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I am using a circuit to drive high voltage display tubes (170V DC, 3mA).

Currently, the tubes get switched by an arduino. The output pin is hooked up to a MMBT42 transistor and a 10kOhm base resistor.

I want to use a PCB, with 80 of those lamps. So I need at least 80 transistors and 80 resistors, which is is a lot of work to solder the parts.

Now I wonder, if I could replace the resistor/transistor with this mosfet because the mosfet does not need a resistor.

This BSS131 is a logic-level Mosfet, according to the datasheet.

Would this suit for my application?

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  • \$\begingroup\$ 80! How can you toggle all 80 using only Arduino? I was thinking about IO Expander \$\endgroup\$
    – User323693
    Jul 9, 2015 at 10:04
  • \$\begingroup\$ Im just using the arduino code, on my pcb there will be two ATMEGA2560, so i have 105 outputs :) \$\endgroup\$
    – sgt_johnny
    Jul 9, 2015 at 10:13
  • \$\begingroup\$ Wow, a 2560's an expensive and complex way to get a bunch of digital outputs! \$\endgroup\$
    – Nick Johnson
    Jul 9, 2015 at 10:46
  • \$\begingroup\$ Its not about the outputs. The problem with the normal megas, is the memory, the bootloader takes about 5kb, then on a Atmega328 ist only 27kb left. When using a few libraries and a lot of code, then this can be a serious problem... \$\endgroup\$
    – sgt_johnny
    Jul 9, 2015 at 11:13
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    \$\begingroup\$ Which kind of features will the nixie clock have to fill 27 kB of code? Just curious. Anyway, consider 74HC595 and variants, they are inexpensive and offer a lof of outputs. \$\endgroup\$
    – FarO
    Jul 9, 2015 at 12:33

1 Answer 1

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You haven't said what voltage you're driving the gate from, but this should work fine. If you take a look at figure 5, you can see the maximum current the FET can conduct at different gate drive levels; at 3.3v gate drive it can conduct just under 200mA.

Note, however, that unless you can guarantee that your gate will never be floating, you should include a pulldown resistor to ground on the gate. Otherwise, when the gate is floating - for instance, because the MCU it's connected to isn't initialized yet - it can take on any value, and may turn on or off unexpectedly.

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  • \$\begingroup\$ Thanks for your answer. The drive voltage will be 5V. I only need like 5mA. I know about the floating, but its for a nixie clock, and i can live with it if the digits flicker shortly when power is turned on. And it takes just a few milliseconds to initialize the MCU. I just wanna save pcb-space and not solder 80 resistors per board :) \$\endgroup\$
    – sgt_johnny
    Jul 9, 2015 at 10:00

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