On 5/21/14 8:25 AM, [email protected] wrote:
Leakage current ? I've seen past designs that use drivers with a
breakdown-voltage-rating lower than the high-voltage supply. I always use
drivers rated at or above the anode supply voltage, even though there are
reasonable arguments for relying on the voltage-drop of the tube to reduce
the voltage seen by the driver.
I don't see why that is necessary. Neither did National Semiconductor.
The 7441A driver chip contains 70V transistors; it relies on one output
always being "on" to ensure that the breakdown voltage isn't exceeded.
Once the neon ionizes, the voltage on the other cathodes is much lower.
That said, the TI SN74141 was redesigned with 55V Zener diodes on each
output to allow blanking. However, blanking requires that the anode
voltage be lowered, or an indistinct orange blob will appear in the
tube. But the anode transistors don't have to swing the entire anode
voltage either. They just have to make it low enough to not ionize -
about 100V.
I've sold a boatload of Nixie watches that use a Toshiba integrated 50V
Darlington driver. They work just fine. (I put a 50V Zener-reglated
supply on the commutator diode pin.)
--
David Forbes, Tucson AZ
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