HV Generator open output voltage – limited internally to under 200V. The red LED lit up to indicate the voltage limit has reached.

The Pocket High Voltage Generator that I made a few weeks ago proved to be a very handy tool. I have been testing Zener diodes very often since I use many Zeners in 12V to 91V range.

However I wanted to give it a bit more power so that I can test Nixie tubes clearly – the previous design can only give less than 0.5 mA through most Nixie tubes, some digits don’t lit up completely.

I made some upgrades to the components to give it a modest 2 – 5 mA (depending on the voltage) output. While still keeping the same form factor.

Upgraded HV Generator can comfortably drive Nixie tubes at 1 – 2 mA of current.

Now this circuit has enough oomph to shock you if you accidentally touch the output! Not the dangerous level, but it IS shocking. Perhaps one can use this as an electric Jack-in-the-box…

I’m sharing the PCB design of this project. Which can be purchased or downloaded via OSH Park.

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- There’s an update to this post, including PCB design files. -

There are times you find yourself looking for a relatively high voltage (100V to 200V often in my case) but low current DC power supply. I have zener diodes that are higher than 30V, which makes the lab supply useless, and filament LEDs with forward voltage over 60V. When I need to test them quickly, I used to hook up a simple rectifier circuit to a variable AC power supply (nothing more than a slidac with isolation transformer). While this gets job done, the setup is capable of supplying much too high current (1A or more), so I was always very nervous and extra careful in handling the circuit. All I need is a little HV generator that gives me around 200V DC and only capable of supplying a milliamp or less. Realizing that I do have such design available – one of the Nixie supply circuit – I just decided to put one together to use.

Pocket HV Generator schematics

Quick & dirty build of the tool.

A single AA battery seems to be enough to generate over 200V on the output with no load. But the output quickly lowers when you draw 0.4mA. So it feels pretty safe to handle this casually, and I can only feel a bit of tingling, not electric shock when I touch the output terminals. The tool proved to be quite handy and useful in testing variety of things:

• Zener diodes (zener voltage)
• Switching diodes (reverse breakdown voltage)
• Filament LEDs (forward voltage)
• Regular LEDs (forward voltage – yes it’s ok to use this tool, since it’ll only give less than 1mA even at 2-3V)
• BJTs (breakdown voltages)
• Neon & Nixie tubes (not very bright, but you can tell if one works or not)

Pocket HV Generator testing a zener diode

Pocket HV Generator testing a Nixie tube

This is one of the most useful tools that I’ve made. And it only took a couple of hours to put it together.

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Only part that needed developing was the high voltage power supply. I did not want to use mains AC as the power source, and ideally wanted to use 5V DC so that the clock can be powered from USB.

After a bit of research I found that most of the high voltage power supply designs use boost converter driven by a PWM controller IC such as MC34063. A large MOSFET switching a good size inductor. Those designs looked a bit overkill to me, so I started designing my own from scratch.

Since I’m familiar with transistor based blocking oscillator circuit to boost voltage, I wanted to see if I can use similar circuit. The switching transistor has to withstand the output voltage of 180V so I picked some high voltage transistors and experimented. Turned out that typical high voltage transistors (C-E breakdown of more than 200V) were too wimpy for the purpose, and the simple two transistor circuit that I was using was not capable of very high duty cycle demanded by high input/output voltage ratio (I’d estimate close to 99%).

One way to reduce requirement for the boost converter is to add voltage multiplier at the output. I added a 3 stage Cockcroft–Walton multiplier to a circuit using pretty ordinary (inexpensive) transistors. This circuit was able to provide required voltage and up to around 3 to 4 mA of driving current to medium sized Nixie like IN-12.

While this power supply was not quite powerful enough for larger Nixie tubes, I went ahead and designed a clock circuit to get my feet wet.

First design was a 4 digit clock using ATMEGA328 – I wanted to make the software easy to develop, so I loaded Arduino boot-loader. I also wanted to use the clock as a multipurpose numerical display so I added a V-USB port.

This prototype had some stupid bugs, but the basic functions such as multiplexing worked. I made a revision of this prototype right after.


Here I experimented with a tapped inductor to effectively double the boost converter output voltage and do away with voltage doubler instead of tripler.

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There are many Nixie Clock designs available on the net. They are usually two types; AC main powered clock without MCUs, or low voltage DC powered with MCUs. I prefer low voltage variety because of the safety reasons, as I like exposed PCBAs.

All of the low voltage designs have some kind of high voltage (180V typical) generation circuit – and I noticed that all of the designs that I see use a pretty hefty MOSFET driven by a PWM controller IC. Somewhat complex and not so small. I kept thinking – there has to be a simpler solution.

I’m sure many people reading this are familiar with Joule Thief circuit. It’s a simple blocking oscillator based boost converter. I have done some work with two transistor variation of Joule Thief extensively, and thought I should be able to use that circuit for Nixie power supply.

Looking at the basic circuit I realize that the output voltage is limited by the breakdown voltage (Vceo) of the switching transistor. So I tried testing with high voltage capable transistors. The result was not so good – you can get the voltage, but could not deliver the current Nixies needed.

So I decided to add voltage doubler to the circuit, which looked promising. After many tries with different transistors and voltage doubler or tripler combinations I was able to come up with a supply that can deliver about 7mA of driving current into a medium sized Nixie. The circuit only uses two transistors, a not so big inductor and a few diodes and capacitors. It is much simpler and smaller than all of the Nixie power supply I have come across.

It’s not as strong (only 180V and 7mA driving current as opposed to 200+V with 10+mA) and voltage regulation is not so good. However it’s more than good enough for small to medium sized Nixie tubes. It can also work with input voltage as low as 2.4V when you don’t need much output current (i.e. miniature Nixies like IN-17).

I have designed a couple of Nixie clocks using this power supply. I will follow up with some descriptions of each stage of the designs.

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Color Organ Triple Deluxe II is the return of the classic color organ of the 70′s using LEDs. Color Organ divides sound wave into three bands; low, mid, & high, and lights different color LEDs based on the volume.


Color Organ Triple Deluxe II uses all discrete transistor circuit for authentic “sound to light” function – no ICs, no microcontrollers. Assembly is also very straightforward and beginner friendly.

- See the instructables

- Download the schematics

- Checkout the Laser Cut Acrylic Case

Kit Contents

• 3x 47 ohm
• 6x 150 ohm
• 2x 270 ohm
• 1x 470 ohm
• 2x 1k ohm
• 2x 4.7k ohm
• 4x 10k ohm
• 3x 270k ohm
• 1x 1.2M ohm
• 1x 10k ohm potentiometer
• 1x 4.7nF (0.0047uF)
• 2x 22nF (0.022uF)
• 1x 0.22uF EC
• 1x 1uF EC
• 3x 4.7uF EC
• 1x 10 uF EC 16V or higher
• 1x 47uF EC 16V or higher
• 8x MPS2222A or Equivalent
• 18x LED (6x red, 6x green, and 6x blue)
• 3.5mm Stereo Jack
• DC Power Jack

Notes:
Kit assembly requires basic soldering skills.
You need a 12V DC power supply (AC adapter) (300mA or higher current capacity – such as this one) to operate Color Organ Triple Deluxe II. Use of regulated power supply is recommended, since non-regulated AC adaptors typically produce output voltage much higher than they are rated. (Typical “12V” non-regulated AC adaptors can output about 18V.) If you want to use one of those, make sure to masure the actual output voltage, and only use it if the voltage is lower than 15V. (Try 9V rated ones.)

*** Purchase Here ***

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Just finished this project, and published the instructables.

More info here

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