ne555 nixie power supply not working - Page 1
Forum section: electronics / projects

author: Boschi
author_rank: Regular Contributor
timestamp: November 03, 2018, 11:49:04 am
content: so, i have a few days off uni and i want to finally use some nixie that i have laying around for quite sometime. first thing first: a power supply.i tryed to use all parts that i had laying around, so i used this schematic with a few changes:https://www.ledsales.com.au/kits/nixie_supply.pdfthe only changes that i did was to use a apt13003sztr instead of the irf740 and add a resistor of around 100 ohm in order to limit the base current, but is not working.the yellow trace is the pin 3 of the 555, while the purple one is between the transistor, the coil and the diode (also, i detached the hv output capacitor after the diode in order to see more clearly what is going on on the output side).any suggestion about what is going wrong?

author: malagas_on_fire
author_rank: Frequent Contributor
timestamp: November 03, 2018, 11:56:01 am
content: Well i would recomend first check the connections within the schematic and instead of drive directly the mosfet should be using a 1k to 10K resistor to drop the voltage a little bit on the gate since 555 and mosfet share the same voltage rail , thus the voltage in the gate must be lower than the source.

author: Boschi
author_rank: Regular Contributor
timestamp: November 03, 2018, 12:36:31 pm
content: the apt13003sztr is a NPN, i didnt specify it clearly before.also, im not concerned about the connections because the ne555 is oscillating, the problem is in the output stage and i already checked there.

author: spec
author_rank: Frequent Contributor
timestamp: November 03, 2018, 01:26:18 pm
content: + BoschiNeat, nixi tube power supply.Can you explain what exactly is happening when the circuit is fully wired up with the high voltage capacitor fitted?The first thing to do is fit a low loss capacitor between the power supply pins of the 555: 1uF would be good.It is always wise to check the power lines with a scope, to ensure they are the correct voltage and free from drop outs.Were the only changes to substitute the IRF740 for an APT130035, or are there any other changes?The peak current into the 100uH inductor at a switching frequency of 45kHz, and a voltage of 9V, is around 1A and you are asking a lot of the APTI130035 to supply that current (its current gain would only be 5 at the most and you are exceeding the safe operating area I would guess).Also, is the 100uA inductor rated at 1A and is it a high frequency type? Is the inductor rated at 200V, at least?Is the diode a 1A , at least, high speed type, like the UF4004, or is it an ordinary 1N4004?Is the high voltage output capacitor a high frequency type or just an ordinary aluminum electrolytic type?Just some thoughts

author: MasterT
author_rank: Frequent Contributor
timestamp: November 03, 2018, 01:53:40 pm
content: I experimented with nixie boost converter last summer, and came to conclusion: BJT is too Slow and can't replace MOSFET. I tried MJE13003 & 2N5551. You can easy spot slow reaction on a scope, rising edge of the purple line must be 100-300 nanosec right after yellow line falling edge. Not like 1- 5 usec, you may get with BJT. Later I find an explanation to this in DS, look here:Storage Time with Resistive Load ts — — 3 usFall Time with Resistive Load tf — — 0.5 usAnd compare toTurn-off delay time td(off) - 70 - nsFall time tf - 20 - nshttps://www.mouser.ca/ProductDetail/?qs=W0yvOO0ixfFGjdM3IlgsHw%3d%3d- MOSFET I was using. I was able to get 800V out of 5V input, and diodes should be also as fast as mosfet, 20 nsec or better. FR107 or MUR160

author: malagas_on_fire
author_rank: Frequent Contributor
timestamp: November 03, 2018, 02:24:04 pm
content: Quote from: Boschi on November 03, 2018, 12:36:31 pmOpps sorry i skipped the bjt :p Jesus and the original mosfet can't keep that timming. what about high speed mosfets user for smps on freq 1Mhz. Watch also recommended design as a guideline.

author: Boschi
author_rank: Regular Contributor
timestamp: November 03, 2018, 07:39:18 pm
content: Quote from: spec on November 03, 2018, 01:26:18 pmwell, with the output capacitor it doesnt change much (a electrolytic one from a cfl lamp i think), and the capacitor has the same vaweform as the transistor collector, so probably the diodes i used are not suitable (3x1n4148 in series, 8ns rrt, but the peak current is too much for those?)i already added a bypass capacitor to the 555, 1uf ceramicaaand i should have done it before, the supply has a 3v swing (12V nominal). at its lowest is still 9v (enough for the 555) but still too much.yes, just the apt13003. (im planning to use a tl431 as reference but first of all i need to get it working)about the inductor i dont know, its just a bag of common values i bought from china. it seemed big enough to whistand a 1A peak current, but after searching a bit looks a bit too small. how do i know if its saturating?i was just checking the 1n4148 datasheet, repetitive peak current 500ma. i definitely killed them.thoughts im glad to hearQuote from: MasterT on November 03, 2018, 01:53:40 pmthe MJE13003 and the apt13003 looks the same from the datasheet. i think we found the problem *facepalm*.some UF4004 and IRL740 are on their way to me already.just out of curiosity, how do you determine the maximium allowable fall time?ps: the link is broken

author: MasterT
author_rank: Frequent Contributor
timestamp: November 03, 2018, 08:09:14 pm
content: Quote from: Boschi on November 03, 2018, 07:39:18 pmI fixed a link, something with digikey, they don't have this part number at the moment, but you know what parameters to look for.Maximum fall time is just an experimental data, it would vary for type of inductor, transistors capacitance D-S etc.Till you get a new parts, try to improve switching off time with this RC bias re-polarization arrangementhttps://electronics.stackexchange.com/questions/174770/the-base-resistor-of-the-transistor-with-speed-up-capacitor

author: spec
author_rank: Frequent Contributor
timestamp: November 03, 2018, 08:32:23 pm
content: Quote from: Boschi on November 03, 2018, 07:39:18 pmYou really need to sort the power supply outQuote from: Boschi on November 03, 2018, 07:39:18 pmThe inductor is absolutely the most critical component. Advise to get a 2A (intended) upwards inductor suitable for switch mode power supplies working at 100KHz (intended). The inductor also needs a voltage rating of 250V upwards.Quote from: Boschi on November 03, 2018, 07:39:18 pmA 2A upwards, 250V upwards, high speed Schottky diode would be a good choice.

author: malagas_on_fire
author_rank: Frequent Contributor
timestamp: November 03, 2018, 09:06:17 pm
content: Where is a design reference ...with custom part, but the main subject is the topology used:https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=FB1E65179C0EBD83Of course it is courtesy of TI.

author: Buriedcode
author_rank: Super Contributor
timestamp: November 03, 2018, 11:06:10 pm
content: I think this is a lesson you can't just throw random parts at a circuit and hope it works (sometimes it does!). With switching power supplies the most critical components are the inductor, the switch (MOSFET, transistor) and the diode. The output capacitor is what smooths the output of course but one must have a basic understanding of how the circuit works to see what properties of the components are important.If you must insist on using a 555 circuit for a nixie supply (there are much better circuits around) then this is one of the best explanations about that circuit:http://www.dos4ever.com/flyback/flyback.htmlIn fact I think that's where the original circuit is from, although various boosts and bucks based on the 555 have been around for as long as I have.As you have a scope you can measure the inductance and saturation current with the info in the above link. This is extremely handy if you regular build stuff from "junk parts bin" components, whilst it might be a bit of a hassle, you can just go through all the components and make notes about them, like inductance, capacitance, forward voltage etc..

author: spec
author_rank: Frequent Contributor
timestamp: November 04, 2018, 04:50:34 am
content: Quote from: Buriedcode on November 03, 2018, 11:06:10 pmNo reference to the OP- he is just having a bit of fun.But what you say is so true and even for simple circuits that you would think couldn't possibly go wrong, like an emitter follower oscillating for example.There is a danger in thinking that one component is much like another, but nothing could be further from the truth.The other danger is thinking that the nice schematic of your circuit is how the physical circuit is. But, in fact, wires/PCB traces are not perfect conductors and have resistance, capacitance and inductance. There are also parasitic capacitors all over the place. And that is just the start.I found it very hard to believe that at a capacitor turns into an inductor at a sufficiently high frequency.On a particular equipment we had terrible problems with frequency stability of the master clock signal. To short a long story it was found that the traces to the xtal were slightly too long.And finally decoupling. It is difficult to over stress the importance of good decoupling. The trouble is that decoupling does not appear to do anything functional, by just looking at the schematic.

author: malagas_on_fire
author_rank: Frequent Contributor
timestamp: November 04, 2018, 01:26:58 pm
content: Well here are one video from DiodeGoneWild to guide the user about Switching power supplies:https://youtu.be/3ySlJ99OSN4Search for tutorials and try to understand the Step-Up, Step-Down, Inverter topologies, which are usefull to understand and identify the type of SMPS used. The TI simulator has some nice diagrams / design guidelines.

author: Boschi
author_rank: Regular Contributor
timestamp: November 04, 2018, 03:25:53 pm
content: @spec how do you determine the voltage of the inductor? i tryed searching a bit but i didnt find anything really useful, and also, shouldnt the max voltage just be determined by the enameled wire coating (so like around one KV or more)?Quote from: Buriedcode on November 03, 2018, 11:06:10 pmi know, i was just expecting a bjt to be fast enough, next time i should run some math before tringalso, in your link there is a circuit to measure the saturation current, how it works? like, what happens to the inductor when it saturates? it just stop to act as an inductor and instead it becomes more like a short, so when in the picture i see the "knee" (just before the circled spot marked saturatio) thats the saturation current?@malagas_on_fire that video is more about line isolated SMPS, its a bit different i think. i should really watch the mc34063 datasheet and the waveform diagram to understand better whats happening in the circuit.anyway, after googling a bit i found this:https://threeneurons.wordpress.com/nixie-power-supply/i think ill give a shot to this once i get the new components, mainly because it has a better efficiency and i have some mc34063 in the junk bin.do you have any raccomandations? like phisical layout (but at ~20khz it shouldn matter i think) or to sobstitute a component for another.ps: ill swap the bav21 as main diode with a uh4004, and also the components of the active pulldown (pretty jellybean parts right? maybe use a schottky diode?) and instead of using a single 220uH coil ill use 2 100uh coil, in order to avoid saturation. also, rise the feedback resistor to like a megaohm or more, the fb pin need less than 1ua, right?

author: Buriedcode
author_rank: Super Contributor
timestamp: November 04, 2018, 06:37:12 pm
content: Quote from: Boschi on November 04, 2018, 03:25:53 pmWhat do you mean "voltage of the inductor?" Its breakdown voltage (of its insulation) doesn't mean much unless you're making a multi kV supply.Quote from: Boschi on November 04, 2018, 03:25:53 pmSpeed isn't the problem. Saturation voltage is. You can use BJT's in switched mode power supplies (the MC34063 has two internally and is used in thousands, possibly millions of devices), but you've picked one that isn't suited to the task. SImilarly you could find a MOSFET that isn't suited to the task, like the 2N7002 - it isn't always about which type is better, but what component suits the task at hand. You have to ask yourself, "what is this component doing?" and "what would make it better at this task?".Quote from: Boschi on November 04, 2018, 03:25:53 pmSaturation current is when the inductors magnetic field is at maximum so it can't get any bigger, effectively making the inductor a low value resistor.. this causes a sudden increase in current (the "knee in that graph"). But..that webpage provides and explanation with the schematic- otherwise the schematic would be somewhat useless. As I said, pleasereadthat link. It explains how a boost converter works, what properties of the components are critical, and why he selected the components he did. It is why I liked it. It would just be just as useful without the schematics.Some of your questions leads me to believe you don't know how these circuits work. This is a great opportunity to learn. The boost converter is probably the best place to start but it does involve finding a decent explanation of how the circuit works, - alas a LOT of sources on the web are just awful, quite often explained by someone who doesn't understand it themselves (or just copy/pasting schematics and randomly changing part values).

author: Zero999
author_rank: Super Contributor
timestamp: November 04, 2018, 07:49:12 pm
content: I wouldn't use a 555 for this. A blocking oscillator would do a good job and is much easier to make. The only downside is it requires an additional winding on the inductor, but that's fairly easy to add.

author: spec
author_rank: Frequent Contributor
timestamp: November 04, 2018, 08:00:35 pm
content: Quote from: Boschi on November 04, 2018, 03:25:53 pmThe only way to determine the maximum voltage rating of an inductor, AFAIK, is from the part number and manufacturer's name. You can then check the data sheet.Don't think you can go by the thickness of the enamel on the wire, unfortunately.The working voltage of all inductors is a vital part of the inductor's specification, especially in this case where the output voltage is 175V. That means, by definition, that the inductor will have at least that voltage across it's terminals. The relatively high switching frequency of 45KHz encourages voltage breakdown too (compared to 50Hz/60Hz).

author: Boschi
author_rank: Regular Contributor
timestamp: November 04, 2018, 09:35:06 pm
content: @buriedcode you are right, i should have read the page more carefully.to some extent i understand how all this its working, but i still dont fully get how inductor works. i just need to use them more often@spec for now ill use what i have on hand, also, im finding difficult to find the voltge specification of inductors, so as long as its not a problem ill use generic stuff. the schematic with the mc34063 uses a 220uh inductor, so 2x100uh inductor should do the job, this way im stressing them less.