Hi,
Well, a simple problem. I have a design with all logic at Vdd = 3.3V. I need then to control a number of high side PNP transistors powered from
12V rail. I use currently NPN transistors for that purpose (bases of PNP transistors being connected through resistors to collectors of NPN's).I would like to simplify this and replace all NPN's with one chip of open collector drivers like 74xx07.
The problem is I cant use TTL part as I have VDD only 3.3V, and for CMOS variant the problem is that they are specified for Vout no more than Vdd (they have clamping diodes to Vdd at they output pins).
My question is whether it is OK to use these parts somewhat beyond the recommended conditions, connecting output collectors through resistors to say 12V (to bases of PNP transistors in my case). It seems I am still safe since the diodes will not allow Vout to rise above Vdd +
0.5V which is still within "Absolute maximum ratings" of the part.Is there any better solution?
TIA
-Arkady-