author_rank: Frequent Contributor
timestamp: July 07, 2017, 09:58:23 pm
content: The original schematic (page 5 ref 25D) shows a 1sz46a zener creating a 6.2V reference, and then a resistor devider tweaked with a trimmer for creating a 5.333V level, with an opamp voltage follower creating the supply.The service manual probably tells you to adjust to 5.333V at "operating temperature". But it's pretty certain that it will drift significantly with changes in conditions and over time. My guess is that you don't need the accuracy suggested. They really mean "adjust to 5 1/3 V" and do a pretty good job, just like the 1V and 4V level are described as 1.000V and 4.000V

author: sokoloff
author_rank: Super Contributor
timestamp: July 07, 2017, 10:00:39 pm
content: Between 5V and 6V; slightly closer to 5V; use your open eye.

author: Crumble
author_rank: Regular Contributor
timestamp: July 07, 2017, 10:23:27 pm
content: I checked the schematic and it uses an 1SZ46A reference diode which is not accurate, but has a very low temperature drift. You will find the datasheethere. It is tweaked with a pot in the schematic, so if it says 5,333V, please tweak it with a 4 digit multimeter to 5,333, but do search for a 50ppm/C reference, because thats the spec on the 1SZ46A. It does not seem to be available, but you might use anLM329. It has a slightly higher temperature coefficient of 100ppm. The opamp (theAN6562) does not seem to be particularly temperature independent or low offset, but it does not have a major effect on the temperature drift of its output.

author: JanJansen
author_rank: Frequent Contributor
timestamp: July 08, 2017, 01:52:56 pm
content: Thanks for the reply`s,how many milliamps does it need for this schematic you think ?Maybe i will just use 1 opamp and voltage divider, why zener ?sorry i,m more beginnerbtw : i still need to buy a multimeter that can measure this, for now i can set it to 5,33 volt.Maybe i will a 6v regulator + a 5v regulator, then use the presision trimmer in between ?

author: Crumble
author_rank: Regular Contributor
timestamp: July 08, 2017, 03:32:43 pm
content: The zener requires only 1mA to work, and the LM329 works down to 0,6mA. I do not know how critical the voltage level on the syth is, it is quite difficult to tell how it works without the service manual. A synth will likely drift out of tune when something with poor stability would be used and I think the voltage will have to be tuned for a specific sound rather than voltage.Creating the 5,333V from the 6V supply with a voltage divider would require an equally stable 6V supply, which this is not, because it seems to be fed from batteries that have a voltage that is dependent on quite a lot of circumstances, including their state of charge.I still don't know what you're trying to do here. Do you have a synth of this type you are trying to repair, or are you trying to build a new one from scratch with the schematic? Given the specific part that was used, the designer seems to have gone for stability, else a cheaper part would have done. Please let us know what your intentions are, maybe with pictures and links to show what problems you are trying to solve.

author: JanJansen
author_rank: Frequent Contributor
timestamp: July 08, 2017, 04:12:18 pm
content: Hi, i wanto create it from scratch.I have many things todo, so i just sorting things out in advance.I,m realy new to VCO stuff, no drift is realy important, i also did not solve on what to use instead of the 560 ohm tempco resistor.Its hard to create a clone if parts are not available anymore, cloning the tr808 drummachine wil be easyer then this tb303.

author: amyk
author_rank: Super Contributor
timestamp: July 08, 2017, 04:25:45 pm
content: What exactly does it need 5.333V for (and why wouldn't, e.g. 5V or 6V be adequate)?The TB303 has a custom microcontroller. That will probably be the biggest obstacle to cloning one.

author: technix
author_rank: Super Contributor
timestamp: July 08, 2017, 04:37:54 pm
content: Quote from: JanJansen on July 07, 2017, 05:56:36 pmIn one of my designs I needed a 5.25V +/- 5% rail. I put a 1N5819 in series with the feedback pin of the LM2596-5.0 fixed voltage switch mode buck converter chip and got the 5.2V that way.For 7805, connect the GND pin of the 7805 to the anode of the Schottky diode, and ground the cathode of the diode. This way the diode shifts the reference voltage of the regulator chip up with its voltage drop. This configuration can have bad line and load regulation due to the diode being present on the ground instead of the feedback pin. For (mostly switch mode) regulators that have a separate feedback pin put the diode there to create a voltage drop in the feedback loop.

author: mikerj
author_rank: Super Contributor
timestamp: July 08, 2017, 04:43:33 pm
content: Quote from: Crumble on July 07, 2017, 10:23:27 pmAn LM431 (precision TL431) has 50ppm tempco, seems a good fit for this.

author: Crumble
author_rank: Regular Contributor
timestamp: July 08, 2017, 05:31:49 pm
content: Quote from: JanJansen on July 08, 2017, 04:12:18 pmGood luck with that! I like your enthousiasm, but I won't be able to help you with that... I also don't think the 5,333V is going to be your biggest problem.

author: DBecker
author_rank: Frequent Contributor
timestamp: July 08, 2017, 06:11:20 pm
content: Looking at the schematic, this supply is the only tightly regulated one. It serves as the supply voltage for several critical sections, notably the 7174 flip-flop. The flip-flop outputs feed the precision resistor network made of R74-R90. At a glance, that appears to be acting as a DAC, which suggests that stability and noise rejection is more important than the exact value.Edit: Oh, the block diagram labels this as the D/A converter.I would substitute an adjustable LDO regulator with a high PSRR. You might as well get precision resistors to set the voltage, since they will cost barely when buying small quantities. Or you can modernize the whole section and go with an integrated DAC.

author: dmills
author_rank: Super Contributor
timestamp: July 08, 2017, 06:46:09 pm
content: The trap here is that the thing (like most analogue synths) uses 1V per octave for the control voltage, so that voltage is probably fairly critical to making the whole thing stay in tune, including from one octave to the next), but that said, it was a rather simple low cost consumer oriented design and the things always did drift like a pig.Pick a modern bandgap reference, divide with 0.1% low tempco resistors, buffer with an opamp, I bet you can get close enough without any real need to trim this.The micro will be a problem, but it is nothing that a modern part combined with a decent programmer could not sort out (Together with adding useful things like USB Pattern load and save and maybe MIDI).regards, Dan.

author: DBecker
author_rank: Frequent Contributor
timestamp: July 08, 2017, 07:46:19 pm
content: Quote from: dmills on July 08, 2017, 06:46:09 pmAhhh, that's the piece I was overlooking. I thought that the DAC was directly generating a waveform. Instead it's generating a voltage, which is fed into a VCO to generate the tone. I now see why the reference voltage is important for tuning.It's even more critical that the DAC resistors are matched, or the synthesizer won't generate an equal tempered scale (a correctly tuned 'A' will result in other notes being off-frequency).

author: WZOLL
author_rank: Regular Contributor
timestamp: July 09, 2017, 03:37:21 am
content: What about the x0xbox? Its a kit 303 with a large community. You can buy pcbs, panels, and a micro fromhttps://willzyx.com/index.phpand it will probably be cheaper and easier than making one from scratch unless you like the extra challenge. I feel your pain as I'm currently building an entire Moog modular from scratch based on the service manual and a few forum posts.

author: JanJansen
author_rank: Frequent Contributor
timestamp: July 09, 2017, 01:51:00 pm
content: Thanks for all the reply`s,yes the DAC has 0.1% resistors ( expensive ), and is critical to drive the VCO, the VCO has the 560 ohm tempco @ 3300ppm, maybe i try replace it with a regular 1% film resistor ?Indeed, the voltage is for the 1 volt per octave VCO, the flipflops are used to buffer the pin outputs to have 5.333v and usable impedance.The microcontroller is no problem for me, i build it without the sequencer, with MIDI instead.For a DAC instead of resistors and flipflop would be nice, then i still have the problem that its 5 volt, + extra parts needed, since the PIC internal DAC is not perfect linear.5 volt is not enough to get the whole range for all notes used, i dont know what will happen on 6 volt, that is a nice one to try.I will also look at parts suggested, thanks.Quote from: Crumble on July 08, 2017, 05:31:49 pmI,m also cutting corners a bit at some parts, make the VCO as good as it gets, its not a super big project, only difficult because its new for me, it will make some sound in the end.Quote from: WZOLL on July 09, 2017, 03:37:21 amI also use theyr schematics, because the original has mistakes drawn.Quote from: WZOLL on July 09, 2017, 03:37:21 amNice one, same reason, no money for a xoxbox.I also build extended midi implementation, in the end completly MIDI adjustable for all parameters, first lets see if this VCO works in this build.I will be alot cheaper then when i buy anything labeled xoxbox.

author: PA4TIM
author_rank: Super Contributor
timestamp: July 09, 2017, 03:18:30 pm
content: Quote from: JanJansen on July 08, 2017, 01:52:56 pmI have designed and build a RF generator with VCO's. I used a LT1027 Vref for that. If things need to be so precise it will not be the only part that needs to be precise. But sometimes even more important is stability. Most often for temperature. A 104 ohm resistor with a tempco of zero that you trim with a high value low tempco parallel resistor is better as a 0,1 % resistor that drifts all over the place. You can often work around things. For instance place things in an oven. A component with a medium tempco in an oven will not drift as long as temperature does not drift. Placed on a temperature stable location can make it usable. But if you mount it next to a heatsink from something that dissipates sometimes a lot and sometimes nothing, it will give problems.About the meter. A meter that will be accurate to 1mV for 5,333V must be a 60.000 count meter. Or a 200.000 count meter. You need at least 1 digit more and the tolerance must be low enough to keep the total tolerance within the last digit. (So 0,0000001% plus/min 15 counts will not do) And to be really sure it must be calibrated. It must be stable over time and temperature.Such a meter is expensive. A not expensive meter that can be usable is the Brymen BM-869s for instance. It is 50.000 count but has a 500.000 count mode but in theory it is not good enoughBut you better sit down before you look up the price of meters that 100% fit your demands.

author: amyk
author_rank: Super Contributor
timestamp: July 09, 2017, 03:39:48 pm
content: A frequency counter may be a better choice, since now that you mention the voltage is to control the frequency, and that's what you ultimately want to control the accuracy of. Depending on the tolerances on the other components, getting 5.3330000000V exactly might not give you the right frequency anyway.

author: JanJansen
author_rank: Frequent Contributor
timestamp: July 09, 2017, 03:42:05 pm
content: I,m going for the HMC 8012 @ €850 incl tax.https://www.eevblog.com/forum/testgear/hmc-8012/msg1247032/#msg1247032https://www.rohde-schwarz.com/us/product/hmc8012-productstartpage_63493-44315.htmlHow it is calibrated i cannot test, hope its good.

author: JanJansen
author_rank: Frequent Contributor
timestamp: July 09, 2017, 03:45:07 pm
content: Quote from: amyk on July 09, 2017, 03:39:48 pmI was also thinking for sometime to build in a frequency counter chip, maybe autotune will be possible also, let the synth tune itself.

author: Crumble
author_rank: Regular Contributor
timestamp: July 09, 2017, 09:58:36 pm
content: Quote from: amyk on July 09, 2017, 03:39:48 pmWell said. I agree the actual voltage is likely tweaked differently. It might be easier to try and find a service manual for this synth and check how it is calibrated. It likely needs an accurate frequency reference rather than a voltage standard.Quote from: JanJansen on July 09, 2017, 03:42:05 pmAre you seriously going to buy a €850 meter and hope for the best? Looks like a bit of overkill. Try a simple 4.5 or so digit meter first, this might be a better idea. Usually the meters that specify the accuracy in "% + x digits" for every range are the ones to be taken seriously (this one has it in % of reading + % of range, which is basically the same). Given the fact the design uses a potentiometer to set the voltage the stability isn't going to be stellar anyway.

author: rstofer
author_rank: Super Contributor
timestamp: July 09, 2017, 10:33:02 pm
content: Quote from: Crumble on July 09, 2017, 09:58:36 pmAre you seriously going to buy a €850 meter and hope for the best? Looks like a bit of overkill. Try a simple 4.5 or so digit meter first, this might be a better idea. Usually the meters that specify the accuracy in "% + x digits" for every range are the ones to be taken seriously (this one has it in % of reading + % of range, which is basically the same). Given the fact the design uses a potentiometer to set the voltage the stability isn't going to be stellar anyway.I sure hope I don't screw up the math...Suppose the goal is to get 5.333V +- 0.0001V so 5.3329..5.3331V. The way I see it is we need 0.002% accuracy because 0.002% * 5.333V = 0.0001V This is going to require a very costly meter!Now, if 5.333 +- 0.0005V (5.3325..5.3335V) is close enough then 0.01% accuracy is good enough but even that isn't easy to get!The HMC8012 doesn't come close to meeting the second requirement. It seems to me that the total accuracy is 0.02% + 40 * 0.002% or 0.1%. The '40' comes about because the second term is a percentage of full scale and we would have to use the 40V scale.The 6-1/2 digit Siglent SDM3065X is good for 0.012% so it's just about right.http://www.siglentamerica.com/USA_website_2014/Documents/DataSheet/SDM3065X_DataSheet.pdfThe thing about DMMs is they have a whole lot of digits but some are useless because they are swamped by the accuracy specification.ETA:The SDM3065X is cheaper than the HMC8012 so it would be worthwhile to create a spreadsheet comparing features and accuracy.

author: JanJansen
author_rank: Frequent Contributor
timestamp: July 10, 2017, 02:35:17 pm
content: So the HMC 8012 is not good enough ?, not good for my head all that math.Anyways : no Siglent for me Rstofer, i explained in my topic :https://www.eevblog.com/forum/testgear/hmc-8012/msg1247032/#msg1247032Ok, its €20 cheaper for 6.5 digits, its also new, maybe i will wait until R&S/Hameg release a new DMM with better specs.the HMC 8012 is older then the Siglent, i dont know if they will release a DMM this year ?there was a picotest also, half the price for 6,5 digits :http://www.eleshop.nl/picotest-m3150a-multimeters.html

author: PA4TIM
author_rank: Super Contributor
timestamp: July 10, 2017, 03:12:55 pm
content: My favourite and best 6,5 digit meter is the Keithley 2000, I bought it new about 7 years ago, it and it is very stable and lineair. Not a modern fancy look but just a very good meter.As far as I now understand the VCO needs to be at an excact frequency and that is when the set-voltage is 5,333. If so, better use a counter and make the voltage as stable as possible.But how well is the VCO spec'd, I asume that also has a tolerance. So if you buy 50 are they all at excact the same frequency if you use 5,333V ?A VCO can be used to make a stable frequency that you can control with a voltage f.i. to auto-adjust it.But a VCO also can be used as a variable oscillator, I do that in a (sweep)generator.The latter needs a stable voltage with a wide span like 1 to 10V or so in 1 turn of a potmeter, the first needs a stable and precise set voltage (if you do not use a counter) that you can set with a high resolution, f.i. 5,3 to 5,4V in 10 turns of a multiturn pot.If you live nearby you are welcome to check your meter so you know the reading it must have at exact 5,333V or adjust the VCO at a precise frequency. (I do not do complete calibrations, that is a lot of work, but checking a few DC voltages in the 10V range is no problem)

author: Crumble
author_rank: Regular Contributor
timestamp: July 10, 2017, 03:22:09 pm
content: Quote from: JanJansen on July 09, 2017, 01:51:00 pmGiven this quote, how much effort are you going to put into finding a meter that can reach 5,333V exactly? Set the voltage to 5,33V with your existing meter first. Nothing will blow up if its out by a few mV. It might be slightly out of tune, but hey, it will also be out of tune if you're cutting corners in the VCO already.I think the offer of PA4TIM is quite a good one, access to accurate instruments does not always come easy. I must say that given the fact your head hurts after some simple arithmetic you might not have the proficiency in building a good synth from scratch. If you have the money to spend, please invest in good equipment, it will last you a good long time. This alone though will not make building a complex device particularly easy. And (again) look for the service manual for this equipment, it will show you what you need to tune on it. Usually it will show you a sequence of steps, alternating between measurements and adjustments until an end result with a specific accuracy is reached.

author: JanJansen
author_rank: Frequent Contributor
timestamp: July 10, 2017, 03:39:34 pm
content: Thanks for the offer PA4TIM, i live far north, to far usually.@ Crumble, your right, i could use my current meter to measure 5.33v.I also need to match transistors to 2mv hfe, and measure rms for some other project.My multimeter floats around for such values.

author: rstofer
author_rank: Super Contributor
timestamp: July 10, 2017, 04:00:03 pm
content: Quote from: JanJansen on July 10, 2017, 02:35:17 pmI don't have an opinion on what you should or shouldn't buy, I just picked a meter thatshouldbe capable. All I wanted to do is cause you to think a little bit about what you're trying to measure and whether certain meters, in the worst case for accuracy, could make the measurement.You would think a 5-1/2 digit meter would be adequate, and it could be, but the devil is in the accuracy specifications.

author: Crumble
author_rank: Regular Contributor
timestamp: July 10, 2017, 04:31:48 pm
content: Quote from: JanJansen on July 10, 2017, 03:39:34 pmOk, that's easy. To match transistors you don't need your meter to be accurate, it's just for comparison. A very basic meter would do. For RMS frequency it's important most meters only show accurate RMS values up to the 100s Hz. It is as rstofer says: the devil is in the details/specs.

author: WZOLL
author_rank: Regular Contributor
timestamp: July 11, 2017, 01:59:29 am
content: Quote from: JanJansen on July 10, 2017, 03:39:34 pmThere is supposed to be a 10k resistor between the two transistors on the PNP tester like the NPN version but i don't think it matters too much.

author: 2N3055
author_rank: Super Contributor
timestamp: July 11, 2017, 08:22:32 am
content: People cannot hear less that a one hundredt (1/100), cent, of a tone pitch.. 0.1% of tone pitch is plenty accurate...TL431 is plenty accurate and temp stable..If you want to go crazy, LM399 with a opamp buffer will make it very stable.You set it up approx 5.3 V with a voltmeter you have , and then connect a tuner to the synthesyzer and fine tune the tone pitch...

author: KL27x
author_rank: Super Contributor
timestamp: July 11, 2017, 11:23:36 am
content: QuoteI don't think this would work. Are you sure there wasn't a second resistor? You might call it R1 and R2. R1 between the output and the ground pin. And R2 between the ground pin and the ground. And if you renamed the ground pin as the "adjust pin," whadya know? This is a perfectly fine way to change the output of a linear voltage regulator. The output would be 5V * [1+(R2/R1)]. This is exactly how you set the output of an "adjustable" linear voltage regulator or the gain of a non-inverting opamp.The only major drawback is that the heatsink can't be in contact with ground, anymore. If you set an LM7805 for 5.333V, the heatsink will be referenced to 0.333V.

author: Crumble
author_rank: Regular Contributor
timestamp: July 11, 2017, 02:40:16 pm
content: And let's not get carried away here. The part that is in the current design has especially low drift. When using a LM317-like device when loaded only very lightly you might get a moderate drift, but is less than ideal. Using a 5V regulator you're just asking for trouble, because it was not designed to be used floating. It will likely drift with temperature and/or loading of the exit.

author: DBecker
author_rank: Frequent Contributor
timestamp: July 11, 2017, 08:10:55 pm
content: Quote from: 2N3055 on July 11, 2017, 08:22:32 amDesign for temperature/environmental stability first. Once you have temperature stability, simply tune it. The output frequency is what you ultimately care about, so tune it using a frequency counter or even a guitar tuner rather than a $$$ voltmeter.Note that you have two parameters -- a slope and baseline. The VCO is nominally 1.000V/octave (?) and the DAC step is set by the 5.333V reference. If the VCO isn't actually 1.00000V/octave, there isn't a point in setting the reference to 5.333000VEchoing some of the details:1V per octave12 steps per octave (a modern equal tempered scale)6 bit DAC at 5.333VTune at 2.75V to 110Hz / note A2 (middle C is 'C4' at about 262Hz)0 => 0.000V12 1.000V C124 2.000V 65.4Hz C233 2.750V 110Hz A236 3.000V 130.81Hz C348 4.000V C460 5.000V C563 5.250VThe reason for tuning at 2.75V to 110Hz / A2 puts is that it is almost at the midpoint of the DAC, You could do better tuning at a count of 32, but that's not a note.

author: KL27x
author_rank: Super Contributor
timestamp: July 12, 2017, 12:13:54 am
content: QuoteIt is not floating. It is referenced to ground, same as it is when you attach the "ground pin" to ground, directly. The ground pin on a linear regulator like 7805 is not a supply pin. It's a reference pin. Think of it as an input of an opamp. If you want to dissect the power supply of the regulator, itself, Vin is the supply and Vout is the ground.As long as you select the right resistances and in/out capacitors, there is no reason this will drift with temp or loading or oscillate anymore or less than a 7805 or lm317 or 90% of linear regulators on the market... although there are surely better, more complex precision linear regulators for any given task with better balancing of thermal coefficients and whatnot. As for loading, it will maintain the 5.33V output until it overheats, just same as it ever would... which would be based on the power dissipation from (Vin-Vout) x current.The problem with using fixed regulator and adjusting it is that you can't adjust it lower than the original rating. And the heatsink will be at a strange voltage. You can think of an adjustable linear regulator as a fixed 1.24v to 1.25V regulator with heatsink on the output (perhaps using P instead of N, or vice versa).

author: technix
author_rank: Super Contributor
timestamp: July 12, 2017, 12:39:13 am
content: You can also try the assisted Zener circuit, with matched 4.7V Zener and NPN transistor that emits 5.333V.

author: Crumble
author_rank: Regular Contributor
timestamp: July 13, 2017, 11:32:20 pm
content: Quote from: KL27x on July 12, 2017, 12:13:54 amAre you sure? In case of the LM317 I would certainly agree with you, it is also quite visible in the block diagram inits datasheeton page 8 (the old datasheet actually showed the transistors, but I can't find one right now). There is only a few µA of current out of the adjust pin, which change little and, in absolute numbers, very little spread. Its internal bias currents are from Uinto Uout, and they therefore require a minimum load. If you check thedatasheet of the µA78xxyou will find the internal opamp have been constructed with the bias current running from Uinto Gnd, and are between 4,2 and 8mA (so hardly practially specced with a huge range between typical and maximal alone, and no minimal figure), with a specified sensitivity to Uin(1,3mA over the range) and Iout(0,5mA over the range). You will need quite a low resistance resistor divider network to make this work well and would make this type of regulator essentially useless for floating applications that require any immunity from Uin, Ioutor temperature (the effect of which on bias current is unspecified). Another giveaway is that it can work without a load on it without floating up significantly, and its dropout is slightly lower at 2V instead of 3V. Therefore the 7800 series also comes in loads of voltage versions, so you can select the proper one for the job, and the LM317 only comes in one type, the one with the 1,25V bandgap reference, which is in itself quite an impractical voltage to use, but lends itself well to the resistor divider system.I must admit I used the phrase '5V regulator', which was rather vague, but I have yet to encounter a 5V regulator of any type that behaves significantly different in this respect than the 7805. The idea of using a 7800 series device is practicable (even as a floating configuration) in a lot of situations, but it is obvious the syth we are talking about now needs something that is especially insensitive to temperature. This will require a specified sensitivity to temperature of the relevant currents. It will also make using a Zener diode or a transistor junction impractical, because those drift with temperature too (with zeners there is a sweet spot somewhere at about 6V where (I believe) opposing effects cancel and the drift is minimal, this is visible on page 5 of theBZX79C zener series datasheet)

author: KL27x
author_rank: Super Contributor
timestamp: July 14, 2017, 05:59:21 am
content: Regarding the bandgap reference and minimum loading, that is a good pickup on the different path. But in practice it works. And the resistor network does not have to be very low impedance. Forget OP requirement and needs for the part in synthesizer. I was commenting in regards to earlier comments about putting a diode or a single resistor on the ground pin of a 7805 to raise the voltage. Diode is going to be much less heat stable and blind luck to get exact voltage. Single resistor I don't see how that works, at all. Using feedback resistor and voltage divider, it works very well.

author: KL27x
author_rank: Super Contributor
timestamp: July 14, 2017, 08:44:57 am
content: BTW, just because engineer specifically design/optimize and marketer specifically advertise things, it doesn't mean it won't work another way.I have never seen an lm317 give wrong voltage due to minimum load. I have ever tested the output voltage with just the load of a DMM volt meter. I dunno what the oscillation is or isn't. But the voltage always tests fine with no load. Or perhaps the problem is that an oscillation can develop with a below threshold load which varies just so?https://www.eevblog.com/forum/beginners/lm317-getting-proper-voltage/When I read that, I thought he either didn't have as much input voltage as he thought, or he did something wrong. But it never fails someone brings up minimum load on the 317, tolerances, any other gotcha that is printed somewhere in a datasheet.

author: alm
author_rank: Super Contributor
timestamp: July 14, 2017, 09:11:26 am
content: Quote from: KL27x on July 14, 2017, 08:44:57 amThat is true. It will also likely not die the second you exceed the absolute maximum input voltage. Or oscillate if you leave out all caps. But only relying on guaranteed specs makes it less likely for a design to break when you switch manufacturer or the manufacturer switches process, or tolerances conspire against you. That is good engineering. Of course you can do your own characterization, but that would require extensive testing over input voltage range, temperature and whatever may be important. That is a lot more work than just calculating your circuit for worst case datasheet values. How much resources are you saving by exceeding guaranteed limits?Quote from: KL27x on July 14, 2017, 08:44:57 amThe manufacturers continue to print the misleading sample circuit with an LM117, despite the LM117 having been removed from the datasheet because they discontinued it. So it is an easy mistake to make. And troubleshooting is about excluding things that are easy to test first, and replacing resistors is one of the easiest tests you can do.

author: KL27x
author_rank: Super Contributor
timestamp: July 14, 2017, 09:24:06 am
content: There is no one going to design a product doing what I just described. This does not improve the circuit (it has drawbacks I already mentioned in addition to what crumble pointed out). There are already products that are just as cheap.But if you have an lm7805 in your hand and you want it to output 10 or 20V, you can do it the right way, and it will work, and it is not a hack. It is using a (integrated) circuit as a tool to achieve what you want.Max input voltage of an lm317 is stated in the datasheet as 35V. Tim has used them at over 100V. If you understand how it works you can sometimes do things with circuits that aren't covered in the datasheet.Regarding lm317 minimum output, I don't care which manufacturer you use. If your input voltage is static, the output load is static, the output voltage is going to be correct, even with below minimum load.

author: Crumble
author_rank: Regular Contributor
timestamp: July 14, 2017, 11:08:40 am
content: Quote from: KL27x on July 14, 2017, 05:59:21 amWhat do you mean by that?QuoteThat I'm sure it will, it does work, but we are treading on unspecified ground now, and this is often ill-advised, especially when no thorough knowledge exists of how and why it works (which, quite frankly, seems to be the case here).QuoteIt will when you want the voltage to be exact and stable. You will, for example, need an equivalent resistance (R1//R2) of 25 Ohms to force a regulator with a 4mA spread in bias current to stay within 100mV. If you use more, the output voltage will be way more dependent on the bias current. I have now assumed a 4mA spread, but the minimum was not specified, so the actual spread is likely to be larger. To be fair, with just a 0,333V bump needed this is only a minor issue, requiring about a 400/25 Ohm divider to get it right (exact figures are slightly more difficult to calculate, but these can be).QuoteOk, that was not completely obvious to me, sorry about that!Diode is going to be much less heat stable and blind luck to get exact voltage. Single resistor I don't see how that works, at all. Using feedback resistor and voltage divider, it works very well.The single resistor is quite simple, but as you said yourself: "But in practice, it works." I would like to add it is actually quite simple. The (relatively stable) bias current flows out of the Gnd pin, and will cause a voltage drop over the resistor. As said, the bias current has a wide and incompletely specified range, but is likely to be rather stable and can be tweaked to a specific regulator. The resistor does amplify the changes in bias currents, so using this for high voltage "bumps" would be ill advised.Quote from: alm on July 14, 2017, 09:11:26 amWell, I think it will die (slightly) over max voltage. Maximum voltage specs are a usually quite a hard limit of the transistor geometry. It will cause depletion areas of the transistor to hit the next area of doping, introducing new charge carriers from other parts of the IC, essentially causing the junction that is supposed to be isolating to conduct, with often catastophic consequences. The failure mode of overvoltage is not always a simple one, but never ever rely on having any time at all when overvolting any piece of silicon. Oscillation will occur in LM337s, but LM317 are specified to be able to run without output capacitor. Input capacitors are required as soon as the inductance of the feed wire starts getting an issue. This happens remarkably quickly, especially at high currents. It is capable of very high frequency oscillations (into the low 100s of kHz), even when moderately loaded.The marketing argument might work for consumer applications, but most silicon is specifically designed for industrial use and the specs are often quite reliable and complete. I must admit there are a few quirks still present, like always characterising the maximum power as the one you can dissipate at TC=25°C, which is quite inplausible to actually achieve. It does give you a metric to compare it with other manufacturers.Quote from: alm on July 14, 2017, 09:11:26 amIf I remember correctly the only difference between the LM117 and the LM317 is its temperature range and accuracy figures, for most means and purposes they are the same. I believe it was a military spec unit and cost quite a bit more too. There might not have been a sufficiently large market for it. The army might be switching to switchmode too...Quote from: KL27x on July 14, 2017, 09:24:06 amSo you're saying nobody is going to design that way, but you can still do it won't be wrong doing so? Sounds contradictory to me... Additionally, if you have a 5V regulator the issue with voltage variations will be quite some larger when you want a significant voltage bump like up to 20V. Please do your calculations, what kind of a resistor divider will you need if a 1mA variation in bias current will only yield a 16mV change in output voltage (please note the 1mA is the specified change in bias current as specified for the µA7805 and the 16mV is the voltage regulation of an LM317 as specified at 0,04%/V line regulation at 25°C). Youcanuse a 7805 for this, but it will be a bodge and is only advisable for rather tolerant loads.QuoteI think you're just missing some basic knowledge on how this thing works. The max input voltage of the LM317 is not specified, only the Vi-Vo. The circuitry is connected between those pins and will only see this voltage. As long as the voltage drop over the LM317 is less than 35V (or 37V, specs seems to differ slightly) you're ok. If the output get short circuited or the thermal protection kicks in you're in trouble. It will then lower the output voltage and the voltage over the regulator will exceed the max voltage and the unitwilldie, no matter how you hope and pray. A normal LM317 (there is a 57V specced LM317HV) will not tolerate 100V between any two of its pins. Higher voltage rating will require more silicon to accomodate larger depletion layers and it will cost you money. You can get a 125V/700mATL783for just a slightly higher price (but there's more, just do a search for one on Mouser or Digikey or so).The minimum output current for the LM317 is usually catered for by using the recommended resistor divider network with a 120 Ohm between VOand Adj. It will cause a current of ~10mA to flow, which is specified as being the upper limit in bias current, and no current will need to be drawn by any connected circuitry. That is why the minimum load current is explicitly in the datasheet of the LM317 and not in the µA7800 series datasheet (which coincidentally does not specify anything at all about its use under 5mA, which is kind of a fail). When using larger values for the top resistor you will at one start to have issues with voltages floating up, but the spread in bias currents is rather large and might not be an issue with every LM317 unit.

author: Zero999
author_rank: Super Contributor
timestamp: July 14, 2017, 12:11:14 pm
content: What's with all the bodging for linear regulators into poor references?If the TL431 isn't good enough, then how about the adjustable variant of the LM4041?http://www.ti.com/lit/ds/symlink/lm4041c.pdfVO= 5.333V1% values:R1 = 5k62R2 = 1k690.5% values:R1 = 14k2R2 = 4k27http://www.ti.com/product/LM4041-N/datasheet/application_and_implementation

author: 2N3055
author_rank: Super Contributor
timestamp: July 14, 2017, 12:20:45 pm
content: TL431 is better than 50 ppm/K and plenty accurate after trim. And cheap as dirt..

author: Zero999
author_rank: Super Contributor
timestamp: July 14, 2017, 01:30:25 pm
content: Quote from: 2N3055 on July 14, 2017, 12:20:45 pmI already suggested the TL431 on the first page of this thread, along with some resistor values to get damn near 5.333V, but it didn't seem to go down very well.https://www.eevblog.com/forum/projects/5-333-volt/msg1250984/#msg1250984

author: Crumble
author_rank: Regular Contributor
timestamp: July 14, 2017, 03:14:54 pm
content: I totally agree it would suffice, because in the original schematic it was tweaked by a pot anyway, so this can be done with the TL431 too. It is not specified to be better than 50ppm/°C, but it is within a reasonable temperature range around 25°C, but this is hardly an issue, nobody is going to use a synth at 100°C anyway. Sadly some claims came up about 7800 series regulators that IMO required amendment. I haven't actually heared from the TS for quite a while now, he might already have given up... Too much...

author: Zero999
author_rank: Super Contributor
timestamp: July 14, 2017, 03:20:35 pm
content: A bit off topic but I thought I'd post a link to the tool I used to calculate the resistor values. Enter the output voltage in the V1 box and the reference voltage of the programmable shunt regulator in the V2 box, select the resistor values, E6 to E192 and click calculate. It will spit out a few different resistor combinations which will give very close to the desired value. Obviously the results can be multiplied or divided by 10, if they're too low or high.http://sim.okawa-denshi.jp/en/teikokeisan.htm

author: JanJansen
author_rank: Frequent Contributor
timestamp: July 14, 2017, 03:46:04 pm
content: Quote from: Crumble on July 14, 2017, 03:14:54 pmNow i have a whole book to read here,i mean i wanto look at it if i order parts, ordering parts already cost a lot of time, i give up on this project.I mean : continue the blah, i will sort out the tips later, please post all tips together.

author: 2N3055
author_rank: Super Contributor
timestamp: July 14, 2017, 06:54:46 pm
content: Quote from: Hero999 on July 14, 2017, 01:30:25 pmI know, so did I allready... I just wanted to reiterate that this is going too far... Simple and adequate with a bit of security margin = good engineering...Take care!!

author: DBecker
author_rank: Frequent Contributor
timestamp: July 14, 2017, 07:06:22 pm
content: Quote from: Hero999 on July 14, 2017, 01:30:25 pmThe TL431 will work, but getting close to 5.333V is off-point. The circuit is tuned with a pot, and simply needs a temperate and age stable voltage source noticeably above that voltage.The original circuit used a 6.2V zener because that is a value where the different temperature effects came close to canceling each other out.

author: KL27x
author_rank: Super Contributor
timestamp: July 14, 2017, 08:35:18 pm
content: QuoteThat's great you're aware of that. I'm aware of that. The datasheet on this device, at least some of them, states max input voltage of 35V. Not stated or implied as Max Vi-Vo. You just made my point, thanks. If you understand how the device works, you can use it in ways that it is not specifically designed or spec'ed for.QuoteYou know this is for worst case scenario. This is with dirty, noisy Vin and variable/intermittent Vo. We both know you can get much better stability with much higher impedance resistor network under less demanding condition. 25 ohm resistor network is ridiculous. If conditions are this bad, you have more to worry about than your choice of regulator if you want to achieve high precision.QuoteNot at all. If you were to DESIGN a synth that needed a 5.33V regulator, you would spec an adjustable voltage regulator. This is what you will put in your schematic. Then when you go to BUILD the prototype, and all you have is the 7805, you might use that. If it works well enough for your goals, and if you have a bunch of these 7805 or a smoking deal on them, you might even use them in the production. Designing to get A+ in class and making something for yourself or for profit are different things.