# 4000 series logic with TTL inputs?

Is there such a thing as a variant of the 4000 series CMOS logic chips which has TTL compatible inputs?

Something like the 74HCT but for 4000 series.

The reason I ask is that I am looking to switch a number of 12V low current signals from a 3.3V or 5V source (the grids and anodes of a VFD, while the filament is running from a 5V square wave), and 4000 series running at 12V would be ideal for that (e.g., the 4069). However, in all the variants of the 4000 series I have found, the $V_{IH}$ scales with the supply voltage (as is normal with CMOS logic), which at 12V puts it way outside the range of a 5V logic signal, let alone a 3.3V one.

Alternatively, can you suggest a different family of chips? It wants ideally to be usable by novices, since it's going to form part of a tutorial.

• Do I understand you correctly if I say that you want a CMOS inverter (like 4069) running on a 12 V supply but with inputs for 5 V (or 3.3 V) ? In CMOS the $V_{IH}$ and $V_{IL}$ scale with the supply voltage so any logic running at 12 V needs 12 V input signals. You should look at open collector/open drain outputs with a pull up (to 12 V) resistors or a proper levelshifter IC. Dec 21, 2017 at 13:05
• You could simply use transistors or an open collector chip like the ULN2803 which goes up to 50V. Dec 21, 2017 at 13:07
• The 2003/2004/2803/2804 series cannot source current to the output. A pull up resistor might work for that IF IF IF we knew more about the downstream circuits. Schematic? Dec 21, 2017 at 13:25
• There's no real downstream circuit, just a grid or an anode of a VFD. Minimal current (nano amps). OC + pullup may work, actually... Dec 21, 2017 at 13:52
• Yep, OC + pullup works nicely (or would if one of the ULN2803 chips I dug out wasn't dead...). Dec 21, 2017 at 14:46

In the end I opted for ULN2003 chips with 10K pullup resistors. Only tiny currents (nA or even less) are needed for the anodes and grids, so 10K is perfectly fine. As it turned out I really needed around 30V rather than the 12V I was planning to get good brightness from the VDF when multiplexing 1:9, so the ULN2003 was perfect for the job.

Kudos to @oldfart for reminding me of the existence of them.

You can use the hex inverter with Schmitt-trigger inputs 40106 in combination with a level shifting network at the inputs.
The level shifting network should shift the input signal up so both levels go above/below switching levels of the Schmitt trigger. It could be done with a voltage divider (connected to Vdd and the input signal) or with a resistor-diode combination.

At least for the 5V signal it should be doable (typical hysteresis is 2.3V @Vdd=10V and 3.5V @Vdd=15V).

" The reason I ask is that I am looking to switch a number of 12V low current signals from a 3.3V or 5V source (the grids and anodes of a VFD, while the filament is running from a 5V square wave), and 4000 series running at 12V would be ideal for that (e.g., the 4069). However, in all the variants of the 4000 series I have found, the VIH scales with the supply voltage (as is normal with CMOS logic), which at 12V puts it way outside the range of a 5V logic signal, let alone a 3.3V one."

I don't know what you referring to (VFD? varible frequency drive and vacuum tube elements?). But typically to control something like this is a standard transistor circuit. So the ULN200x,ULQ200x series is what you looking for as device (a multichannel current switch). Ive used them in many things, from switching lamps, to driving little stepper motors.

• VFD = Vacuum Fluorescent Display. Grid and Anode need to be given a switched voltage greater than the voltage of the cathode element. Dec 21, 2017 at 16:42
• Then the uln series should be fine for that. lol so many abbreviations out there for electronics... Dec 21, 2017 at 16:47
• I have it working with ULNs and pullup resistors. Fortunately only very tiny currents are needed, so pullups work fine, with the ULNs acting to connect the grid/anode to 0V to turn it off. Dec 21, 2017 at 16:48