How to drive the cathodes of nixie tubes?

To control a nixie tube and display its characters, the desired cathode must be tied to a ground potential. This will create the glowing discharge on the connected cathode inside the tube. For achieving this, there are multiple options. This article will present the most common and will rate them.

Information and Rating:

The driving circuits in this article are rated with the following points to give a fast and easy overwiev about the showed circuit. All ratings are based on a simple 6-digits nixie clock with number 0-9 (60 cathodes total), no DP or colon separators. Also the values are calculated for a direct-drive system, not a multiplex system!

• Difficulty: Level of skill to achive a working driving circuit (hard and software).
• Price: Average Cost to drive 6 nixie tubes (without the tubes).
• Availability: Where the componentes can be bought.
• PCB-Pads: Number of all pcb pads which result in solder-joints that have to be made!
• Control-Pins: Number of pins that are neccessary to send control signals to the drivers
• Discrete Drive: The driver circuit can be used without a microcontroller and can be used with standart logic family IC's

In a time where nixie tubes where a common electronics product, there was also a need for a appropiate driver. A BDC-Input to decimal decoder with high voltage output, the "7441" or "74141" with the corresponding manufacturer code (SN74141,DM74141,NTE74141 and following), is the most common driver. The difference of the 7441 and 74141 are only on the BCD-Input range, but both models operate the same way. Of course, there is also a russian models that operate the same way, these are the "K155D1" and "KM155ID1". Today, these IC's are only available on auction platforms or surplus electronic stores. The IC are easy to use, can be used with or without a microcontroller and are mostly fair-priced. Plenty of circuits and resources can be found online. 6 IC's are needed for 6 Tubes, resulting in 24 Control pins (6x 4bit-BCD). For the use with a microcontroller a port-expander is recommended.The IC's come in a DIP-16 package (plastic or ceramic) and there are a few rare "flat-dip" versions of the russian K155ID1

Even today, some applications like special printing devices create a need for driver IC with high voltage outputs. The company Supertex (now Microchip) is a manufacturer of such special IC's. A few ICs of their HV-Series can perfectly drive nixie tubes and provide a space efficient and modern solution. The mayority of these IC's come with 32 Outputs that can sink volates from upto 220V to up to 300V, and are mainly just high-voltage shift register that work (and can be chained) the same way as low-voltage shift registers (595 type). The HV5122/HV5222 are the cheapest 32-bit types and can operate up to 225V. A micrcontroller is neccessary to operate this drivers, since a clock and data line must be provided. Coding the 64-bit shift (6 tubes) and the soldering of PLCC SMD packages require advanced skill in hard and software. The HV5222/HV5122 is availiable at the microchip store and at electronic suppliers (Digikey,Mouser).

Some darlington transistor arrays can sink voltages up to 50V, which is not enough to survive nixie voltages, but by clamping the voltage a driving circuit can be achieved.One of these drivers is the UL2003. This array has diodes from each output to a common pin. This common pin can be connected to ground via a zener-diode to prevent the array from destruction by over voltage. The IC is broadly available at electronic suppliers and auction sites. There also may be alot of similar devices that can do the same. The UL2003 comes in a 16-DIP or SOIC package but only has 7 ouputs. To drive six tubes, there are nine IC's needed, resulting in 63 control pins, since each ouput needs a seperate input. The UL2003 can be used with or without a microcontroller and plenty circuits and sample codes are available.

One possibility is to use a transistor or mosfet for each cathode,and then send a control signal to the corresponding mosfet or transistor. This can be done by a microcontroller or discrete logic, but requires 60 Mosfets or Transistors. Most Transistors need also a base resistor to prevent damage. This circuit is not recommend for nixie clocks, it only should be considered when only a few cathodes need do be driven (like +/- tubes) or for colon separator neon bulbs, or in some cases for starter-projects or testing