Favourite chips...

[Nick]

There are so many driver chips available, from the venerable SN74141s and Russian equivalents through the 4017s, 595s SUpertex chips etc.

What are people's favourite driver chips (clockable, serial driven) ?

Nick

[greg...@hotmail.com]

Firstly, I only do direct-drive.

I dont use driver chips. Instead, I use either NPN or NMOS discrete devices, because I can ensure constant-current thru the cathode.

Using a dropping-resistor will result in some current-variation due to the tube's characteristics, or supply voltage variation.

For larger tubes, you may want to tweak the cathode-current. For example, a '1' numeral will require less current than an '8'. This is possible with per-cathode drivers. Basically, the current-limiting resistor is placed between source and ground for an NMOS driver, or emitter and ground for an NPN driver. The resistor provides current-feedback.

NPN Driver. I use this on my neon watch because the supply voltage of 3.7V is too low for high-voltage NMOS devices. To calculate the emitter resistor value, R=(Vsupply-0.7)/current.  If current is in mA, R is in k-ohms. If you want 335uA for a 3.7V supply, then use 8.9K (the recommended current for an SP-151 display). Be aware that most of the heat will be dissipated by the NPN device, not the resistor.

NMOS driver. The topology is similar, but the gate-source threshold voltage has more variation than Vbe for an NPN transistor. I use 12V for my big-clock, and Vgs is around 3.4V. The driver logic runs at 12V, so variations in Vgs have relatively small effect on the cathode current.

[threeneurons]

Currently, 7-Eleven Jalapeño Kettle Style chips:

... Oh, you mean those other kind of chips ...

[Jan Rychter]

On 4 maj 2014, at 18:10, greg...@hotmail.com wrote:

> Firstly, I only do direct-drive.
>
> I dont use driver chips. Instead, I use either NPN or NMOS discrete devices, because I can ensure constant-current thru the cathode.

Which transistors do you use? I'm especially interested in tiny SMD ones. Dropping some hints would be very helpful -- it is difficult to just start searching for semiconductors out there.

--J.

[David Forbes]

I use the Toshiba TD62083AFN for my Nixie watch. Eight 50-volt
Darlington transistors per TSSOP package. You have to make a 50V
commutator diode tap on your PS, but it works well.

For individual transistors, the SOT-23 MMBTA92 is commonly used, but
placing 30 of those on a board is not my idea of fun, even with pick and
place.

--
David Forbes, Tucson AZ

[Nick]

On Monday, 5 May 2014 18:04:34 UTC+1, nixiebunny wrote:

For individual transistors, the SOT-23 MMBTA92 is commonly used

Do you mean MMBTA42 - the '92 is PNP - most folk I know of use the '42 (NPN)

Nick 

[David Forbes]

Of course. Silly me. The '92 is a PNP anode driver transistor.
If I used them more often, I'd get those numbers straight.

[greg...@hotmail.com]

For NMOS, I prefer Fairchild FQS4901 surface-mount because they are dual 400V units in a reasonable-sized package (small enough to save space, but not so small that they are difficult to hand-solder). Vgs(on) is about 4 volts, so I would NOT use these with logic running at 3.3V or even 3.7V. I actually had the driver for this device running at 12V

For NPN, I use PMBTA42DS device from NXP. They are also dual units and are rated at 300Vceo .

If you are going to drive a dekatron, you do NOT need a high-voltage device as long as all of the cathodes have series resistors. It only takes about 20-30 volts difference between cathodes to "rotate" the dekatron.

[chuck richards]

MPS A42. NPN. Used 15 per board to make driver cards
for each B-7971 tube, in a 16-tube array here.

Each of those driver boards has those 15 transistors being
operated by the outputs of (2) 74LS273 ics. Those ics store
the segment pattern to light the tube segments in any
order, in any pattern.

Then, using the parallel-load data pins on those ics, commoned
up to a 15-bit bus, and then strobing the appropriate tube's
set of 'LS 273s, via the "load" pin, digits or characters can
be put up on the tubes at will.

Soldering down 15 transistors per card, and making 16 cards
was fun, and it was done while watching lots of Howard Stern
on TV, back when he was on *plain old antenna* TV.

The cards are 4 inch square Radio Shack 276-154A, and they have
the handy-dandy 22/44 edge connector.

That so far is my favorite tube-driver project.
I made two little custom card cages holding 8 cards each, to
house these. Then, the entire scrolling circuit and storage
of large blocks of text was done with another several bucket loads
of TTL and an old ASCII keyboard, and a non-volatile SRAM to hold
the data to be scrolled.

Chuck

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[Quixotic Nixotic]

On 5 May 2014, at 18:04, David Forbes wrote:

For individual transistors, the SOT-23 MMBTA92 is commonly used, but placing 30 of those on a board is not my idea of fun, even with pick and place.

Cut the number of tubes down David.

When I dun Nicko's "Nick 'o' Time" (geddit?) clock for our dear leader, I found that MMBTA42s were good for home etch boards, because I didn't have to drill the holes and I could cram the trannies up against the nixie pins. I'd rather solder up the little fleas than drill the holes. So I do MMBTA42s often. MPSA42s are my friends too. 

I don't do multiplex nixie designs. I am considering using 12C port expanders and separate transistors for a forthcoming project.

John S