Greg, Thanks again for those nuggets of wisdom! I have noticed that about NPN BJTs. In particular, the output side of a 4N35 optocoupler is rated at 35 volts max. However, I have been very successfully using 4N35 optocouplers in a 48 volt system for 20+ years with no issues nor failures. I have noticed that when current is kept extremely low or practically non-existent, that the specified maximum terminal voltage can be exceeded significantly with no problems. I never knew exactly why. Now I know why! Thank you!
On Wednesday, January 15, 2025 at 12:10:12 PM UTC-5 gregebert wrote: > 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/72668bae-06cc-426e-8dfd-cc3badc81e33n%40googlegroups.com.
