i want to drive my nixie clock with mpsa42, but i am confused about wiring diagram. I found one with Base resistor and one without it. From some sources i found that mpsa42, is digital BJT, but from its datasheet it´s not very clear for me Link to Datasheet of mpsa42: https://cz.mouser.com/datasheet/2/258/MPSA42_7eMPSA43(TO-92)-1626582.pdf enter image description here

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Edit: i wanted to drive it like this: enter image description here


The MPSA-42 is NOT a "digital" transistor in the sense that that is normally meant.
It does not include a base resistor on the package - this must be provided externally if required.

A base drive resistor will be required in all common emitter circuits.

Please provide a copy of your circuit and / or a link to the circuit you intend to use. Usually the MPSA42 emitter will be grounded, the base will be driven via a resistor and collector will connect to a positive high voltage load.


Any BJT with a base drive resistor becomes a "digital transistor".
Any FET is a "digital transistor"

Here is a Digikey list of FETS with Vds >= 300V in 10 quantity.
The lowest cost AO3162 is rated at 600CV at 34 mA for $US0.28 in 10 quantity.
The IDP50R3KOCEA... is rated at 500V at 1.7A and cost $US0.35 in 10 quantity

  • \$\begingroup\$ Thank you for quick response, can you suggest me some cheap digital BJT or mosfet that i can drive from cmos logic and have breakdown voltage over 250mA? \$\endgroup\$ – Jakub Prochazka May 16 '20 at 12:38
  • \$\begingroup\$ @JakubProchazka nobody can suggest what you ask for because it is illogical. \$\endgroup\$ – Andy aka May 16 '20 at 13:11
  • \$\begingroup\$ Thank you for your reponse, I mean 250V. \$\endgroup\$ – Jakub Prochazka May 16 '20 at 13:16
  • \$\begingroup\$ @JakubProchazka See addition to my answer \$\endgroup\$ – Russell McMahon May 17 '20 at 0:38

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