Another important fact about Nixie tube cathodes: turning on one cathode by pulling it to zero volts causes it to steer all the available current away from the other cathodes, causing them to be dark. This is why you only need a 50V switch on each cathode. The caveat is that if no cathodes are pulled to zero volts, then there will be leakage current flowing through the tube that will destroy a 50V transistor. This is why I used the TD62083 with its set of commutation diodes, and connected the diode common anode pin to a 50V source in my Nixie watch circuit. It's also why I made the blanking mode that drops the anode voltage to 100V, so that the cathodes all remain dark when blanked.
On Wed, Mar 6, 2019, 7:57 AM gregebert <[email protected]> wrote: > The required voltage rating of a cathode driver has been debated in this > forum a few times. There are 2 opinions that I know of > > - The driver needs to be rated at the full anode-supply voltage > - The driver only needs to be rated at (Anode_supply_voltage - > Voltage_drop_across_nixie_tube) > > > Based on my knowledge of semiconductor physics, it's fine to use a bipolar > (NPN) cathode driver that is rated at a lower voltage than the anode supply > because the breakdown mechanism is non-destructive as long as the current > is limited. When an NPN is off, presumably when it's base terminal is > grounded (NOT open...), there will not be any current gain from collector > leakage current, so it will stay off. I suspect an OPEN base could result > in some visible glow, depending upon the collector leakage current Ico. > This is why legacy drivers like the K155 or 7441 can drive a nixie that > requires about 160V even though the IC itself can handle only 50 V. > > If you are using a MOSFET as your segment driver, which is typical in > IC's, then you need to use a driver rated at the full anode supply voltage > because a MOSFET's construction is sensitive to excess voltage (oxide > breakdown) as well as current. Long-term overstress of the oxide will cause > reliability problems and lead to failure. > > > -- > You received this message because you are subscribed to the Google Groups > "neonixie-l" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > To view this discussion on the web, visit > https://groups.google.com/d/msgid/neonixie-l/c0c015b5-15e9-4387-b7f7-911193e174a4%40googlegroups.com > <https://groups.google.com/d/msgid/neonixie-l/c0c015b5-15e9-4387-b7f7-911193e174a4%40googlegroups.com?utm_medium=email&utm_source=footer> > . > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/CAPbqtve77G0UfxxoBaoi1JdXgcBR7fW%2BTYZV7K0OTmSK%2B_oQrA%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
