high voltage current source (mirror) - Page 1
Forum section: electronics / projects

author: coppercone2
author_rank: Super Contributor
timestamp: November 03, 2024, 10:18:19 pm
content: I am still looking for a high voltage circuit that can be used with the 1200V keithley power supply (voltage source) to regulate constant current.Maybe its the wrong way to go about it, but is some kind of current mirror possible?i.e. circuit 1 : 1-10mA current source (HP lab equipment)circuit 2 : power by 1200V keithley power supply, mimics the current of circuit #1The full output of the keithley is 10mA @ 1200V roughly.It would be for biasing resistors for testingI thought maybe this kind of cirucit would just connect to the 2 test equipment and not need any power source etc?

author: TimFox
author_rank: Super Contributor
timestamp: November 03, 2024, 10:23:39 pm
content: Have you considered using a vacuum tube circuit?

author: coppercone2
author_rank: Super Contributor
timestamp: November 03, 2024, 10:24:57 pm
content: no because it has suppliesI thought with a advanced piece of equipment like the HP current source that is precise, it might be possible to make something that just has 4 banana connectors, 2 into the keithley and 2 into the HP without any power or etcsimple. Stack them, plug it in, measure.Can't a current mirror do this? It would not even need a bias resistor for the set side since its connected to a real current source .like this guy herehttps://www.digikey.com/en/products/detail/rochester-electronics-llc/2SC4636LS/121104285mA would be plenty.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: November 03, 2024, 10:39:01 pm
content: Quote from: coppercone2 on November 03, 2024, 10:24:57 pmSo you mean a high voltage battery inside the box ?There are 4 terminal parts (no hidden batteries) that take current in and deliver current out, called Photovoltaic isolators.Of course they cannot give free energy, so the output power is a fraction of the input power.eg TLP3906 has 10mA and 1.65V in and 9V OC and 30uA SC outthat's 16.5mW in and 216uW out. Power transfer ratio = 1.3%

author: coppercone2
author_rank: Super Contributor
timestamp: November 03, 2024, 10:40:50 pm
content: the current mirror always shows two things, left and right side.left side = lab current sourceright side = keithly + loadit looks like I don't need another thing for it on the most basic level. I am sure a HV capable current mirror has some problem but I thought maybe.

author: coppercone2
author_rank: Super Contributor
timestamp: November 03, 2024, 10:43:09 pm
content: Like this. I bet something bad would happen to the lower voltage supply though without more parts

author: inse
author_rank: Super Contributor
timestamp: November 03, 2024, 10:44:09 pm
content: Maybe you can find some inspiration in my thread:https://www.eevblog.com/forum/projects/high-voltage-constant-(low)-current-load/If precisely adjustable current is required, add an OPAMP to drive the kaskode circuit

author: coppercone2
author_rank: Super Contributor
timestamp: November 03, 2024, 10:46:42 pm
content: I really don't want any components that require ANOTHER power supply.I thought maybe this thing can get 5% accuracy from using only the keithley and HPI will look at the thread but I don't want op-ampsIf this can work its very elegant. A few transistors in a box that connects to two lab equipment to bias a resistor.If it needs batteries and op amp power supplies and blah blah its not worth doing.I thought discussing a current mirror would be worth while, no one really makes them for anything I know of, they are taught but its not popular to make for some reason.Both the keithley and HP are full of high quality parts and are both very stable. They have range switching, potentiometers, low drift, etc. If I can only find some simple way to link them, I think it would be very nice.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: November 03, 2024, 10:57:49 pm
content: Quote from: coppercone2 on November 03, 2024, 10:43:09 pmIf you want a grounded load, you are looking for a current mirroranda lever shifter.Standard current mirrors do what the name says, they take a current fed to a common rail and reflect that using the same rail.That means a high side load.If you want no external low side power, then the circuit needs to power off the low side current source (see 4-20mA current loop designs for ideas)

author: coppercone2
author_rank: Super Contributor
timestamp: November 03, 2024, 10:58:34 pm
content: Well its for measuring the voltage drop of a passive component I don't care if its high or low side if thats what you mean? I.e. it has to be transistor supply side for simpler implementation? That is more then OKI am not sure what you mean by the 4-20mA loop. I was just thinking about this from the perspective of a simple textbook current mirror (there is many types with varying amount of transistors). I don't know which would be appropriate to analyze for this idea.

author: coppercone2
author_rank: Super Contributor
timestamp: November 03, 2024, 11:05:05 pm
content: I redrew it to what I think you mean

author: tggzzz
author_rank: Super Contributor
timestamp: November 03, 2024, 11:05:19 pm
content: Quote from: coppercone2 on November 03, 2024, 10:18:19 pmSeveral examples are notes here:https://www.eevblog.com/forum/projects/high-voltage-constant-(low)-current-load/msg5299519/#msg5299519and the reference goes into much more detail

author: inse
author_rank: Super Contributor
timestamp: November 03, 2024, 11:05:41 pm
content: Finding and sourcing a transistor capable of regulating 1.2kV at 10mA (12W max power dissipation in case of short circuit) might also be challenging.That’s why I mentioned my thread

author: tggzzz
author_rank: Super Contributor
timestamp: November 03, 2024, 11:07:32 pm
content: Quote from: inse on November 03, 2024, 11:05:41 pmIt is relatively easy to distribute the voltage and power across multiple HV MOSFETS; seehttps://www.eevblog.com/forum/projects/high-voltage-constant-(low)-current-load/msg5299519/#msg5299519

author: PCB.Wiz
author_rank: Super Contributor
timestamp: November 03, 2024, 11:07:39 pm
content: Quote from: coppercone2 on November 03, 2024, 10:58:34 pmSure, you can just connect two of those 2SC4636LS parts as a classic current mirror. The load goes between the collector and 1700V.Emitter resistors can reduce matching errors and give you some gain choices.Quote from: coppercone2 on November 03, 2024, 10:46:42 pm5% will be a serious challenge, look at the Ib/Ic curves on that part, and you see for a given Ib, Ic varies significantly with voltage.

author: coppercone2
author_rank: Super Contributor
timestamp: November 03, 2024, 11:10:35 pm
content: Ok. How about increasing the number of transistors to make the improved mirrors? I remember a text book had many.What situations is it dangerous for the 6181C though? Because I don't want to fry it. Though, for the start I can use some 9V powered 317 regulator current source, I don't care if it breaks, just needs a good setup to ensure HV safety (neat), for first developmentsI can set the voltage on the keithley to 1V accuracy BTW, so that is kind of 'ranging' I think. So I can set the supply of the mirror to any voltage.I thought to put a MOV across the current source too, so if the HV gets into the left side, it should be limited to the MOV voltage and prevent it from getting dangerously energized by the HV supply? And a neon light to show HV fault (it won't glow unless its zapped)I think I will try it. All the resistors and switches etc... I need to see how accurate it is in the most basic form, I had enough wires for the rest of this year... I was hoping all the hardware inside of those test equipment might let me get away with making this part simpler. I will make a plastic rod to adjust the LM317 with in the test prototype for safety reasons

author: PCB.Wiz
author_rank: Super Contributor
timestamp: November 03, 2024, 11:38:13 pm
content: Quote from: coppercone2 on November 03, 2024, 11:10:35 pmHere is a starting point, to give you some ballparks.You can get a rough fix-up for the slope of Ic/Vce, using a resistor, that varies by part, so you need to experiment.Here I chose 3 high voltage parts on LTSpice.The worst NPN part corrects to to 2.4% 10-200V, with R7 = 1Meg. With No R7 varies appx 5.3%Finer trim of R7 = 1.17M balances the 'parabola' and corrects to ~1.72%

author: coppercone2
author_rank: Super Contributor
timestamp: November 03, 2024, 11:40:20 pm
content: Ok I bought 6x 2SC4636 for fun. I never did anything with a HV transistor beforeThe purpose of this was to find dodgy resistors that don't like HVMy old thread was about trying to do this with just the keithley, but someone hypothesised it would only get to maybe 30% accuracy on the constant current source. Maybe by adding the mirror, it could get alot nicer. This idea started when I realized you can test a power diode with just a beefy current limited power supply with pretty high confidence.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: November 03, 2024, 11:57:36 pm
content: Quote from: coppercone2 on November 03, 2024, 11:10:35 pmAny slip to 1700V will be risky.Because the source is current, you can add series R's and Zener clamps - 1k of total series will drop 10V at 10mA, and can source 1.7A on a oops.So the zeners/TVS/TSS need to be good enough to sink 1.7A ballpark.

author: tggzzz
author_rank: Super Contributor
timestamp: November 04, 2024, 12:02:59 am
content: Quote from: coppercone2 on November 03, 2024, 11:10:35 pm13 pages of high quality circuits in the refs inhttps://www.eevblog.com/forum/projects/high-voltage-constant-(low)-current-load/msg5299519/#msg5299519plus other pages in TAoE.Or you could reinvent an elliptical wheel.

author: coppercone2
author_rank: Super Contributor
timestamp: November 04, 2024, 12:07:20 am
content: Ok I am just gonna try the basic one first that circuit in the picture looks very complicated , perhaps I will figure out why it was made when I see the deficiencies of the first one

author: tggzzz
author_rank: Super Contributor
timestamp: November 04, 2024, 12:30:44 am
content: Quote from: coppercone2 on November 04, 2024, 12:07:20 amThe strengths and weaknesses of each circuit are clearly explained.Just get TAoE and TAoE x-chapters. You won't regret it.

author: SiliconWizard
author_rank: Super Contributor
timestamp: November 04, 2024, 12:42:24 am
content: Cascade several FETs. Yes I think it's been talked about before.Then call Electroboom before you turn it on.

author: coppercone2
author_rank: Super Contributor
timestamp: November 04, 2024, 12:46:26 am
content: ok I will try it with 2 bjt before we make it into the manhattan project with mosfet cascodesI have TO220 sockets to make this easy

author: PCB.Wiz
author_rank: Super Contributor
timestamp: November 04, 2024, 02:42:52 am
content: I've updated #16 with a couple of 3-element current mirrors, that allow either MOSFET or BJT main active part and use (matched) small signal NPN as compare elements.This improves thermal tolerance as the power device is no longer a reference element, and the output impedance effects are corrected by the feedback.More voltage is needed across the current source.

author: coppercone2
author_rank: Super Contributor
timestamp: November 04, 2024, 02:46:55 am
content: the 6181A is a 110V capable current sourceI think I have some matched NPN transistors so it might be interesting to add that in

author: coppercone2
author_rank: Super Contributor
timestamp: November 04, 2024, 02:55:28 am
content: Yeah I have a MAT12 from some failed circuit desoldering it nowi been meaning to do that for about 3 years lolok wow that was bad to desolder that rat hole pcbThe MAT12 says 1310 HFE for both sides on the new DCA75 meter, what ever its worthI also have a darlingon dual matched NPN from the 6177A, that one says hFE 91 and 96 for each side, but it incorrectly reads darlingtons IIRC

author: PCB.Wiz
author_rank: Super Contributor
timestamp: November 04, 2024, 03:41:39 am
content: Quote from: coppercone2 on November 04, 2024, 02:46:55 amYou have plenty of voltage overhead, so matching is merely 'nice to have', as the emitter resistor here can have relatively large drops.With 500R, you have 1.5V at 3mA and 5V at 10mAThose MAT12 sound rather too nice to use in this application. You do not need low noise and uV offsets, if you seek better than 5% tracking.

author: coppercone2
author_rank: Super Contributor
timestamp: November 04, 2024, 04:26:58 am
content: i think its the only one I got and its been dormant for years but I can just try it with unmatched transistor first 'i guess I can throw something on a future digikey order there is no need to miser that hardactually wow there is slim pickings for through hole matched devices! I want end to the war on wires and low inductance obsession

author: inse
author_rank: Super Contributor
timestamp: November 04, 2024, 04:57:59 am
content: Cool, you found a source for single 2SC4636‘sFarnell is funny: they have 44 pcs in stock but would only sell in multiple of 75 😁

author: coppercone2
author_rank: Super Contributor
timestamp: November 04, 2024, 05:08:54 am
content: I found 2SK2368's in my junk boxcould they be used for a stop gap circuit @ 400V? it has 500V ratingbut it would give me something to do

author: PCB.Wiz
author_rank: Super Contributor
timestamp: November 04, 2024, 08:23:51 am
content: Quote from: coppercone2 on November 04, 2024, 05:08:54 amIf using a FET, you would need some care to avoid instant connect to high voltages, as that high dV/dT can stress the gate.Ideally, always connect first before increase of voltage, but who remembers to do that 100% of the time ?A simple RC to the HV pin and a clamp zener on the gate, should reduce slew related voltage transfer.The feedback transistors will also work to clamp, but they have a finite response time, and finite current.

author: coppercone2
author_rank: Super Contributor
timestamp: November 04, 2024, 05:32:52 pm
content: I’ll wait for the bit to see if it works before the mosfet test. But those might be a good to experiment on before burning 1800v fets.The problem with the bjt is that the base is steaming some current right?

author: SiliconWizard
author_rank: Super Contributor
timestamp: November 05, 2024, 03:15:20 am
content: Have you had a look at the IXYS MOSFETs? It's expensive sh*t but... Like the IXTF1N450.

author: coppercone2
author_rank: Super Contributor
timestamp: November 05, 2024, 03:20:43 am
content: I thought the linear ones might be good but it only goes to 600V but I wonder if series linear mosfet might be better then trying to deal with a single regular mosfet

author: coppercone2
author_rank: Super Contributor
timestamp: November 05, 2024, 03:24:04 am
content: https://www.mouser.com/ProductDetail/IXYS/IXTN17N120L?qs=t7yjd2JO%2FgRTGaFLcAe16Q%3D%3Dmaybe it might be worth it? its a bit expensive

author: TimFox
author_rank: Super Contributor
timestamp: November 05, 2024, 04:06:23 am
content: IXYSdepletion-modeMOSFETs can be made into current sources--you may need to cascode them for higher voltages.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: November 05, 2024, 05:15:41 am
content: Quote from: coppercone2 on November 04, 2024, 05:32:52 pmIf you want some dynamic range, a bigger problem is thechangein HFE.You can adjust the gain ratio to compensate for a fixed base current offset error, but if HFE varies with current (as your Sanyo example does) you have to pick some average compensate.You might be ok with your 5% target, you would need to measure the parts when they arrive.lcsc have many 1700V MOSFETS from a couple of dollars. They avoid the HFE linearity issue, but have capacitive effects you need to manage.Run some spice tests with rapid ramping high voltages, and you can see the gate-coupling effects and how the currents want to flow.

author: coppercone2
author_rank: Super Contributor
timestamp: November 08, 2024, 04:20:08 am
content: I got my parts. It is now possible to attempt this experimentI did not realize it might need a heat sink. I think I have a spare over sized double sided TO220 heat sink some where.

author: coppercone2
author_rank: Super Contributor
timestamp: November 08, 2024, 05:06:02 am
content: arrrrrghhhhhFor 1 miliamp of output power at 250V, the input current is 0.765mA, with no components other then 2 transistorsWith another pair of transistors its 0.769mA (the HFE was 21 on both of them on the little DCA75 meter, for whatever its worth)mirror is a bit crooked23.5% error. But thats with nearly a short circuit load impedance. I am too lazy to try to hook up resistors to it right nowThis was just a power supply and the current source and a dmm (the Dmm internal shunt is the load resistor)it looks like it needs all that other jibba jabbai mean it does like adjust it though, proportionally when you turn the knobs, i think thats a good start that the transistor can actually block the current flow

author: coppercone2
author_rank: Super Contributor
timestamp: November 08, 2024, 06:13:21 am
content: I found a resistor thingywow, on 1 megaohm load, it is within 5.6%When I switch 1M to 5.0 ohms (five ohm) the current changes by only 1 microohm. that seems linear to me!I need to clean up the bench and try it with real HV. Like totally clean it up. I can tell 265V is the problem (lambda psu) for getting high current through those big resistors.I know if the bench is not spotless something bad will happen at 1kV (the one serious piece of advice I give here)I also need to setup a safe resistor holder (I don't trust that chinese gadget for higher voltages)So it does not like nearly dead shorts (DMM shunt) but it seems to be OK as long it has a few ohms.the 34401A has a 5 ohm shunt for the 10mA range. So this circuit might need at least 10 ohms to really function properly for the load.I think that might be good enough for finding a shady resistor !Unless I had the DMM hooked up low side for the first test by accident, I don't know, long day.the results so far seem pretty wild to me!Glad I made the 250uA range on my 6181CI wonder how good it will get if I add the resistors/more transistorsAlright, I think I will try to add the emitter resistors and test it tommorow. If it works I think I will work on packaging it up into a module, leaving well alone. Then all the parts there are very robust for some crap you plug into high voltage rather then trying to cram low voltage transistors in there. I have a feeling its strong right now. I don't recall exactly what but I know the transistors have more complicated parameters eventually and there might be unforeseen consequences from making this have too many parts. I think they only don't add the resistors if it has to be mad cheap or low voltage on a matched chip or modular for a design or have some special process requirement.

author: coppercone2
author_rank: Super Contributor
timestamp: November 08, 2024, 05:59:47 pm
content: 1k emitter resistors make it betterI over stressed the transistors to see what happens. At 60mA @ 265 V on like a 10 ohm load, it did still appear to work, but the absolute maximum is 10mA and 30mA pulse (for 100uS). Afterwards the steady state error increased by 2% and I thought the meter was being a bit drifty and the 'load dependance' of the circuit seemed to change more when I dial different resistors by a few percentI got rid of those transistors but so far I think that is a good sign that it does 600% overload with 265V for like a few seconds and it just looks a bit drifty. good circuit. They do measure the same though on the tester after overload, so I don't know how the damage manifests itself.And it did not wanna go above 66mA for some reason.Does anyone know specifically what is damaged in the 2SC transistor when you pass that much overload current through it (60mA for at least a few seconds)? And why does it cap out at 60mA?

author: coppercone2
author_rank: Super Contributor
timestamp: November 09, 2024, 05:07:56 am
content: I tried to burn another one out, this one I got up to 100mAIt looks like a similar 3% increase in mirror error.I wonder what would happen if I did the same test on MOSFETS lolCould they take it with some damage or would it just totally break, with proportionally the same overload to their ratings in this mirror arrangement.

author: coppercone2
author_rank: Super Contributor
timestamp: November 10, 2024, 03:56:44 am
content: alright PCBWIZ, I tried your circuit with 1 high voltage bJT and the matched pair (MAT12)It works. For a 1.0 setting on the current source, I get 0.951 output. Rock stable when I change resistance of the DUT from 1 mega ohm to 10 ohms. with the power supply set to 262 volts.The emitter resistors are 1kOhm metal oxide type, and I don't have the 'balance' resistor there yet.Not sure if its too much better then the circuit with 2x 2sc high voltage transistors performance wise. At least when its doing nothing.I got a 1 megaohm pot from a old keithley, the long one with a insulating neck for high voltages. I will wire that across one of the resistors and see what happensand the potentiometer needed to crank it up to get 1:1 ratio, is something like 11kOhms. I thought it would be alot more.Your circuits all have 50-300k.I need to attach it on some nicer wire (its very fragile in dead bug form) and try to lock it in exactly.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: November 10, 2024, 05:24:37 am
content: Quote from: coppercone2 on November 10, 2024, 03:56:44 amIn LTspice I used the lowest gain models at HV, but your devices are lower gain again, so that's expected to give lower trim gain = 1 values.

author: coppercone2
author_rank: Super Contributor
timestamp: November 10, 2024, 05:33:25 am
content: Ok, its actually 25.3 Kohms, I changed it to a 50k pot to dial in on it (1mega is very hard to adjust).the HFE of the mat12 is 1300 on the little meter lol, but who knows what is really going onI will add that resistor in non potentiometer form and probe some voltages at various nodes, and then maybe try it with the real HV supplyI adjusted the potentiometer at 1mA, because it seems like a mid range between low current tests for not daamging stuff like insulation and the 10mA full scale for stressing things, and because 1 megaohm will pass something like 1mA of current maybe, I think tailoring it to the higher currents is not nearly as useful for precision accuracy.I am trying to figure out how to mechanically shore up the circuit. That Mat12 dangling around is kinda shady.

author: coppercone2
author_rank: Super Contributor
timestamp: November 10, 2024, 05:39:20 am
content: also do you have any recommendation where to tie in the mat 12 body / substrate ? it says you can leave it floating or tie it to the lowest point. kinda scared with HV around

author: coppercone2
author_rank: Super Contributor
timestamp: November 10, 2024, 10:23:54 pm
content: And I am wondering what else I can do to trick out a current mirror that is gonna go into a little box. I thought to put some decoupling capacitors on it. Maybe 10nF?or maybe even LC ?I found a box that will fit it nicely to make a bench top 'module'I thought maybe if I put a bit more thought into it, it might be useful for other things in the future that require stable constant current HV.And putting a TVS diode on the control input (current source input) seems like good idea. I think I even have some special fuses rated at 10mA to protect it, though I don't recall their voltagveIs there anything to watch out for? Now that its a MAT12 I don't want it to explode lolA capacitor could store charge though. I don't really know off the top of my head when it get severely unpleasant to touch a cap. 1nF @ 1200V seems reasonably small. 10nF maybe is getting mean. Human body model is like 150pF IIRC, at 25kV.. I think that might be one of those shocks that makes you recoil and makes a little snap? So I think 1nF @ 1200V might be acceptable and also maybe get rid of a little noise? It will have to be a bunch of cables strewn out on a bench, making it connect into the front of the equipment is looking cumbersomeI also thought to put maybe a 100 ohm resistor in series with the current control, even though its a current source, to maybe bolster the ability of the 1nF capacitor to filter.

author: coppercone2
author_rank: Super Contributor
timestamp: November 11, 2024, 01:16:18 am
content: alright I got the high voltage supply out, I am glad to be getting away from all those digital displays in this project, good vacuum tube circuit instead.Only problem is I see the 34401A does not want more then 500V, from a grounded supply (its built with earth ground)It seems to work nicely at 500V. I guess I will need to find the fluke for the higher voltage test. I forgot the meters can't take this kind of potential.

author: coppercone2
author_rank: Super Contributor
timestamp: November 11, 2024, 02:02:51 am
content: looks like it works at 1000VDC, no change in 50uA current when I switch it from 500 all the way to 1000, but now it needs to be put into a box with good connectors instead of grabber hooks and stuff working at way too high a potential. using this setup for more then one verification is asking for trouble.https://imgur.com/a/59hZhJ8

author: coppercone2
author_rank: Super Contributor
timestamp: November 11, 2024, 05:32:54 am
content: if anyone knows of a higher voltage BJT... I will probobly try it.But I did also get a shit load of 2sc's for experimenting with 'ladder mirrors' . I am happy that they appear at least somewhat hard to really 'break' in a classical senseshame though, with the age of this part, I figured we would be at 30kV "enhanced package to-220" transistors with teflon pants

author: coppercone2
author_rank: Super Contributor
timestamp: November 11, 2024, 06:02:54 am
content: and I would be happy to try any 2SC ladder type circuits that anyone wants to come up with, I might even have a crappy 5kV power source from some air purifier, maybeThe AOE has something, I think its derived from thisI spent some time looking at AOE circuit, and I am not sure if you need to do that with BJT. It looks like you would actually need to test the configurations to look for the bumps they describe.

author: coppercone2
author_rank: Super Contributor
timestamp: November 12, 2024, 03:19:56 am
content: this might be a reason to buy a decade or two of E values of some high voltage resistors for experimenting on.And my idea for securing the transistor is now to solder a solid wire to the top of the can and solder it to the negative banana terminal on the chassis, it should stop it dangling like it is in the picture, or just secure it to a nylon bolt if it is better ungrounded.This might be a good technique for complex dead bug circuits, to solder a thicker wire to the top of a can and secure it to a insulating post. Though I guess it acts like a bit of an antenna.Lol, or to solder a loop to the top of it, and 'bolt' it to a long, possibly heat-bended nylon or other bolt LOL. All the slow mechanical BS is getting on my nerves. There has to be a way other then trying to make god damn circuit boards for everything. Though, as far as easy to engineer, soldering loops to the top of transistors and bending plastic bolts into shape might not be such a terrible choice.I am gonna get some extra long 8-32 nylon threaded rod to find out if it can work! I don't see many easy techniques for high voltage durable prototyping. If you have a laser cutter I guess you can make acrylic cuttings, but this might just work.