Shep,
There are two polarities of transistors, NPN and PNP. NPN requires the base to
always be 0.6V more positive than the emitter, and PNP requires the base to be
0.6V more negative than the emitter.
The anode must be controlled from the 180V point, not from the 0V point. The
most straight-forward way to do this is with an NPN transistor whose emitter is
connected to 180V. The base is controlled by a high voltage NPN transistor
through a resistive divider, to allow the on/off command to be sent across the
180V 'space'.
An example of a multiplexed anode drive circuit that works is shown in my old
Nixie clocks... page 17 has the schematic diagram.
http://www.cathodecorner.com/nc620akitman.pdf
On 3/29/2016 2:51 PM, Asstroman wrote:
Hi gregebert!
What do you mean when you say the NPN transistors will only drive out
4.3V? The transistor I was planning on using was the MPSA42 which is a high
voltage-power transistor. The datasheet says that Vce is about 0.5V, so
disregarding the anode resistor, if I were to drive the Nixies with 170V supply,
shouldn't the anode see about 165.5V. Also, using an NPN I thought that
the 74HC238 would be sourcing the current rather than sinking it. Am I incorrect
in this thinking? Thanks again for your reply and helping me to understand this
stuff.
Shep
--
David Forbes, Tucson, AZ
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