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I am new to this forum, heard you guys are great and helpful.

I have been designing a nixie clock recently for my girlfriend's birthday.

The tubes run at 170v and have a current rating of 2.5mA. I want to use a high voltage interface driver chip HV507GP (datasheet in hyperlink) to drive them (sink only) but suspect that it doesn't have enough current sinking capabilities (1mA stated in datasheet at 300V I think?).

Can someone confirm or debunk my suspicion? It will be much appreciated. datasheet for HV507PG

Thank, Hang

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  • \$\begingroup\$ It appears that is for the whole HV supply - not per pin! Did you want 2.5mA all up or per pin? | Emitter (or source) followers would be annoying but doable. Drive line and output run across boaard and drain/collectors via'd under - stagger transistors for packing - quite compact \$\endgroup\$ – Russell McMahon Jun 11 '15 at 15:17
  • \$\begingroup\$ This site has many capable people. The rules on what is on topic can be restrictive on occasions. A complementary site is the "PICLIst" - despite the name it's very wide ranging. Mailing list style - www.piclist.com and follow instructions. (NB - it's not a one or other choice - they are both useful and complement each other). \$\endgroup\$ – Russell McMahon Jun 11 '15 at 15:19
  • \$\begingroup\$ might be worth having a look at what others have used (a lot use the 74141) - you can always add your (low voltage) serial interface to drive them. \$\endgroup\$ – JIm Dearden Jun 11 '15 at 15:57
  • \$\begingroup\$ There's a Russian version of the 74141 floating about too. K155ID1. \$\endgroup\$ – Spehro Pefhany Jun 11 '15 at 17:26
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If I understand the datasheet of the HV507GP well then it can indeed only source or sink less than 1 mA. Note that there is also a resistor in series with the NMOS drain for the HV outputs. It is unclear what the value of this resistor is but for sure it does not help in your case.

This IC is meant for electrostatic applications and that means high voltage but very low currents.

I'm afraid you will have to look for a better suited driver IC.

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I don't see a clear rating, but the high voltage drop (35V max) at only 1mA is not very encouraging. You could run the tubes at lower current but they would not be as bright. For Nixies you only need one active output per tube.

More importantly, perhaps, I think push-pull drive of a Nixie will prove to be disastrous since the gas will ionize between the numeral cathodes and draw all kinds of harmful inter-cathode currents. I think you really want an open collector/open drain driver here. Note the cathode pre-bias voltage range of a typical Nixie with 170V supply.

enter image description here

One possible solution is to use BJTs and ordinary logic. MPSA42/MMBTA42 transistors are cheap and plentiful. You don't actually need the full supply voltage breakdown for the transistors if one numeral is always on, but the 'A42 is rated at 300VDC anyway. Since the current is only a few mA you can use them in common-emitter or common-base configuration depending on whether you want logic inversion or not.

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