I use the Toshiba TD62083AFN in my Nixie watch as a cathode driver. It sees 50V
between pins on the 0.65mm TSSOP. I take extra care to keep the anode traces
well separated from all the cathode and logic traces on the PC board. I use
.010" (.25mm) trace spacing between cathodes, and .020" (0.5mm) between anode
and other traces. I also arrange the connector pinouts to minimize voltage
between adjacent pins.
A wristwatch is the most difficult Nixie product to do a PC board layout for,
since there is just not much room on the driver PC board. I've shipped over a
thousand watches over 10 years, without a single PC board arc-over problem.
On 4/8/2016 12:22 PM, gregebert wrote:
If you are driving nixie tubes, there actually isn't 300V between pins at the
driver IC. If your supply is 200V, and the typical voltage drop of an IN-18 is
about 140V when illuminated, the actual voltage-difference between pins is about
60V. That calculates to 0.6mm of spacing, which is still a violation for a 0.5mm
pad-pitch (remember, pad-separation is less than pad-pitch due to finite
pad-width).
My guess is that someone seeking regulatory approval/listing would apply
conformal coating, or similar.
Even if you can't meet spacing rules around nixie cathode connections, you
should use extra effort to meet or exceed spacing rules between high- and
low-voltage sections, and also between HV connections that can have high
current, such as filter-caps and mains-connections.
--
David Forbes, Tucson, AZ
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