# Turning on/off MOSFET using 4000 series CMOS

I intend to use 4000 series CMOS running at 12V to turn on some power MOSFETs (SUM55P06 and IRF2903) handling 8A at 12V.

However, the arrangement of logic gates I need to simplify the driving s/w will produce a race hazard when switching between states, of around 250ns. Can I ignore that? In other words, is the effective switching frequency of the MOSFETs driven from a 4000 much longer than that? I will be driving the MOSFETs around 1kHz

The relevant part of the circuit is shown below

• Your question isn't really clear to me, you might want to add a schematic showing where the race condition occurs and what effect you're worried about. – John D Mar 22 '17 at 14:21
• @JohnD I suppose the question boils down to how fast a (say) CD40106 at 12V can turn on/off one of those MOSFETs – Dirk Bruere Mar 22 '17 at 14:36
• this not how full power bridges are designed, so as shown will not be reliable. the race hazard or "shoot-thru" is a fundamental issue in CMOS design. You cannot blindly go from a CMOS driver with ~150 +/-50% Ohm RdsOn to drivers with 2.4mΩ because Ciss rises with RdsOn and this rise time of gate charge depletion affects the race or the rate of change of turning on or off . Your driver RdsOn ratio is 150/2.4m=62500 and from what I have seen tight control can be achieved with 200:1 with carefully matched drivers for Vgs curves with <1us deadband, – Sunnyskyguy EE75 Mar 22 '17 at 15:04
• That requires a detailed worst case tolerance analysis of all the above variables. But consider 1 variable, CMOS RdsOn ~150 Ω (AFAIK) @12V(e.g. Vol/Iol) and IRF2903Z Ciss = 6320 pf Thus RC= 1us . Thus deadtime design must be >>1us – Sunnyskyguy EE75 Mar 22 '17 at 17:22
• more details google.ca/search?q=ESR/…* – Sunnyskyguy EE75 Mar 22 '17 at 17:29