To drive a nixie tube, you first need to connect its anode pin to 170 VDC via an anode resistor (8200Ω recommended value). To light up the desired digit, it is necessary to bring its pin to the ground (0 VDC), this can be done in many ways – connecting by wire directly, using discrete transistors (refer to [1]), or chips which are designed for this purpose (e.g. Microchip HV5622).
High voltage power supply
As a source of high voltage, I recommend a step-up converter that creates 170VDC from low voltage (typically 5-12VDC). As an example, I can name a few modules I have experience with, they are all very well designed, efficient and reliable.
1364 – SmartNixie HVPS-H by Taylor Electronics – small high voltage power supply, variable high voltage output (150-200 VDC). It can drive up to 6 of our R|Z568M nixie tubes. Several external parts are needed to set it up.
Simple way
This is a simple driving circuit using a discrete high voltage transistor MPSA42. To light up a digit, connect the base of the transistor to 5V. To turn it off, leave the base at 0V. There is just one transistor shown in the circuit (for digit “4”), each digit must have a transistor connected in a similar way – there will be 10 transistors in total.
The advantage of this circuit is its simplicity and low demands on space on the PCB. The disadvantage is that when driving the nixie tube this way, the individual digits have small differences in brightness (intensity of the light per square unit of the cathode). This also means that the sputtering on the individual digits have different rates which can cause faster development of cathode poisoning on rarely used digits. If you like to do it properly, I recommend the “Proper way” circuit.
The maximum heat dissipated on the anode resistor is around 300 mW, we recommend using resistors in the 2512 package which is usually rated for 1000 mW.
Proper way
This is a driving circuit using a discrete high voltage transistor MPSA42 and cathode resistors. These resistors slightly reduce the effect of cathode poisoning by equalizing the current of individual digits. To light up a digit, connect the base of the transistor to 5V. To turn it off, leave the base at 0V. There is just one transistor shown in the circuit (for digit “4”). Each digit must have a transistor connected in a similar way – there will be 10 transistors in total.
The maximum heat dissipated on the resistors is around 200 mW, we recommend using resistors in the 1206 package which is usually rated for 250 mW.
The anode resistor is 4k7 Ω.
Cathode resistors values:
| Digit | Resistor Value |
|---|---|
| 0 | 1k2 Ω |
| 1 | 4k7 Ω |
| 2 | 1k1 Ω |
| 3 | 1k5 Ω |
| 4 | 3k3 Ω |
| 5 | 1k1 Ω |
| 6 | 1k1 Ω |
| 7 | 3k6 Ω |
| 8 | 0R Ω |
| 9 | 1k Ω |
Further reading about driving nixie tubes:
Driving Nixie With Discrete Transistors
Driving Nixie Tubes by Threeneuron