Both of these drivers use open-collector outputs, so the output voltage you measure is determined by the anode supply voltage, nixie-tube voltage drop, and the voltage-drop across the anode resistor (due to leakage of the driver IC). It's indirectly affected by the IC.
I suspect the "high" output voltage you see is caused by lower leakage of the driver IC. You can confirm this by measuring the leakage current directly with a current meter, but it's much easier to measure the voltage across the anode resistor and calculate the current. When the driver IC has lower leakage current, the off-state (output high) voltage will be higher versus devices with higher leakage current. One characteristic of NPN transistors that is not commonly known is that running the collector-emitter junction higher than spec does not destroy the device like it does with MOSFETs (bipolar transistors do not have vulnerable oxide layers). However, like a zener diode, you have to limit the current at higher voltage otherwise the junction will overheat and that will destroy the device. Nice find. I vaguely recall hearing about the 8T01 many years ago, but not the H158. On Wednesday, January 15, 2025 at 1:19:14 AM UTC-8 Leroy Jones wrote: > Just ran across this H158 obscure nixie driver IC. It has binary inputs > and 1-of-10 nixie outputs. It is from a logic family known as HLL (high > level logic). It operates at a Vcc > of 10.8 to 20 volts. Ceramic milspec DIP package. It has the > identical pinout > as the standard 5 volt 8T01 driver IC. > > Anyone ever hear of these H158 driver ICs or know anything about them? > Same for 8T01. Just got in some 8T01 ICs to test. They work very well > but they > do have quite high "off" cathode voltages at certain times. I see an > "off" cathode > being anywhere from 50 volts to 110 volts above ground. > > According to datasheet it can handle up to 68 volts. But these were all > designed to > operate the tube cathodes directly with no other parts. > > 100+ volts seems a bit high, but it all seems to work ok. What is up > with that high voltage? > > -- 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 view this discussion, visit https://groups.google.com/d/msgid/neonixie-l/1939a7be-312a-439b-8d1e-f6f60fd8fb73n%40googlegroups.com.
