Poor Man's Reference - Page 1
Forum section: electronics / general

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 02, 2017, 08:54:24 pm
content: here is an attempt at making a poor-man's reference.R4 controls the current and hence the tempco of the combination of D1/Q1and D1 can be a schottky or a germanium diode.the multipliers R1/R2 are modified according to voltage o/p requirement,opamp U1 selected for noise performance etc.,and finally the whole assembly could be ovenized.comments awaited from the most learned members of this forum.regards.

author: tablatronix
author_rank: Regular Contributor
timestamp: June 02, 2017, 09:20:01 pm
content: regarding poor mans references, I wonder if any consumer products use good vrefs worth salvaging.

author: cellularmitosis
author_rank: Unknown
timestamp: June 02, 2017, 10:52:43 pm
content: Throw the poor man's oven in there too!http://www.techlib.com/electronics/ovenckts.htm

author: cellularmitosis
author_rank: Unknown
timestamp: June 02, 2017, 11:00:10 pm
content: (here is some data I took on that circuit recently:)

author: cellularmitosis
author_rank: Unknown
timestamp: June 02, 2017, 11:55:33 pm
content: @evb149 oh cool! I recently noticed in digikey that a few of the TL431 variants advertised a 20ppm/C tempco for a very low price. I ordered a few of each and am planning to do a little round-up test with a little mini-fridge and temperature controller which I just recently picked up.

author: pitagoras
author_rank: Regular Contributor
timestamp: June 03, 2017, 12:30:29 am
content: There is a good thread started by mr hoffman about classical referencesEdit: thishttps://www.eevblog.com/forum/metrology/old-fashioned-zener-10v-reference/

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 03, 2017, 02:20:37 am
content: Quote from: pitagoras on June 03, 2017, 12:30:29 amthere is nary a zener in sight.regards.

author: David Hess
author_rank: Super Contributor
timestamp: June 03, 2017, 03:50:23 am
content: Quote from: evb149 on June 02, 2017, 09:39:27 pmWeigh scales are ratiometric so a precision reference is not needed; the output from a mediocre voltage regulator is good enough.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: June 03, 2017, 01:47:15 pm
content: Never played with a diy one, but how about making a bandgap reference with a couple transistors. Can't get any cheaper than that.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 03, 2017, 02:47:14 pm
content: Quote from: Conrad Hoffman on June 03, 2017, 01:47:15 pmhello sir,this reference relies on band-gap difference of si and ge (or schottky si).regards.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: June 03, 2017, 03:30:27 pm
content: Ah, yes it does! Will R4 bring it through zero TC over a reasonable range? A conventional bandgap uses matched parts so I'd expect it to work over a wider range, but only a test will prove which is better.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 03, 2017, 04:18:52 pm
content: I won't expect the shown circuit to work well with a schottky diode. My first guess would be more like an PAT temperature sensor, so an output voltage proportional to absolute temperature. At least this is what one would expect to get with a lower forward voltage silicon diode.The bandgap reference only needs matched or accurately scaled parts to get compensation of the TC with a fixed gain circuit. With an adjustment one could compensate for this. The limitation is that there is not only a linear TC, but also a small second order term.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 03, 2017, 05:00:53 pm
content: Quote from: Conrad Hoffman on June 03, 2017, 03:30:27 pmcurrently testing using a diode-connected OC28(Ge) thermally coupled to a 2N5038(Si).also if anyone could comment on using a BFP420(SiGe) transistor connected as a diode coupled with a regular Si.more comments / analysis are welcome.regards.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 03, 2017, 05:24:32 pm
content: I would not expect too much with different diodes Transistors if they are still Si based (SiGe is mainly strained Si). It does not make any sense to use an expensive diode / transistor to make a reference less capable than an TL431. Even Ge Diodes are expensive now.In an older thread about alternative low cost reference circuits, there was one using an LED and transistor as emitter follower. This might give something like 1.4 V with low TC if suitable currents are used.Another reasonable stable voltage is from a dry cell (old style Zn-MnO2, not alkaline) or Ag based coin cell, though usually already more expensive than a TL431.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 03, 2017, 06:00:07 pm
content: Quote from: Kleinstein on June 03, 2017, 05:24:32 pmthank you very much sir,please have a look at this too, i am awaiting your valued comments.regards.

author: David Hess
author_rank: Super Contributor
timestamp: June 04, 2017, 12:28:05 am
content: The +2mv/C temperature coefficient of a red LED can be used to compensate the +2mv/C Vbe of a transistor to make a current reference. Add another resistor and it becomes a voltage reference.All of the various cheap references like the TL431, LM336, LM385, LM4040, and LM4041 have about the same best case temperature coefficient of 20ppm/C.The cheapest good reference is a 6.2V zener in series with a Vbe to cancel out their opposite 330ppm/C temperature coefficients.The zener reference in a 723 might drift as much as 150ppm/C however the rest of the IC could be configured to maintain a constant temperature like a LM339 reference does. This might be the least expensive better than 20ppm/C reference.A transistor Vbe multiplier could be adjusted to compensate for the temperature coefficient of a higher than 6.2 volt zener diode.Many of these solution benefit from bootstrapping but the extra parts make the 20ppm/C integrated bandgap references more economical.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 05, 2017, 09:18:58 pm
content: i tested the following contraption to the limits of my measurement which is a *measly* hp3468a. (reading confirmed with hioki 3237).both meters' calibration status - unkown.R5 is a carbon resistor acting as a 0.5watt heater.R3 is the bias control resistor. (carbon composition +- 10%)the transistors are bolted together and circuit wired point to point using normal Pb/Sn solder.the whole contraption put in a metal candy box and filled with silicone oil.the box put in a styrofoam box and stuffed with an old t-shirt.the circuit takes 1.5hrs to stabilize and the output voltage stabilizes to 0.47620 volts,reading stable for two days now.ambient has been varying from 35 to 40 degC. (yes it is very hot here !)looks like a pretty stable ref. to me considering no op-amp boosting, or precision resistor or any active temp. control.comments required.regards.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 09, 2017, 07:26:56 pm
content: update:R3 & R4 control the tempco, and since the schottky diode has a tempco of ca. -1.5mv/degC and silicon diode has a tempco of ca -2mv/degCusing 4 schottky diodes gives a combined tempco of -6mv/degC and 3 si diodes give a tempco of -6mv/degC. the combined effect can befine tuned by R3 + R4 to get to 0 tempco.R1, R2, R5 and R6 can be a single tcr tracking resistor array. (like LT5400). or PWW's.comments from learned members of the forum required.regards.

author: David Hess
author_rank: Super Contributor
timestamp: June 09, 2017, 10:00:42 pm
content: Here is another reference I just ran across in National's LF355 datasheet. It relies on setting a JFET to its zero temperature coefficient point and converting the resulting constant current to a voltage with a resistor.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 09, 2017, 10:07:44 pm
content: i think alex nikitin has made something similar, and the performance is also pretty good according to him.regards.

author: David Hess
author_rank: Super Contributor
timestamp: June 09, 2017, 10:28:11 pm
content: Quote from: zhtoor on June 09, 2017, 10:07:44 pmIf you are talking about the zero temperature coefficient JFET reference, I know someone on the forums was messing with it a couple months ago. Considering how cheap 20ppm/C bandgap references are, it really does not pay to hack together anything which has a worse temperature coefficient.Adjusting a JFET to its zero temperature coefficient point explains why several older DMMs were able to use them as simple buffers. These DMMs have the advantage of no charge injection unlike a modern chopping or autozero design.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: June 09, 2017, 11:08:36 pm
content: Quote from: David Hess on June 09, 2017, 10:28:11 pmMy 10V JVR sample has a tempco under 1ppm/C in 22C-26C range and stability was better than 10ppm/year for 10V output (that includes the resistors drift as well). Hysteresis is low and the noise is on par with buried zeners of LM399 variety at only 1.5mA JFET current. So it is better in almost all respects than bandgap references and considering that you can buy a metal can 2N4391 JFET for $2 it is certainly worth the effort IMHO.CheersAlex

author: David Hess
author_rank: Super Contributor
timestamp: June 09, 2017, 11:48:22 pm
content: Quote from: Alex Nikitin on June 09, 2017, 11:08:36 pmA 20ppm/C maximum bandgap reference which requires no adjustments other than tolerance and practically no additional cost in parts is 50 cents. The next step up from that is a $4 2.5ppm/C reference. The JFET reference needs a lot of trimming and auxiliary parts.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: June 10, 2017, 12:47:34 am
content: Quote from: David Hess on June 09, 2017, 11:48:22 pmIt all depends on your requirements. No bandgap reference I know of can give you 10ppm/year stability in a hermetic package and the LF noise below 1ppm p-p.CheersAlex

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 10, 2017, 03:38:11 am
content: semiconductor companies design chips for high volume manufacturability and/or testability. furthermore their foundry process isthe constraint they have to work in, whereas for a discrete design, individual design elements are available for optimization tocreate a better performing design by trading large volumes with small, simple testing vs complex, simple adjustment vscomplex adjustment and all for an end, that is; better performance for some particular purpose as alex nikitin pointed out.as they say, engineering is the art of tradeoff / compromise.regards.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 10, 2017, 04:52:42 am
content: Quote from: evb149 on June 10, 2017, 04:31:02 amwell, i have been looking for high purity cadmium rods, (mercury, sulfuric acid etc. is available in pakistan).regards and thanks for your appreciation.

author: Marco
author_rank: Super Contributor
timestamp: June 10, 2017, 05:00:05 am
content: Quote from: David Hess on June 09, 2017, 10:28:11 pmThe best of which used auto-calibration. Auto-calibration is just really slow chopping ...

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 10, 2017, 05:08:59 am
content: Quote from: evb149 on June 10, 2017, 04:31:02 ami am surprised that you are surprised. if we look around us, are the women cooking what they used to? we used to cook delicious bread athome, make all kinds of fantastic edibles at home including jams, breads cookies etc., we used to do a lot of tinkering at home, almostevery household had a workshop. but alas, we have now become a "consumer" society (both eastern and western included), we are toldto consume brand "x" over brand "y" (a la, ADR431 over LM399). our older generation was a lot more active than us, they used to workhard, and we consume.sorry for the rant, but i felt that you may understand.regards.

author: Marco
author_rank: Super Contributor
timestamp: June 10, 2017, 05:32:33 am
content: Quote from: evb149 on June 10, 2017, 03:05:24 amDunno about XFET, but Intersil's FGA relies on an EEPROM type process with junction diodes, which will include a passivation layer. That's hermetic, more prone to stress than a nice roomy can though.

author: Andreas
author_rank: Super Contributor
timestamp: June 10, 2017, 05:36:24 am
content: Quote from: Alex Nikitin on June 10, 2017, 12:47:34 amHello Alex,the LTC6655 in LS8-package is very close to this.And I bet that also there will be a good stability at least after a run in time.Unfortunately I have no own data for long term for this device.With best regardsAndreas

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 10, 2017, 06:09:03 am
content: could'nt have said it better evb149.so count me in, viva la resistance !regards and may your tribe increase !

author: Kleinstein
author_rank: Super Contributor
timestamp: June 10, 2017, 09:02:45 am
content: If you want to build a DIY votlage reference, I would not worry so much about the TC. The really difficult part is long time stability. For the TC in a DIY reference circuit there often is a way to tune the TC close to zero (e.g. by adjusting the current to a zener type reference). This usually only works good for a small temperature range - but than a coarse temperature stabilization (e.g. a small oven) can do a lot. If you have time for a DIY circuit adjusting an operating point can be used, that is less practical in a monolithic chip.For long time stability, a critical point might be the drift of resistors. To get a small effect there, a rather nonlinear I/U curve is needed, like a low differential resistance for a zener. It does not really help if you can build a circuit from cheap semiconductor, like of the shelf transistors, but need super stable resistors to make is stable. Even with the LTZ1000 circuit, it takes quite good resistors - and this is a circuit that is already really good in being not so sensitive to the resistors.

author: David Hess
author_rank: Super Contributor
timestamp: June 10, 2017, 02:04:32 pm
content: Quote from: Marco on June 10, 2017, 05:00:05 amJust like drift is just really low frequency noise.I keep these old JFET input multimeters around as a sanity check for when I suspect charge injection from one of my more modern multimeters is causing problems.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 10, 2017, 03:07:17 pm
content: Quote from: Kleinstein on June 10, 2017, 09:02:45 ami agree with you completely.what i gather from learned people like yourself, MisterDiodes and Mr. Edwin, the three cardinal pillars of references are:-1. the *resistor* and their ratios, and their stability.2. stability of the central stability element (zener etc.).3. tight environmental constraints (like temperature, humidity, mechanical stress etc.).regards.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 10, 2017, 05:03:29 pm
content: The circuit / central reference element determines how stable the resistors need to be:With the JFET+resistor, JVR type reference, a drift in the resistor translates nearly 1:1 (maybe a factor of 0.5) toward the reference voltage.The bandgap type circuits are also quite sensitive to resistor / current matching. The initially shown circuit the a Si transistor and a Ge diode might in this respect be actually be relatively good, as uses the same current with parts in series - however Ge transistors are even known to show significant aging, as diffusion in Ge is rather fast. So I won't expect a Ge diode to be super stable.With a good zener or the LTZ1000 circuit it can be about a factor of 100 lower than the resistor drift.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: June 10, 2017, 05:22:01 pm
content: Quote from: Kleinstein on June 10, 2017, 05:03:29 pmThat is not so. The resistor drift in the JVR circuit is attenuated considerably, depending on the JFET used. With the 2N4391, the attenuation factor should be at least 20, so a 20ppm shift in the resistor value will create only 1ppm shift in the output voltage. If the JFET and the resistor are thermally coupled, it should be even possible to compensate for the resistor TC in a certain range of temperatures by adjusting the JFET current.CheersAlex

author: Marco
author_rank: Super Contributor
timestamp: June 10, 2017, 05:36:26 pm
content: Quote from: Kleinstein on June 10, 2017, 05:03:29 pmOnly because he amplifies it to 10V, just the source voltage alone will attenuate the resistor drift by the inverse of transconductance.

author: Vtile
author_rank: Super Contributor
timestamp: June 10, 2017, 09:55:07 pm
content: Can someone open a bit of the charge injection mentioned many times. How it is seen and in what magnitudes. Is it a transient kind of effect.I think I will build a "poor mans reference" some day, but I haven't decided if I go with Conrads 10V opa design or BJT sourced zener like in that Voltage source/reference (1n8xx) Dave have. Well my best digital meter shows full 3,5 digits so not much on it but keeping up old 7th hand equipment would be easier with bunch of precision resistors and voltage ref and my 2nd old FET nA/uV meter need some love.I have also been wondering how to amplify the ref voltage to 100V or 200V even with some long term and temp stability... Somekind of OPA controlled transistor driven voltage divider.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 11, 2017, 12:04:06 am
content: both conrad's design and dave's are based on temp. compensated zeners, 1N8xx are especially good at stability if operated right, if you can find them!.regards.

author: David Hess
author_rank: Super Contributor
timestamp: June 11, 2017, 09:09:23 am
content: Quote from: zhtoor on June 11, 2017, 12:04:06 amThey are very available but cost $10 or more. For that price, you can buy an awful lot of performance in an easier to use integrated reference.

author: David Hess
author_rank: Super Contributor
timestamp: June 11, 2017, 09:54:27 am
content: Quote from: Vtile on June 10, 2017, 09:55:07 pmThe FET switches used for automatic zeroing and chopping inject charge at the input of the multimeter. This can either disrupt circuit operation or if it is synchronous with noise coming from the circuit, the intermodulation will produce a DC offset or low frequency tone. It shows up as inexplicable noise, drift, or DC offset.I remember it showing up in precision circuits using the OP-07 and various chopper stabilized amplifiers with levels of 10s to 100s of microvolts of offset. In those cases the easy solution was to add a 10uF aluminum electrolytic capacitor from the output of the operational amplifier to ground. The large value combined with the finite output resistance of the operational amplifier does not oscillate because the frequency response falls off at such a low frequency but the capacitor also provides a low AC output impedance blocking the charge injection. Something similar is often recommended now for driving the input of sampling and delta-sigma ADCs for the same reason.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 11, 2017, 03:31:42 pm
content: update:i came across an interesting paper discussing 1nv measurements against a JJA using a transfer standard :-http://ieeexplore.ieee.org/abstract/document/109957/the transfer standard is discussed in :-http://iopscience.iop.org/article/10.1088/0022-3735/5/10/026/metaboth files attached.it looks like alex nikitin is definitely on to something..... see attached circuit and simulate it using ltspice.regards and comments required.

author: Vtile
author_rank: Super Contributor
timestamp: June 11, 2017, 06:14:37 pm
content: Oh, I so like this metrology grade temperature chamber used. Also fits to title of this thread.Quote

author: Marco
author_rank: Super Contributor
timestamp: June 11, 2017, 07:09:01 pm
content: What's also interesting is that a temperature chamber with discrete components was able to get that kind of stability.Guess there isn't a huge need to get everything monolithic (as long as you don't mind it being a little larger).

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 13, 2017, 07:01:09 pm
content: has anybody tried a supercap to filter out noise across a zener diode like 1N829A?or maybe think of a rechargeable battery as a *really* supercap?the noise perfomance could be interesting.regards.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 13, 2017, 08:05:12 pm
content: followup:-please see attached diagram. the batteries are connected in a way that they are trickle charged tofully charged state of (2.3*3 = 6.9V for lead acid cells), ie; the nominal reference voltage ofLM329/LM399.here the intent is to use the battery as a *really* supercap, and i think we all know the noiseperformance of lead acid batteries.regards and comments required.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 13, 2017, 08:25:04 pm
content: The LM329 / LM399 has a really low impedance. So even with a large "capacitor" there will not be that much filtering. Also, if for some reason (e.g. temperature rise or mechanical disturbance) the voltage in the cells increases, there can be quite some extra current to the reference - possibly too much. So it would need some kind of resistance / current limit.Lead Acid cells have a significant self discharge. So it takes a noticeable current to keep a constant voltage. There also is a significant temperature dependence of the voltage and leakage current. So for a stable output it would need a really stable temperature.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 13, 2017, 08:29:35 pm
content: Quote from: Kleinstein on June 13, 2017, 08:25:04 pmagreed, but the equivalent "capacitance" of a battery would be *huge*, for example, 1AH batterywould be approx. Q=it = 1*3600s = CV => C = 521F (!) at 6.9V (please check my calcs, or am i out of my mind?)so a 1 ohm dynamic impedance translates into RC = 521 seconds. a lower cutoff freq 0.0003Hz.also supercaps can be used, especially maxwell ones, which have been tested for noise performance.yes, if we have carefully controlled conditions, the noise floor could be difficult to detect.maybe doing this to ltz1000 zener or 1N829A would be better?regards.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 15, 2017, 08:44:51 pm
content: hello all,help required.i am trying to simulate the reference part of LM399 (LM329) using ltspice, but running into trouble,maybe i am using the wrong transistors, (i am using THAT3XX models), or can't adjust the resistors marked for factory adjustment,or maybe using 6.2V zener instead of 6.3V is a problem. (maybe use 2DW232 model here?, could be interesting)the voltages and currents work out approx. ok but i should see a hump for a temperature range 0-100degC around 90deg, or anyhump at all, which i cant see.i have also tried to simulate for a hump using the tesla supplied schematic diagram, (i do see a hump in the bypass transistor collector currentwhich is only in the tesla schematic as T18).attached is the schematic / ltspice file.comments required from learned members of this forum.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 16, 2017, 07:44:48 am
content: The details of the performance depends on the details of the models for both the transistors and the zener. Especially the buried zener might be a little different from the simple models.Anyway The shunt regulator type circuit in the LM399 is more a convenient replacement for a normal zener, but it also has drawbacks from thermal effects. So it likely is not a practical solution for a circuit build from separate parts. The LTZ1000 circuit, with an external OP is more realistic to build from separate parts. Here it only needs the zener and one transistor to be thermally coupled and in addition the power dissipation of that part is essentially constant. OPs are cheap - so there is no need to do all the gain / loop part by hand.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 16, 2017, 08:03:42 pm
content: Quote from: Kleinstein on June 16, 2017, 07:44:48 ami agree, LTZ1000 is a *LOT* simpler, but:-the number of active elements are like 4xNPN and 3XPNP looks like an ideal candidate for implementation on a low-noisetransistor array die from THAT, ie; THAT380G which is 4 matched NPN *AND* 4 matched PNP's on the same die, availablefreely (cost unkown to me yet!, i have access to a couple of THAT300's, 320's and 340 matched arrays). moreover, understandingthe internal workings of the reference may be useful in coming up with an LM399 like circuit for higher zener currents -> lower noiseperformance and/or using 2DW232 type lownoise zeners coupled with a discrete implementation using 4XNPN array (THAT300)and 4XPNP array (THAT320).by tweaking the marked factory adjustable resistors, i *was* able to see some funny activity in d/dtemp (derivative of stabilized voltageagainst temp) in the design. i suspect that either the indicated schematic is missing some elements (refer to an internal circuit bytesla - an LM399 clone) or the values on the adjustable resistors are a problem.i think we *should* be able to come up with a *reasonable* simulation of the LM399 schematic, or at least do an opamp style equivalentof the schematic.maybe help from Robert Dobkin could be arranged by someone? (diligentminds.com?)regards and thanks for helping out.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 17, 2017, 08:31:04 am
content: In the LM199 type circuit model shown below, the only really important transistor that might have a significant influence on the noise and TC is the Q4 NPN transistors. The other transistors are less critical by something like a factor of 100. Q1-Q3 make a more or less constant current source. Together with Q4 this gives a reasonable high DC gain. Q5 and Q6 than are responsible for a high current gain.However it is not at all attractive to have Q6 on the same die - its heat is a big problem and transistor matching is not needed at all. It only the current mirror around Q1,Q2 that really needs matching - but this is more like used because the matching is available on the chip. A simple resistor, like in the LTZ1000 circuit could replace it as well, or maybe even better.Anyway the zener noise is usually still higher than that of the transistor, and for a single resistor there is no need for a relatively expensive / exotic transistor array. The point where a single die construction would help is with the zener and the one transistor and maybe a diode / transistor used as a temperature sensor. The THAT3xx however are in a plastic case and thus not expected to be very long term stable. Extra gain is best provided by an external OP - noise of the OP is not critical. In principle the LTZ1000 circuit might still meet the chips specs (TC, stability) with using an LM358 OP - one would hardly notice a difference to the more normal LT1013. So the external OP it not even critical.If at all, a slight improvement in the LTZ1000 could be in better TC matching of zener and transistor (e.g. slightly lower zener voltage or larger area transistor) , so that the intrinsic TC could be a little lower.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 17, 2017, 11:41:47 am
content: Quote from: Kleinstein on June 17, 2017, 08:31:04 amthanks sir,Q3, in my humble opinion the most important transistor, since it is the one which is acting as a main compensation device for the zener.regards.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 17, 2017, 01:59:38 pm
content: Q3 is not the main transistor working together with the zener. It is more like a constant current source. In the simulation one could replace Q1,Q2,Q3 with just a resistor to the positive supply, or replace Q3 with a resistor. The rather high emitter resistor reduces the voltage gain of that stage quite a lot.The transistors Q1-Q4 are likely of different size, so intentionally not matched but more like scaled like in a bandgap reference. More like Q3 larger (e.g. 4 times) than Q4 and and Q2 larger than Q1.With same size transistors it is understandable that the simulation did not work as expected.The transistor that sets the final voltage is more Q4. At least this way the circuit makes perfect sense.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 17, 2017, 02:28:49 pm
content: Quote from: Kleinstein on June 17, 2017, 01:59:38 pmthanks again.have you simulated by using different sized transistors? if yes can you share the source file for my benefit?regards.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 17, 2017, 04:54:30 pm
content: I have not simulated the circuit. The different size conclusion is just conventional circuit analysis in the head, like done before simulations:The two transistors with the modified current mirror (Q1+Q2 and Q3+Q4) gives a lower current in the leg with the resistors. So with same size transistors one would get I(Q3) < I(Q4) and I(Q2) < I(Q1). As I(Q1) = I(Q3) and I(Q4) =~ I(Q2) this would not work. To make it work one would need to compensate for the drop at the resistor by using a larger area transistor there. To a first approximation this would make this a current source proportional to absolute temperature. So at the controlled temperature a constant current.

author: zhtoor
author_rank: Frequent Contributor
timestamp: June 19, 2017, 03:17:19 pm
content: Quote from: Kleinstein on June 17, 2017, 04:54:30 pmlooks like you are right.here, directly from the horse's mouth, find attached the original dobkin paper about lm199.regards.