Electronics > Projects, Designs, and Technical Stuff
ne555 nixie power supply not working
<< < (3/4) > >>
Buriedcode:
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.html  In 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..
spec:

--- Quote from: Buriedcode on November 03, 2018, 11:06:10 pm ---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.

--- End quote ---
No 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.
malagas_on_fire:
Well here are one video from DiodeGoneWild to guide the user about Switching power supplies:

https://youtu.be/3ySlJ99OSN4

Search 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.


Boschi:
@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 pm ---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.

--- End quote ---

i know, i was just expecting a bjt to be fast enough, next time i should run some math before tring  :-X

also, 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?
Buriedcode:

--- Quote from: Boschi on November 04, 2018, 03:25:53 pm ---@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)?

--- End quote ---

What 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 pm ---i know, i was just expecting a bjt to be fast enough, next time i should run some math before tring  :-X

--- End quote ---

Speed 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 pm ---also, 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?

--- End quote ---

Saturation 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, please read that 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).
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod