# High Voltage Power Supply for Nixie and Valve Tubes

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## Introduction: High Voltage Power Supply for Nixie and Valve Tubes

Since in last years nixies displays attracted my attention so much that I bought many of them, I finally managed to design a good power supply and my nixie clock is on the way... [UPDATE: done! read instructable here)
With this circuit you can test a nixie display, or power a multiplexed nixie clock. The potentiometer lets you change the output voltage to fit different types of displays (you can obtain from 100V to 300V DC). My prototype has been built on a breadboard, but I also made a pcb from the schematic so you can etch your own board and solder the components.

WARNING: this circuit raises the voltage to deadly 300V so you must avoid to touch contacts while working, I'm not kidding, please BE CAREFUL!

## Step 1: The Schematic

To understand the way a circuit can raise voltage from 9V to about 180V I had to make some research in the web, because I'm not so skilled in electronics to design my own circuit. Anyway I merged some information from the most exhaustive sources, and my circuit tries to be simple and efficient, but most of you readers can probably add some revision or advice.
The two best sources, which are must-see, have been arduinix.com (device assembling instructable here) and Threeneuron's Pile o'Poo, and both their circuits are a bit different from mine, since from Arduinix I've taken the NE555 application, and from Threeneuron's the use of a pull-down transistor to improve the efficiency and reduce the mosfet heat. You can also read ian's instructable to better understand working principle and components details. Another source was this document from www.ledsales.com.au.

On Threeneuron's website you also can find informations about the calculations to find the right R36 anode resistance value to limit the current for each type of nixie display. Let's say that 15 Kohm will probably work for 90% of the displays.

I also report the explanation of circuit functioning as -max- wrote in his comment:
An inductor is used to create high voltage kickback. This configuration is often found in boost converters, called that because the boost voltage. It works because one can not change the current flowing through an inductor spontaneously, inductors resist change in current. This means when the MOSFET turns on and passes a current through your inductor, the current flowing though it will steadily rise, "charging" it. It will eventually reach saturation where the magnetic flux can no longer increase and the inductor acts like a short. This is sort of like stretching a rubber band or spring. There is a point where you can no longer pull it tighter (otherwise it will break). Once this point is reached (or often just before it), the transistor turns off, and the inductor is allowed to "snap" back. Remember, the current absolutly cannot change instantaneously. so what happens is when the current is removed, the magnetic field in the inductor created collapses and induces a potential across the inductor. This voltage will slam up to infinity until a current flows between the 2 terminals.
However, in the real world, there is stray capacitance within the inductor as well as outside it, especially if a capacitor is connected. This creates a tank circuit, so the output will actually "ring," it is the equivalent to a bell, tuning fork, spring on a string instrument like guitar, etc. This can be seen on an oscilloscope with the probes connected across the inductor. You will see the ringing and even the initial voltage spike, known as a "transient voltage spike." The diode simply rectifiers this spike and transient so the voltage is DC, although quite a dirty one. (The voltage is all over the place as the inductor oscillates) the capacitor smoothes this out, offering a clean DC high voltage to the nixie tube.

## Step 2: The Components

Some detail regard the components.
L1 is a fixed inductor 100 uH 1A, threeneuron's lists some similar models of it, and they could be a little different in dimensions, so my pcb has space for long and short components.
R17 and R18 should be 1% accuracy metal film resistors, to achieve a better voltage stability.
D1 has to be a ultra-fast 400V diode, as BAV21, UF4004, UF4007, MUR140, or MUR160 (thanks threeneuron's again).

## Step 3: The Pcb

The pcb has been obtained in DipTrace from my schematic. Maybe you can design a better arrangement for components, I didn't etched this board because I'll incorporate the supply circuit in my nixie clock board. There is space for a big heatsink, also if probably you don't need it. In alternative you can lay down the mosfet. On the left you can see the long shape of the inductance alternative. On the lower right you find the Anode and Cathode contacts, where connect the display.
Attached to this step there are schematics, board and the ready-to-print pdf for toner transfer method.

## Step 4: The Breadboard Prototype

Otherwise you obviously can insert components on a breadboard and test the circuit.
To build your breadboard prototype follow the schematic (not the board) and start adding the IC (the NE555 in this case), connect one pin at time, adding components when they're needed, then connect other components between them and to Vin and ground. Double check everything before connecting the circuit. Also check that resistors pins don't touch anything else.

WARNING (again): this circuit raises the voltage to deadly 300V so you must avoid to touch contacts while working, I'm not kidding, please BE CAREFUL!

I used a bigger pot to ease the voltage setting, and I left my circuit working with a nixie for some time (maybe half an hour) to test the heat dissipation, and neither mosfet or inductor were warm at all... so I didn't add the heatsink.

## Step 5: The Glow in the Dark

Here you can see some different nixie displays, the red glow is very fascinating.
IN-1 are unpopular between hobbyists because they have a shorter life and they're not transparent on the side, but I like them, and once solved the life duration problem they will be great in a nixie clock. Ampoule displays as IN-16 or the very expensive IN-18 are nice, but I love more the top-view nixies as IN-4 and IN-12 (russian tubes had been produced further than american ones, so they're cheaper and easier to find). If you want a exhaustive description about many nixies see here.

## Step 6: This Is Only the Beginning

So this is my contribution to anyone wants to build his own nixie clock, or needs a high-voltage power source to light his plasma devices (as in this impressive instructable, or also this other one) or some valve tubes.
Please comment this instructable and help me to improve the design. I'm waiting for some components to finish my clock, so that you will be able to see it very soon, anyway I know that some improvement is certainly needed and V2 of the power supply can born now...
[UPDATE: my clock is completed and published: https://www.instructables.com/id/simple-user-adjustable-DIY-Nixie-Clock/]

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## Questions

The founder of the American Radio Relay League was working on a high voltage circuit within an RF amplifier one day. He had BOTH hands within the enclosure, and he touched the wrong thing with one hand, and he other hand provided a direct path to ground. It stopped hi heart and killed him. His name was Hiram Percy Maxim, the inventor of the Maxim gun, an early form of machine gun (similar in some respects to the Gatling gun.). He was also a skilled electronics and radio man. Perhaps he had a moment of distraction. It only takes a microsecond.

High voltage is extremely dangerous, and if you must work with this stuff, keep one hand in a pocket and do not allow a path to ground through your body. Insulated shoes, gloves, tools, and great caution are the order of the day! Don't work on live circuits either.

13 replies

Oh brother! Just found this old post looking at Nixie clocks, and had to set the record straight. YES, working with high voltage/current is dangerous. NO, H.P. Maxim did not die by electrocution. He died at age 66. falling ill after a trip to California to visit the Lick Observatory in 1936. No, he did not invent the Maxim machine gun. That was Hiram Stevens Maxim in 1883. He did invent the "Maxim Silencer" for firearms in 1908, but HP is most remembered as an American radio pioneer and co-founder of our American Radio Relay League; the ARRL.

High voltage is not dangerous. The danger comes when you add any significant amount of current. Doesn't anyone read any of Tesla's experiments and recreate them anymore?

Tell that to the family of Hiram P. Maxim. Or the hundreds of people who die by accidental electrocution each year.

High voltages can lower the resistance of human skin, and perspiration even more so. "The NIOSH states "Under dry conditions, the resistance offered by the human body may be as high as 100,000 Ohms. Wet or broken skin may drop the body's resistance to 1,000 Ohms," adding that "high-voltage electrical energy quickly breaks down human skin, reducing the human body's resistance to 500 Ohms." - from the page referenced below.

One volt at one amp can kill. 300v at a few milliamperes can kill you.

Tesla worked with high voltage, and had the right equipment, and the brilliant mind that it took to avoid being electrocuted.

I can only say 'bindox' that your assumption is incorrect and NOT supported by scientific and anecdotal evidence. If you choose to do these high voltage projects, I suggested utmost caution. Recklessness in almost any field can kill, electricity can kill quicker.

And of course if you shuffle across an ungrounded carpet and touch a ground, you'll likely experience a 'shock', and it will be extremely low amperage (on the order of about 0.0000001 amps.. It takes only 100mA to stop your heart. If your skin is wet, 120V could be enough to kill you.

All I urge is caution. If you don't use it, expect a possibly foreshortened life.

and look at the section on lethality of electricity.

Without questioning the potential danger of electricity in general I still think that your contempt for 'bindox' comment is not justified.

Bindox statement is absolutely correct and very well supported by scientific and anecdotal evidence. If you rub a balloon on a sweater to make it stick to the ceiling you have a perfect, non lethal real life exampe for very high voltage (several 1000 volts) at almost no current. Alos if your statement was scientifically proven, nobody would be allowed to legally sell AA batteries. They can deliver up to 5 Amps at 1.5 V

Yeah, but as you noted very high voltage has to have almost no current to not be lethal, so I will be very cautious in declaring that voltage doesn't kill...

With a human body's average resistance of 100,000 Ohms with dry skin, a 1.5 volt battery won't do much of anything to a human. We were discussing HIGH voltage, not AA cell voltages. (1.67 VDC fresh out of the package.)

I question ANYONE who states that "high voltage is not dangerous". It is, and in general is not something to mess with without the PROPER CAUTIONS as given by the author of the article, and repeated by him and by myself. I think 'bindox' fails to see the big picture.

I hope 'bindox' never decides to test the limits with high voltage. I've worked with it, and under the wrong conditions, it can kill.

That's all I urge is more caution. I have NO contempt for 'bindox', I merely think he/she fails to take all the data into account. Ignorance is what is the most dangerous thing of all.

And Tesla had a brilliant mind, and surpassed Edison in so many ways, but he never got credit for many things. Edison wanted to use DC as a transmission means for electricity to homes and industry, yet didn't have the foresight to realize that this would require power generation stations EVERYWHERE. Tesla knew that AC was the answer for centralized power distribution and even power grids as we have today.

Tesla's method won out, but Edison buried him under lawsuits and paper, and blocked him at every turn. Had they worked together, imagine the great things that might have come to be!

Obviously high voltage IS dangerous, high current IS dangerous, low resistance in your body IS dangerous... Guys please be careful, always use insulated tools if setting up a pot in a working circuit, but preferably NEVER touch a working circuit where high current or big caps are present, also if battery powered. Also if not working, caps keep high current and they can shock you, you must properly discharge them. If you don't know what a circuit is, don't touch it or use insulation.

Very good and I think all of us who have worked around high voltage concur. I hope no one thought that I was not supporting Adrea in his warning, just trying to add a little more information for educational purposes. Thanks Andrea for a good Instructable!

You're welcome :)

No, apparently not. Tesla was very good and did not get nearly the recognition he should have, IMHO. Tnx for pointing that out.

I would also add to my caution about working on live circuits, be wary of circuits that contain capacitors. Those inside old school TV's & CRTs can hold a lot of electricity that can discharge days or weeks later with lethal results.

"Its not the voltage its the current"- is true but it also ignores the fact that this circuit supplies enough current to kill you. The capacitor used to regulate the voltage does output deadly currents. The question is how long is the pulse width. I am busy so I'm not going to take the time to calculate it but my educated guess would be that it has the possibility to be deadly. It definitely is more dangerous than a taser.

Just to add a little information to the "how dangerous is voltage/amperage argument", a typical 5 mile electric fencer (non-lethal to humans) produces a shock from 7500 volts at around 3 amps (22.5kW). Why it will not kill you, is it is only for a duration of about 10 microseconds (0.00001 seconds). The key to how lethal a shock is comes from the total Joules involved. A common 5 mile fencer produces around .25 joules.
A stick welder on the other hand often operates on fairly low voltage (24 volts is typical) at 30-200amps. 100amps is an average weld setting which happens to be a similar wattage (24kW) to the fencer. Difference is that the welder can deliver it until the circuit is broken. In conclusion Volts*Amps*Time is key to whether it will tingle or kill! Obviously safety, education, and common sense is key when working with anything electric.

Hi, I built your circuit on breadboard and it is working fine, but only on no load condition. Powering it from 9V battery I can adjust output voltage between 95-250V. I am setting it up on 180 V but since i connect one IN-4 tube, voltage dropping to around 90V. Nixie glow up and start dimming slowly until extinguish completely. MOSFET get hot in just couples of seconds. It takes time until circuit gets recover.

I inspect all connections, check MOSFET and BJTs and diodes, and they are work correctly, I mean there are no any short or open circuits faults. I should mention I change BYT01 with UF4007, BC547 with BC547C and 1N914 with 2N5401. Maybe someone know a reason of this malfunction?

4 replies

Try to use components I chose. 1N914 has a low maximum voltage, for example. search datasheet in Google, you'll find informations about substitutes. Also duty cicle is very important. This circuit works at very high frequency..

Forget to mention, it work flawless when supplied by PSU.

Components I used are substitutes. After all i decided to forget about making it cordless. It will lay on shelf all the time, so what for ;)

I realised that this problem occur only when I am connected to the battery. When using bench power supply nixies work fine. Since I want it to make battery powered clock it is a serious problem.

what current does the 9v power supply need?