Why not just use a totem-pole pre-driver for the MOSFET ? BTW, this touches on a challenge when designing HV drivers, whether they are for DC-DC converters or driving cathodes. Most high-voltage NMOS devices (~400V) need 5-6 volts for solid gate turn-on, yet logic-levels on most micro-controllers and FPGAs are only 1.2 to 3.3volts. That leaves a few options:
1. Use high-voltage logic, such as 4000-series CMOS, to drive HV NMOS. My first nixie clock does this. 2. Use NPN drivers; you can easily design constant-current drivers running from 3.3V. I've used surface-mount devices with 2 NPNs inside, and they are rated at 250V. 3. Use a level-shifter between your logic and the driver. I'm doing this on my current design with a HV5530. 4. Find a device with a low-voltage gate. Good luck on this; most logic-levels NMOS devices only handle 60V or less. If you also want low Rds (necessary for DC-DC converters), you have even fewer options. 5. Pull-up resistor. Ugghhh... It will work, but you will burn more power. Could be dangerous for a DC-DC converter if the logic/software turning off the gate goes haywire, which would lead to large current/burnout. I advise against relying upon the voltage-drop of the nixie tube to protect the driver, though this is commonly done with designs using the 74141. I always select my driver to handle the maximum-possible anode supply, and add margin above that. I've never had a fried driver, ghosting, etc. Parasitic capacitance and leakage can stress drivers above their maximum ratings, which will lead to premature 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 an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/4f0cd943-0b8b-432b-b948-d9bb96de5654%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
