Zitt, The problem is not that it is an open drain or a CMOS (it is a CMOS and I put it as so in my first email). The problem is that the base MPSA42 conected directly to the output effectively shorts the output to ground unless you put some resistance into that base circuit. You say you tried putting a resistor in the base of the transistors to no avail. To avoid unpleasant sudden malfunctions, let the resistors there.
If you suspect a timing problem, try slowing the multiplexing to a very slow rate. That should let you see if there is something wrong with the logic. With no "conversion" the buffers are connected straight to the inputs so you should have no problem testing that part of the circuit manually. > On Thursday, April 4, 2013 7:48:32 PM UTC-3, Zitt wrote: >> >> TI's data sheet says that the 503 is capable of sinking and sourcing >> current: >> http://www.ti.com/lit/gpn/cd4503b >> and the drawing shows N and P transistors in the output. >> >> So the device isn't open drain. >> >> at 5V; the device can sink (low) 2.3mA typical and source 1.9mA typical >> (high). >> Even with a minimum beta of 25 for the kathode drivers; IB would be 80uA >> given a 2mA emitter current. >> >> -- 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/msg/neonixie-l/-/l8ospxhk1nUJ. For more options, visit https://groups.google.com/groups/opt_out.
